ConspectusAdaptable crystalline frameworks are important in modern solid-state chemistry as they are able to accommodate a wide range of elements, oxidation states, and stoichiometries. Owing to this ability, such adaptable framework structures are emerging as the prototypes for technologically important advanced functional materials. In this Account, the idea of cosubstitution is explored as a useful “pairing” concept that can potentially lead to the creation of many new members of one particular framework structure. Cosubstitution as practiced is the simultaneous replacement of two or more cations, anions, complex anions, other fundamental building units, or vacancies. Although the overall sum of the oxidation states is constant, each component is not necessarily isovalent. This methodology is typically inspired by either mineral-type structural prototypes found in nature or those discovered in the laboratory. Either path leads to the appearance of new phases and the discovery of new materials. In addition, the chemical cosubstitution approach can be successfully adopted to improve physical properties associated with structures.This Account is structured as follows: first, we illustrate the significance and background of chemical cosubstitution by reviewing mineral-inspired structures, such as perovskite and lyonsite, and the structural unit discovered in some selected solid state compounds. With time, the number of lyonsite related phases should rival or even surpass the perovskite family. Several members of the lyonsite-type have been identified as Li-ion conductors and photocatalysts. There is also a noncentrosymmetric structure-type, and therefore the other properties associated with the loss of inversion symmetry should be anticipated. Next, we illustrate recent advances in the synthesis of the new cosubstituted solid state materials from our two groups including (1) nonlinear optical materials, (2) luminescent materials, (3) transparent conducting oxides, and (4) photocatalyst and photovoltaic materials. We emphasize that a concerted and rigorous theoretical and experimental approach will be required to define thermodynamic stability of the complex cosubstitution chemistries, structures, and properties that are yet unknown. We conclude by summarizing the topic and suggesting other possible adaptable framework structures where cosubstitution can be expected.

Chemisorption of pyridine and atmospheric CO2 followed by means of visible Raman and DRIFT spectroscopy were employed to investigate the surface acidity and structure of as-prepared SrTiO3 (STO) samples synthesized using three different approaches, solid-state reaction, molten salt, and sol-precipitation–hydrothermal treatment. Samples prepared via solid-state reaction consisted of irregularly shaped polycrystalline grains with a BET surface area of ∼2 m2/g, whereas those obtained via molten salt synthesis and sol-precipitation–hydrothermal treatment were single-crystalline nanocubes with the {100} faces primarily exposed and BET surface areas of ∼10 and 20 m2/g, respectively. Pyridine and atmospheric CO2 chemisorption demonstrated that the differences in surface acidity between samples synthesized using different approaches are rather slight with a mixture of SrO-based and TiO-based terminations observed in all cases. In contrast, the typology of surface carbonate species arising from the reactive adsorption of atmospheric CO2 varied significantly between samples, indicating the atomic structure of STO surfaces depends strongly on the synthetic method employed. The presence of coordinatively unsaturated Ti4+ acid centers and highly nucleophilic O2− anions is particularly relevant in the perspective of employing morphology-controlled perovskite nanoparticles as supports in catalytic applications such as the oxidation of hydrocarbons.

Nonlinear optical materials are essential for the development of solid-state lasers. KBe2BO3F2 (KBBF) is a unique nonlinear optical material for generation of deep-ultraviolet coherent light; however, its industrial application is limited. Here, we report a new material NH4B4O6F, which exhibits a wide deep-ultraviolet transparent range and suitable birefringence that enables frequency doubling below 200 nm. NH4B4O6F possesses large nonlinear coefficients about 2.5 times that of KBBF. In addition, it is easy to grow bulk crystals and does not contain toxic elements.

Controlled photoluminescence tuning is important for the optimization and modification of phosphor materials. Herein we report an isostructural solid solution of (CaMg)x(NaSc)1–xSi2O6 (0 < x < 1) in which cation nanosegregation leads to the presence of two dilute Eu2+ centers. The distinct nanodomains of isostructural (CaMg)Si2O6 and (NaSc)Si2O6 contain a proportional number of Eu2+ ions with unique, independent spectroscopic signatures. Density functional theory calculations provided a theoretical understanding of the nanosegregation and indicated that the homogeneous solid solution is energetically unstable. It is shown that nanosegregation allows predictive control of color rendering and therefore provides a new method of phosphor development.

Phase transitions are ubiquitous in structurally complex transition metal compounds composed of homoanionic polyhedra, including nitrides, oxides, and fluorides. The symmetry breaking that occurs across polymorphic transitions is often achieved by small atomic displacements, rendering these displacive transitions reversible. In contrast, elemental crystals, alloys, and simple minerals will exhibit reconstructive “bond-breaking” transitions. Here we show that a reconstructive transition occurs in the heteroanionic compound KNaNbOF5, owing to reorientations of the [NbOF5]2– units that trigger a reconfiguration of the cation lattice. Using a combination of synchrotron-based measurements, empirical dynamic simulations, and ab initio calculations, we report structure changes across the transition and formulate an atomistic minimum energy transition path to explain its irreversible nature. Our results indicate that multianionic compounds are likely to host reconstructive transitions that are frequently difficult to study and functionalize in simpler compounds. We anticipate that our insight into the forces that drive the transition will also lead to novel methods to control the assembly of structures in the solid state.

LiCs2PO4, a new deep-ultraviolet (UV) transparent material, was synthesized by the flux method. The material contains unusual edge-sharing LiO4-PO4 tetrahedra. It exhibits a very short absorption edge of λ = 174 nm and generates the largest powder second harmonic generation (SHG) response for deep-UV phosphates that do not contain additional anionic groups, i.e., 2.6 times that of KH2PO4 (KDP). First-principles electronic structure analyses confirm the experimental results and suggest that the strong SHG response may originate from the aligned nonbonding O-2p orbitals. The discovery and characterization of LiCs2PO4 provide a new insight into the structure–property relationships of phosphate-based nonlinear optical materials with large SHG responses and short absorption edges.

A new strontium beryllium borate fluoride, Sr3[(BexB1–x)3B3O10][Be(O1–xFx)3] x = 0.30 (SBBOF), designed to be used in the deep-UV nonlinear optical (NLO) application, was grown by the spontaneous crystallization of a molten flux of SrO–B2O3–LiF. It crystallizes in the space group R3m (No. 160) with the following unit cell dimensions: a = 10.3179(11) Å, c = 8.3958(13) Å, V = 774.1(2) Å3, and Z = 3. SBBOF consists of [(BexB1–x)3B3O10] anionic groups and isolated [Be(O1–xFx)3] planar groups. Importantly, a new strategy to improve the birefringence was introduced by changing the local configuration of isolated structural units from trigonal pyramids to planar triangles. UV–vis diffuse reflectance spectroscopy indicates that the short-wavelength absorption edge of SBBOF is below 200 nm. The band structure and refractive index were calculated. Second harmonic generation (SHG) was measured using the Kurtz and Perry technique, which showed that SBBOF is a phase-matchable material in both visible and UV regions, and its measured SHG coefficient is 2.2 times as large as that of d36 (KDP) at 1064 nm.

Catalyst support materials of tetragonal ZrO2, stabilized by either La2O3 (La2O3–ZrO2) or CeO2 (CeO2–ZrO2), were synthesized under hydrothermal conditions at 200 °C with NH4OH or tetramethylammonium hydroxide as the mineralizer. From in situ synchrotron powder X-ray diffraction and small-angle X-ray scattering measurements, the calcined La2O3–ZrO2 and CeO2–ZrO2 supports were nonporous nanocrystallites that exhibited rectangular shapes with a thermal stability of up to 1000 °C in air. These supports had an average size of ∼10 nm and a surface area of 59–97 m2/g. The catalysts Pt/La2O3–ZrO2 and Pt/CeO2–ZrO2 were prepared by using atomic layer deposition with varying Pt loadings from 6.3 to 12.4 wt %. Monodispersed Pt nanoparticles of ∼3 nm were obtained for these catalysts. The incorporation of La2O3 and CeO2 into the t-ZrO2 structure did not affect the nature of the active sites for the Pt/ZrO2 catalysts for the water–gas shift reaction.

The structure solution of the modulated, delafossite-related, orthorhombic Ga3–xIn3TixO9+x/2 for x = 1.5 is reported here in conjunction with a model describing the modulation as a function of x for the entire system. Previously reported structures in the related A3–xIn3TixO9+x/2 (A = Al, Cr, or Fe) systems use X-ray diffraction to determine that the anion lattice is the source of modulation. Neutron diffraction, with its enhanced sensitivity to light atoms, offers a route to solving the modulation and is used here, in combination with precession electron diffraction tomography (PEDT), to solve the structure of Ga1.5In3Ti1.5O9.75. We construct a model that describes the anion modulation through the formation of rutile chevrons as a function of x. This model accommodates the orthorhombic phase (1.5 ≤ x ≤ 2.1) in the Ga3–xIn3TixO9+x/2 system, which transitions to a biphasic mixture (2.2 ≤ x ≤ 2.3) with a monoclinic, delafossite-related phase (2.4 ≤ x ≤ 2.5). The optical band gaps of this system are determined, and are stable at ∼3.4 eV before a ∼0.4 eV decrease between x = 1.9 and 2.0. After this decrease, stability resumes at ∼3.0 eV. Resistance to oxidation and reduction is also presented.

Mid-IR nonlinear optical (NLO) materials are of great importance in modern laser frequency conversion technology and optical parametric oscillator processes. However, the commercially available IR NLO crystals (e.g., AgGaQ2 (Q = S, Se) and ZnGeP2) suffer from two obstacles, low laser damage thresholds (LDTs) and the difficulty of obtaining high-quality crystals, both of which seriously hinder their applications. The introduction of Cl, an element with a large electronegativity, and Pb, a relatively heavy element to promote the optical properties, affords an oxide-based IR NLO material, Pb17O8Cl18 (POC). High-quality POC single crystals with sizes of up to 7 mm × 2 mm × 2 mm have been grown in an open system. Additionally, POC exhibits a large LDT of 408 MW/cm2, 12.8 times that of AgGaS2. POC also exhibits an excellent second harmonic generation response: 2 times that of AgGaS2, the benchmark IR NLO crystal at 2090 nm, and 4 times that of KDP, the standard UV NLO crystal at 1064 nm. Thus, we believe that POC is a promising IR NLO material.

The union of structural and spectroscopic modeling can accelerate the discovery and improvement of phosphor materials if guided by an appropriate principle. Herein, we describe the concept of “chemical unit cosubstitution” as one such potential design scheme. We corroborate this strategy experimentally and computationally by applying it to the Ca2(Al1–xMgx)(Al1–xSi1+x)O7:Eu2+ solid solution phosphor. The cosubstitution is shown to be restricted to tetrahedral sites, which enables the tuning of luminescent properties. The emission peaks shift from 513 to 538 nm with a decreasing Stokes shift, which has been simulated by a crystal-field model. The correlation between the 5d crystal-field splitting of Eu2+ ions and the local geometry structure of the substituted sites is also revealed. Moreover, an energy decrease of the electron–phonon coupling effect is explained on the basis of the configurational coordinate model.

The perovskite compounds La0.33Sr0.67Cr1–x–yFexRuyO3−δ (LSCrFeRu, x = 0.62, 0.57, and 0.47; y = 0.05, 0.14, and 0.2, respectively) were synthesized and assessed as a new type of solid oxide fuel cell (SOFC) anode in composite with Gd0.1Ce0.9O2-β (GDC) in La0.9Sr0.1Ga0.8Mg0.2O3-ε/La0.4Ce0.6O2 bilayer electrolyte-supported cells. By comparing anode polarization resistance RP,A values for the LSCrFeRu compounds to the either exclusively Fe- or Ru-substituted (La,Sr)CrO3−δ perovskites, the present results demonstrate that the two substituent cations work synergistically to provide further reduction in RP,A from 0.290 Ω·cm2 for La0.33Sr0.67Cr0.33Fe0.67O3−δ (LSCrFe) and 0.235 Ω·cm2 for La0.8Sr0.2Cr0.8Ru0.2O3−δ (LSCrRu) to 0.195 Ω·cm2 for LSCrFeRu (all measured in humidified hydrogen at 800 °C). These impedance results also strongly suggest that hydrogen dissociative adsorption was the rate-limiting step in the hydrogen oxidation reaction sequence for LSCrFe anodes at some of the pH2 and temperatures measured. However, the formation of Ru nanoparticles on LSCrFeRu and LSCrRu surfaces, observed by scanning and transmission electron microscopy, appears to promote hydrogen dissociation. Substituting even small amounts of Ru into (La,Sr)(Cr,Fe)O3−δ perovskites is thus sufficient to make hydrogen electrochemical oxidation the rate-limiting step, resulting in anodes with significantly reduced RP,A.

We report the discovery of Zn0.456In1.084Ge0.460O3, a material closely related to bixbyite. In contrast, however, the oxygen atoms in this new phase occupy 4 Wyckoff positions, which result in 4 four-coordinate, 24 six-coordinate (2 different Wyckoff positions), and 4 eight-coordinate sites as compared to the 32 six-coordinate (also 2 different Wyckoff positions) sites of bixbyite. This highly ordered material is related to fluorite, Ag6GeSO8, and γ-UO3 and is n-type with a bulk carrier concentration of 4.772 × 1014 cm–3. The reduced form displays an average room temperature conductivity of 99(11) S·cm–1 and an average optical band gap of 2.88(1) eV. These properties are comparable to those of In2O3, which is the host material for the current leading transparent conducting oxides. The structure of Zn0.456In1.084Ge0.460O3 is solved from a combined refinement of synchrotron X-ray powder diffraction and time-of-flight neutron powder diffraction and confirmed with electron diffraction. The solution is a new, layered, tetragonal structure in the I41/amd space group with a = 7.033986(19) Å and c = 19.74961(8) Å. The complex cationic topological network adopted by Zn0.456In1.084Ge0.460O3 offers the potential for future studies to further understand carrier generation in ∼3 eV oxide semiconductors.

The 6-coordinated cation site is the fundamental building block of the most effective transparent conducting oxides. Ga2In6Sn2O16, however, maintains 4-, 6-, 7-, and 8-coordinated cation sites and still exhibits desirable transparency and high conductivity. To investigate the potential impact of these alternative sites, we partially replace the Sn in Ga2In6Sn2O16 with Ti, Zr, or Hf and use a combined approach of density functional theory-based calculations, X-ray diffraction, and neutron diffraction to establish that the substitution occurs preferentially on the 7-coordinate site. In contrast to Sn, the empty d orbitals of Ti, Zr, and Hf promote spd covalency with the surrounding oxygen, which decreases the conductivity. Pairing the substitutional site preference with the magnitude of this decrease demonstrates that the 7-coordinate site is the major contributor to conductivity. The optical band gaps, in contrast, are shown to be site-independent and composition-dependent. After all 7-coordinate Sn has been replaced, the continued substitution of Sn results in the formation of a 7-coordinate In antisite or replacement of 6-coordinate Sn, depending on the identity of the d0 substitute.

In oxyfluoride chemistry, the [MOxF6–x]2– anions (M = transition metal) are interesting polar building units that may be used to design polar materials, but their polar vs antipolar orientations in the solid state, which directly depend on the interactions between O2–/F– ligands and the extended structure, remain difficult to control. To improve this control, these interactions were assessed through crystallization of five related [MOxF6–x]2– (M = Ti4+, V5+, Mo6+, W6+) anions with organic molecules. The hybrid organic–inorganic compounds, (4,4′-bpyH2)TiF6 (1), (enH2)MoO2F4 (2), (4-hpyH)2MoO2F4·H2O (3), (4,4′-bpyH2)WO2F4 (4), and (4,4′-bpyH2)VOF5 (5), exhibit isolated [MOxF6–x]2– anions in a hydrogen bond network. The analysis of these crystal structures in combination with DFT calculations elucidate how differences in structure directing properties of these anions arise when π-overlap between O 2p orbitals and M d orbitals is weak and significantly affected by an increase of the energy of the d orbitals from 3d to 5d.

Mn3Ta2O8, a stable targeted material with an unusual and complex cation topology in the complicated Mn–Ta–O phase space, has been grown as a ≈3-cm-long single crystal via the optical floating-zone technique. Single-crystal absorbance studies determine the band gap as 1.89 eV, which agrees with the value obtained from density functional theory electronic-band-structure calculations. The valence band consists of the hybridized Mn d–O p states, whereas the bottom of the conduction band is formed by the Ta d states. Furthermore, out of the three crystallographically distinct Mn atoms that are four-, seven-, or eight-coordinate, only the former two contribute their states near the top of the valence band and hence govern the electronic transitions across the band gap.

The syntheses of two noncentrosymmetric (NCS) vanadium oxide–fluoride compounds that originate from the same synthetic reagent concentrations are presented. Hydrothermal and low-temperature syntheses allow the isolation of metastable products that may form new phases (or decompose) upon heating and allow creation of chemically similar but structurally different materials. NCS materials synthesis has been a long-standing goal in inorganic chemistry: in this article, we compare two chemically similar NCS inorganic materials, NaVOF4(H2O) (I) and NaVO2–xF2+x (II; x = 1/3). These materials originate from the same, identical reagent mixtures but are synthesized at different temperatures: 100 °C and 150 °C, respectively. Compound I crystallizes in Pna21: a = 9.9595(4) Å, b = 9.4423(3) Å, and c = 4.8186(2) Å. Compound II crystallizes in P21: a = 6.3742(3) Å, b = 3.5963(2) Å, c = 14.3641(7) Å, and β = 110.787(3)°. Both materials display second-harmonic-generation activity; however, compound I is type 1 non-phase-matchable, whereas compound II is type 1 phase-matchable.

Birefringent materials are of great importance in optical communication and the laser industry, as they can modulate the polarization of light. Limited by their transparency range, few birefringent materials, except α-BaB2O4 (α-BBO), can be practically used in the deep ultraviolet (UV) region. However, α-BBO suffers from a phase transition and does not have enough transparency in the deep UV region. By introducing the relatively small alkali metal Na+ cation and the F– anion to keep the favorable structural features of α-BBO, we report a new birefringent crystal Na3Ba2(B3O6)2F (NBBF), which has the desirable optical properties. NBBF not only maintains the large birefringence (Δn = no – ne = 0.2554–0.0750 from 175 nm to 3.35 μm) and extends its UV cutoff edge to 175 nm (14 nm shorter than α-BBO) but also eliminates the phase transition and has the lowest growth temperature (820 °C) among birefringent materials. These results demonstrate that NBBF is an attractive candidate for the next generation of deep UV birefringent materials.

Atomic surface structures of CeO2 nanoparticles are under debate owing to the lack of clear experimental determination of the oxygen atom positions. In this study, with oxygen atoms clearly observed using aberration-corrected high-resolution electron microscopy, we determined the atomic structures of the (100), (110), and (111) surfaces of CeO2 nanocubes. The predominantly exposed (100) surface has a mixture of Ce, O, and reduced CeO terminations, underscoring the complex structures of this polar surface that previously was often oversimplified. The (110) surface shows “sawtooth-like” (111) nanofacets and flat CeO2–x terminations with oxygen vacancies. The (111) surface has an O termination. These findings can be extended to the surfaces of differently shaped CeO2 nanoparticles and provide insight about face-selective catalysis.

Nonlinear optical (NLO) crystals are essential materials for generation of coherent UV light in solid state lasers. KBBF is the only material that can achieve coherent light below 200 nm by direct second harmonic generation (SHG). However, its strong layer habits and the high toxicity of the beryllium oxide powders required for synthesis limit its application. By substituting Be with Zn and connecting adjacent [Zn2BO3O2]∞ layers by B3O6 groups, a new UV nonlinear optical material, Cs3Zn6B9O21, was synthesized. It overcomes the processing limitations of KBBF and exhibits the largest SHG response in the KBBF family.

The perovskite series, La1–xSrxCr1–xFexO3-δ (x = 0.2, 0.3, 0.4, 0.5, 0.67, LSCrFe), was synthesized and examined as both single phase and LSCrFe–Gd0.1Ce0.9O2-β (GDC) composite solid oxide fuel cell anodes in full cells with La0.9Sr0.1Ga0.8Mg0.2O3-ε/La0.4Ce0.6O2 bilayer electrolytes. Each anode demonstrated marked improvement in polarization resistance compared to prior studies on Fe-free La1–xSrxCrO3-δ-based anodes and in stability compared to studies on more Fe-rich compositions. Higher Fe content anodes yielded lower polarization resistances, with the x = 0.67 anodes obtaining resistances of 0.275 Ω·cm2 for LSCrFe and 0.333 Ω·cm2 for LSCrFe-GDC in humidified H2 at 800 °C. The lower polarization resistance with increasing Fe content can be attributed to oxygen loss, which introduces significant ionic conductivity into these perovskites. Substitution of an intermediate amount of Fe and Sr into the perovskites can thus optimize anode performance.

In this study, we describe the crystallization of specific niobium oxide–fluoride anions (either [NbOF4]− or [NbOF5]2–) by increasing the fluoride concentration with the appropriate use of organic bases with varied corresponding pKa values to create suitable equilibria for the formation of each anion. HpyNbOF4 (I; py = pyridine) contains the [NbOF4]− anion, while [H2(4,4′-bpy)]NbOF5] (II; 4,4′-bpy = 4,4′-bipyridyl) contains the [NbOF5]2– anion; their identity is correlated with reagent ratios. The increase of basic species (proton acceptors) results in an increase in the fluoride concentration and high fluoride-containing anions. The crystallization of [NbOF4]− in [NbO2/2F4]∞ chains in I was controlled with the use of weak base pyridine (pKa = 5.23), while isolated [NbOF5]2– crystallized in II with strong base 4,4′-bipyridyl (pKa = 10.5). This approach can be broadly applied to target-specific basic building units for fundamentally new and potentially functional solid-state materials.

A series of pseudosymmetrical structures of formula K10(M2OnF11–n)3X (M = V and Nb, n = 2, X = (F2Cl)1/3, Br, Br4/2,I4/2; M = Mo, n = 4, X = Cl, Br4/2, I4/2) illustrates generation of polar structures with the use of Λ-shaped basic building units (BBUs). For a compound to belong to a polar space group, dipole moments of individual species must be partially aligned. Incorporation of d0 early transition metal polyhedral BBUs into structures is a common method to create polar structures, owing to the second-order Jahn–Teller distortion these polyhedra contain. Less attention has been spent examining how to align the polar moments of BBUs. To address alignment, we present a study on previously reported bimetallic BBUs and synthesized compounds K10(M2OnF11–n)3X. These materials differ in their (non)centrosymmetry despite chemical and structural similarities. The vanadium compounds are centrosymmetric (space groups P3̅m1 or C2/m) while the niobium and molybdenum heterotypes are noncentrosymmetric (Pmn21). The difference in symmetry occurs owing to the presence of linear, bimetallic BBUs or Λ-shaped bimetallic BBUs and related packing effects. These Λ-shaped BBUs form as a consequence of the coordination environment around the bridging anion of the metal oxide fluoride BBUs.

The valence matching principle is used to explain the loss of inversion symmetry in the noncentrosymmetric (NCS) polymorph of KNaNbOF5 in comparison to its centrosymmetric (CS) polymorph. The [NbOF5]2– anion has five contacts to both potassium and sodium in the NCS polymorph, whereas in the CS polymorph there are only four contacts to potassium and six contacts to sodium. The lower average Lewis acidity of the cationic framework in the NCS polymorph relative to the CS polymorph reflects the loss of inversion symmetry. This lower average Lewis acidity is achieved during hydrothermal synthesis with a potassium-rich solution when the K:Na ratio in the reaction is greater than 1:1, as the Lewis acidity of potassium is lower than that of sodium. The contrasting coordination environments are manifested in secondary distortions that weaken the primary Nb═O interaction and lengthen the Nb═O bond in the NCS polymorph. An unusual heat-induced phase transition from the CS to the NCS polymorph was studied with in situ powder X-ray diffraction. The transition to the NCS polymorph upon cooling occurs through an intermediate phase(s).

The controlled crystallization of specific tantalum oxide-fluoride and tantalum fluoride anions ([TaOF5]2–, [TaF6]−, and [TaF7]2–) is demonstrated using organic reagents with varied corresponding pKa values in the presence of aqueous hydrofluoric acid. The identity of tantalum oxide-fluoride or fluoride anions of [TaOF5]2–, [TaF6]−, and [TaF7]2– are shown to crystallize successively from solution to solid state by increasing the corresponding pKa of organic reagents, which lead to the subsequent increase of fluoride concentration in the hydrofluoric acid solution. With the use of this methodology, three new hybrid crystal structures were targeted: [H2(2,2′-bpy)]TaOF5 (2,2′-bpy = 2,2′-bipyridyl) 1, [Hdpa]TaF6 (dpa = 2,2′-dipyridylamine) 2, and [H2En]TaF7 (En = ethylenediamine) 3, respectively. The applicability and comparison of this methodology for tantalum and previously prepared niobium compounds show that it can be broadly used to design new materials with specific functionalities for other transition metal oxide-fluorides.

For a crystal to exhibit nonlinear optical (NLO) activity such as second-harmonic generation (SHG), it must belong to a noncentrosymmetric (NCS) space group. Moreover, for these nonlinear optical (NLO) materials to be suitable for practical uses, the synthesized crystals should be phase-matchable (PM). Previous synthetic research into SHG-active crystals has centered on (i) how to create NCS compounds and/or (ii) how to obtain NCS compounds with high SHG efficiencies. With these tactics, one can synthesize a material with a high SHG efficiency, but the material could be unusable if the material was nonphase-matchable (non-PM). To probe the origin of phase matchability of NCS structures, we present two new chemically similar hybrid compounds within one composition space: (I) [Hdpa]2NbOF5·2H2O and (II) HdpaNbOF4 (dpa = 2,2′-dipyridylamine). Both compounds are NCS and chemically similar, but (I) is non-PM while (II) is PM. Our results indicate—consistent with organic crystallography—the arrangement of the organic molecule within hybrid materials dictates whether the material is PM or non-PM.

We present structural and electrochemical analyses of a new double-wolframite compound: AgNa(VO2F2)2 or SSVOF. SSVOF is fully ordered and displays electrochemical characteristics that give insight into electrode design for energy storage beyond lithium-ion chemistries. The compound contains trioxovanadium fluoride octahedra that combine to form one-dimensional chain-like basic building units, characteristic of wolframite (NaWO4). The 1D chains are stacked to create 2D layers; the cations Ag+ and Na+ lie between these layers. The vanadium oxide-fluoride octahedra are ordered by the use of cations (Ag+, Na+) that differ in polarizability. In the case of sodium-ion batteries, thermodynamically, the use of a sodium anode introduces a 300 mV loss in overall cell voltage as compared to a lithium anode; however, this can be counter-balanced by introduction of fluoride into the framework to raise the reduction potentials via an inductive effect. This allows sodium-ion batteries to have comparable voltages to lithium systems. With SSVOF as a baseline compound, we have identified new materials design rules for emerging sodium-ion systems that do not apply to lithium-ion systems. These strategies can be applied broadly to provide materials of interest for fundamental structural chemistry and appreciable voltages for sodium-ion electrochemistry.

A new strategy using cis-edge or -corner sharing metal-centered octahedra is described which enables interesting frustrated spin lattices to be targeted. The examination of “CuV2” triangular motifs in the two new compounds [enH2]Cu(H2O)2[V2O2F8] (1) and [Cu(H2O)(2,2′-bpy)]2[V2O2F8] (2) (where enH2 = ethylenediammonium and 2,2′-bpy =2,2′-bipyridyl) reveals that the [VOF4]2– anions, which exhibit cis structure directing properties, lead to frustrated lattices owing to the competing ferro and antiferromagnetic interactions. There is direct coordination through two cis F– ligands (i.e., the F– ligand trans to O2– and one equatorial F– ligand) in both 1 and 2 owing to the significant π-bonding between the vanadium and the oxide ligand. We emphasize that most of triangular motifs reported in the literature are built of cis-edge or -corner sharing metal-centered octahedra, thus they can be used to target new materials exhibiting interesting magnetism such as spin frustration.

Microemulsion science has provided a wide range of possibilities in materials fabrication. Here, we describe a novel approach to the synthesis of SrTiO3 nanoparticles of different shapes from a microemulsion. We show that the microemulsion structure plays a critical role in the shape of the nanoparticles, with diffusion-limited growth when normal or reverse micelles are present to nanocuboids with a kinetic-Wulff shape in a lamellar microemulsion leading to nanocuboids. As determined by a combination of in situ small-angle X-ray scattering (SAXS) and wide-angle X-ray scattering (WAXS) as a function of temperature and ex situ high-angle annular dark field (HAADF) imaging, the as-prepared SrTiO3 nanocuboids grow between three layers of water (3 × 1.1 nm) and two layers of oil (2 × 2.3 nm) leading to individual crystals which are uniformly 8 nm thick with somewhat greater lengths and widths.Keywords: lamellar microemulsion; perovskite; SrTiO3 nanocuboids; synthesis; X-ray scattering;

t-ZrO2, synthesized under hydrothermal treatment conditions at 150 °C for 20 h using NaOH as the mineralizer, was phase stable up to 600 °C in air. The t-ZrO2 calcined at 600 °C (denoted as Z600) were nonporous spherical nanocrystallites with an average size of ∼12 nm and a surface area of ∼55 m2/g, which exhibited hydrothermal stability in a wide range of pH environments from acidic to basic conditions at 200 °C for 20 h. Monodispersed platinum nanoparticles ∼1.5 ± 0.3 nm were obtained on the Z600 supported Pt/t-ZrO2 catalyst by the Pt atomic layer deposition (ALD) method. Na ions were found to play a crucial role in the formation of the stable t-ZrO2 by incorporating into the internal crystal structure of ZrO2 during the hydrothermal synthesis. The rate of water-gas-shift (WGS) reaction per mole of surface Pt on the Pt/Z600 catalyst was about five times higher compared to the catalysts prepared on commercial nonporous ZrO2. The incorporation of Na into the t-ZrO2 structure had a synergistic effect: stabilizing ZrO2 in the tetragonal phase and promoting the WGS reaction.Keywords: hydrothermal synthesis; Na; Pt/ZrO2; tetragonal ZrO2; water-gas-shift reaction

A new noncentrosymmetric alkaline earth metal halide borate, BaClBF4, has been synthesized with crystal size up to 6 mm × 6 mm × 3 mm via the hydrothermal method at 200 °C. The crystal structure can be described as an alternate stacking of cationic [Ba2Cl2]2+ layers with anionic [BF4]− layers along the b direction, and the [Ba2Cl2]2+ layer is a pseudo-Aurivillius type layer similar to the [Bi2O2]2+ layer. The transmittance range of BaClBF4 is from 0.18 to 8.5 μm, and the laser damage threshold of the crystal is about 6.8 GW cm−2. EDS, TG-DSC and second harmonic generation investigations are reported. The electronic structure is discussed to explain the structure–property relationships.

Polar chains built from acentric building units are of importance to investigate the mechanisms driving the polar alignment in the solid state. Our attempts to engineer polar chains in mixed metal oxide fluorides M′(2,2′-bpy)(H2O)2MOxF6–x compounds [M′/M = Cu/Ti, Cu/V, Cu/Nb, Cu/Mo, Zn/Mo, and Zn/W] were successful using a combination of acentric anions [MOxF6–x]2– and acentric cations [M′(2,2′-bpy)(H2O)2]2+. A new general insight is also revealed: the alignment of polar units can be described with a “lock and key” model. The role of both the key (the acentric unit) and the lock (its environment) on the polarity in infinite chains is discussed.

Single crystals of cuprous oxide (Cu2O) with minimal defects were grown using the optical floating zone technique. Copper vacancies were removed through the promotion of CuO precipitation within the bulk Cu2O crystal following the reaction CuCuCu2O + VCuCu2O + OOCu2O → CuCuCuO + OOCuO. This reaction was promoted through the use of high purity samples and by growing crystals under an oxidizing atmosphere. Although an increase in the oxygen concentration of the atmosphere will initially increase the oxygen to copper ratio, the excess oxygen in the final Cu2O crystal is ultimately decreased through the formation of CuO as the crystal cools. Copper vacancies were reduced further, and the CuO phase was eventually removed from the Cu2O crystal when thin slices of the crystal were annealed.

A methodology for the design of polar, inorganic structures is demonstrated here with the packing of lambda (Λ)-shaped basic building units (BBUs). Noncentrosymmetric (NCS) solids with interesting physical properties can be created with BBUs that lack an inversion center and are likely to pack into a polar configuration; previous methods to construct these solids have used NCS octahedra as BBUs. Using this methodology to synthesize NCS solids, one must increase the coordination of the NCS octahedra with maintenance of the noncentrosymmetry of the bulk. The first step in this progression from an NCS octahedron to an inorganic NCS solid is the formation of a bimetallic BBU. This step is exemplified with the compound CuVOF4(H2O)7: this compound, presented here, crystallizes in an NCS structure with ordered, isolated [Cu(H2O)5]2+ cations and [VOF4(H2O)]2– anions into Λ-shaped, bimetallic BBUs to form CuVOF4(H2O)6·H2O, owing to the Jahn–Teller distortion of Cu2+. Conversely, the centrosymmetric heterotypes with the same formula MVOF4(H2O)7 (MII = Co, Ni, and Zn) exhibit ordered, isolated [VOF4(H2O)]2– and [M(H2O)6]2+ ionic species in a hydrogen bond network. CuVOF4(H2O)7 exhibits a net polar moment while the heterotypes do not; this demonstrates that Λ-shaped BBUs give a greater probability for and, in this case, lead to NCS structures.

The structures of α- and β-Ag3VO4 were studied via single-crystal X-ray diffraction (XRD). The transition from α-phase to β-phase was found to occur at 110 °C. Single-crystal XRD revealed that the integrity of the single crystals was maintained as Ag3VO4 reversibly transitioned between α-Ag3VO4 and β-Ag3VO4. The optical and electrical properties of polycrystalline α-Ag3VO4 were studied by diffuse reflectance spectroscopy and impedance spectroscopy. In order to assess the optical and electrical properties of β-Ag3VO4, in situ measurements were performed above the phase-transition temperature. Thin films of α-Ag3VO4 were prepared by combinatorial sputtering and pulsed laser deposition (PLD). The crystallographic, optical, and electrical conductivity properties of the α-Ag3VO4 thin films were compared with the bulk properties.Keywords: electrical conductivity; single crystal; thin film; α-Ag3VO4; β-Ag3VO4;

The new lamellar phases [Zn(2,2′-bpy)2(H2O)2](ZrF6)·3H2O (I) and [Ni(2,2′-bpy)3](MoO2F4)·5H2O (II) (bpy = bipyridine), which are built from a chiral cation and respectively an inherently nonpolar and a polar anion, provide two contrasting structures with respect to chirality and polarity in the solid state. Each nonpolar layer of I contains enantiomers of both handednesses; conversely, each layer of II contains only a Δ or Λ enantiomer and polar anions oriented along the b or −b axes. A comparison with previously reported structures reveals which combinations and interactions between chiral and polar basic building units can preserve elements of polarity and chirality in the solid state.

A new route is described that enables the design of polar materials using racemic basic building units (BBUs). Λ- and Δ-[Cu(H2O)(bpy)2]2+ complexes in noncentrosymmetric [Cu(H2O)(bpy)2]2[HfF6]2·3H2O and centrosymmetric [Cu(H2O)(bpy)2][BF4]2 reveal that racemic BBUs in the solid state can lead directly to noncentrosymmetry. The structure is polar if only mirror or glide planes relate the left- and right-handed enantiomers, whereas nonpolar, achiral structures result if rotoinversion relates the left- and right-handed enantiomers. This structural analysis also provides an alternative route in the design of polar materials that had always been engineered from polar BBUs.

The generation of polarity in the solid state necessitates ordered, polar basic-building units (BBUs). This paper examines the evolution of ordered BBUs of 1D chains constructed of early transition metals (ETMs) and late transition metals. The cause of polar distortion orientation is illustrated with subtle alterations in the heterotypic structures of one previously reported compound (CuNbOF5(H2O)2(pyz)3) and three new hybrid materials, presented here: CuNbOF5(H2O)4(pyz)2 (1), CuVOF5(H2O)4(pyz)2 (2) and CuVOF5(H2O)2(pyz)3 (3) (pyz=pyrazine). In contrast to the [NbOF5]2− octahedra of CuNbOF5(H2O)2(pyz)3 and compound (1) that have oxide ligands within the 1D BBUs, the [VOF5]2− octahedra of compounds (2) and (3) contain disordered oxide ligands perpendicular to the chains. To create polar 1D BBUs in the solid state, one must have an understanding of how to direct distortions. We demonstrate that the choice of specific polar BBUs within a distinct environment is necessary for orientational order of the ETM anions.Graphical abstractThe orientational order of [VOF5]2− and [NbOF5]2− polar anions in chains and its influence on noncentrosymmetry are discussed on the basis of the three new hybrid compounds composed of linear chains: (CuVOF5(H2O)4(pyz)2, CuNbOF5(H2O)4(pyz)2 and CuVOF5(H2O)2(pyz)3). Orientational order of the distortion of the early transition metal can be achieved by subtle modifications of the anisotropy in the anionic environment and a proper choice of the polar anion.Highlights► Three new hybrid compounds were characterized by single-crystal XRD. ► [VOF5]2− and [NbOF5]2− anions differ in the nucleophilicities of the ligands. ► The order of the anion is controlled by increasing the anisotropy of its environment.

During reinvestigation of the hydrothermal synthesis reported earlier of the compound cesium nickel phosphide, “CsNiP”, we arrived at a new route to the synthesis of the cesium nickel halide compounds CsNiX3 (X=Cl, Br, I). The method has also been shown to extend to cobalt and iron compounds. Single crystals of these compounds were synthesized in phosphoric acid in sealed autoclaves. Their structures were determined by single-crystal X-ray diffraction methods. The compounds crystallize in the hexagonal space group P63/mmc in the BaNiO3 structure type. The synthetic method and the resultant crystallographic details for CsNiCl3 are essentially identical with those reported earlier for the synthesis and structure of “CsNiP”.Graphical abstractThe CsNiX3 (X=Cl, Br, I) structure. Cesium is blue, nickel is in dark green polyhedra, halide is brown.Highlights► A hydrothermal approach to single crystal growth of cesium transition-metal halides. ► Reexamination of “CsNiP” to determine its composition as CsNiCl3. ► X-ray single-crystal structures of CsNiBr3 and CsNiI3.

Solid oxide fuel cells with LaSr2Fe2CrO9-δ–Gd0.1Ce0.9O2-δ composite anodes were tested in H2, H2S-contaminated H2, and CH4 fuels as well as under redox cycling conditions. The La0.9Sr0.1Ga0.8Mg0.2O3-δ electrolyte supported cells had La0.4Ce0.6O2-δ barrier layers to prevent cation diffusion between LaSr2Fe2CrO9-δ and La0.9Sr0.1Ga0.8Mg0.2O3-δ. After an initial break-in where the performance improved slightly, the cells were stable in humidified H2 with a power density > 0.4 W cm− 2 and an anode polarization resistance as low as 0.22 Ω cm2. Anode polarization resistance showed little or no change after 15 redox cycles at 800 °C. Cell performance was stable with 22 ppm H2S, with only a slight performance decrease relative to pure H2, but higher H2S concentrations caused continuous degradation. Also, the performance in humidified CH4 fuel was quite low.Highlights► LaSr2Fe2CrO9-δ– GDC anode performance can be improved with a La0.4Ce0.6O2-δ barrier layer. ► LaSr2Fe2CrO9-δ– Gd0.1Ce0.9O2-δ did not degrade after 15 redox cycles. ► LaSr2Fe2CrO9-δ– Gd0.1Ce0.9O2-δ anode performance was poor on CH4.

Thin films of corundum-type In2 − 2xZnxSnxO3 (cor-ZITO) were grown on lattice-matched substrates using pulsed laser deposition. The (001) of the corundum-type film grew heteroepitaxial to the (001) of a LiNbO3 substrate with large grains along the in-plane and out-of-plane orientation characterized by glancing incidence X-ray diffraction and four-circle Φ-scans. A film with 34% In (metals basis) exhibited a wide optical gap of 3.9 eV and a modest conductivity of 134 S/cm, which suggests cor-ZITO is a potential low-cost transparent conducting oxide.

Introduction of the Cl– anion in the borate systems generates a new perovskite-like phase, K3B6O10Cl, which exhibits a large second harmonic response, about four times that of KH2PO4 (KDP), and is transparent from the deep UV (180 nm) to middle-IR region. K3B6O10Cl crystallizes in the noncentrosymmetric and rhombohedral space group R3m. The structure consists of the A-site hexaborate [B6O10] groups and the BX3 Cl-centered octahedral [ClK6] groups linked together through vertices to form the perovskite framework represented by ABX3.

The corundum-type In2−2xZnxSnxO3 solid solution (cor-ZITO, x ≤ 0.7) was synthesized at 1000 °C under a high pressure of 70 kbar. cor-ZITO is a high-pressure polymorph of the transparent conducting oxide bixbyite-In2−2xZnxSnxO3 (x ≤ 0.4). Analysis of the extended X-ray absorption fine structure suggests that significant face-sharing of Zn and Sn octahedra occurs, as expected for the corundum structure type. In contrast to the ideal corundum structure, however, Zn and Sn are displaced and form oxygen bonds with lengths that are similar to those observed in high-pressure ZnSnO3. Powder X-ray diffraction patterns of cor-ZITO showed the expected unit cell contraction with increased cosubstitution, but no evidence for ilmenite-type ordering of the substituted Zn and Sn. A qualitative second harmonic generation measurement, for the solid solution x = 0.6 and using 1064 nm radiation, showed that Zn and Sn adopt a polar LiNbO3-type arrangement.

This work highlights a room-temperature composition study of the Ag2O/V2O5/HF(aq) ternary system, leading to the precipitation of either various silver vanadates having Ag/V ratios from 1/2 to 3/1 or the new silver vanadium oxyfluoride compounds Ag4V2O6F2 and Ag3VO2F4, and a synthetic procedure that affords nanocrystalline Ag2V4O11 (SVO) at room temperature. The as-precipitated SVO particles exhibit an acicular morphology, 10−15 × 50−200 nm in size, and present a peculiar reactivity vs lithium notably through a Ag+/Li+ displacement reaction that progresses in a reversible fashion. This step forward thus enables the reversible and simultaneous combination of two active redox processes (silver and vanadium), providing a significant enhancement in the cathode gravimetric capacity of 320 mAh/g at C rate and more than 250 mAh/g at 5C.

Although some perovskite oxides have been shown to be stable solid oxide fuel cell (SOFC) anodes, the actual crystal structure of these materials under operating conditions is largely unknown. In this paper, the structural evolution of the SOFC anode La0.30Sr0.70Fe0.70Cr0.30O3−δ was studied at 800 and 900 °C (similar to SOFC operating temperatures) in progressively reducing and oxidizing environments. The perovskite was shown to be stable down to a pO2 of 10−20 atm at 800 °C and a pO2 of 10−18 atm at 900 °C, at which point a spinel phase formed. Further reduction led to the formation of Fe metal. The phase separation of La0.30Sr0.70Fe0.70Cr0.30O3−δ was also shown to be completely reversible with an increase in the partial oxygen pressure and reoxidation of the sample.

Zinc-indium-tin oxide (ZITO) is a potential replacement for the currently used tin-doped indium oxide (ITO) as a transparent conducting oxide (TCO) for optoelectronic devices. At the present time ITO is the material of choice for the TCO layer, but the increasing cost of indium metal and the advent of new technologies will require alternative TCOs. Over the past 15 years, bulk and thin film studies have been amassed that report the electrical and optical properties of various ZITO compositions. This review will examine the reported data and demonstrate that the bulk subsolidus phase diagram can act as a guide to understanding the numerous and varied results reported for thin films.

We investigated the effect of inserting lithium into Ag2V4O11 (ɛ-SVO) on the structure, electronic properties and redox committed by combining in situ XRD measurements, ESR spectroscopy and 4 probes DC conductivity coupled with thermopower measurements. The electrochemical discharge occurs in three consecutive steps above 2 V (vs. Li+/Li). The first one, between 0 < x < ∼0.7 in Lix-SVO, has been ascribed to the V5+ reduction through a solid solution mechanism. This reduction competes with a Li+/Ag+ displacement reaction which leads to a structural collapse owing to the ionic radii mismatch between the withdrawn Ag+ and the inserted Li+. The silver reduction progresses continuously with two different slopes along two composition–potential plateaus at 2.81 V and 2.55 V. Finally, the reduction continues until we obtain an amorphous structure with V4+ and a ɛ of V3+. Although, the silver re-enters the structure during the subsequent recharge, the original structure is not recovered. The reduction of silver forming silver metal nano-clusters acts to increase the electronic conductivity from 3.8 × 10−5 S cm−1 to 1.4 × 10−3 S cm−1. In complement to this study, we also report on a low temperature hydro-(solvo)-thermal approach using HF(aq) as a mineralizer, which enables the synthesis of nano-sized ɛ-SVO particles that exhibit superior electrochemical performances compared to conventional particles synthesized by solid-state reaction.

As a potential cathode material for the ICD lithium battery, one advantage of Ag6Mo2O7F3Cl (SMOFC) is its enhanced gravimetric capacity of ca. 133 mAh/g above 3 V (vs Li+/Li) delivered by two biphasic transitions at 3.46 and 3.39 V (vs Li+/Li). The unique crystal structure of SMOFC enables a high silver ion conduction: σ⊥[001] = 3.10−2 S/cm (±2.10−2 S/cm) and σ//[001] = 4.10−3 S/cm (±2.10−3 S/cm) and, hence, an excellent discharge rate capability. Lithium insertion has been monitored by in situ XRD measurements with HRTEM investigations. There is a linear isotropic collapse of the structure leading to a fully amorphous structure beyond four inserted lithiums.

Understanding the complex relationship between synthesis conditions, in particular temperature and composition, led to single crystals of the cryolite type phases Ag3MoO3F3 and Ag3VO2F4. These crystals form in a reversible thermodynamic process from dissolved species when the solution is heated. Single crystal structural data reveal the Mo6+ cation distorted toward facially coordinated oxides for Ag3MoO3F3, and the V5+ cation toward the edge of the cis-oxide positions for Ag3VO2F4. Local ordering of oxide and fluoride ligands is observed for both structures.

The local structure of In2O3 cosubstituted with Zn and Sn (In2−2xSnxZnxO3, x≤0.4 or ZITO) was determined by extended X-ray absorption fine structure (EXAFS) for x=0.1, 0.2, 0.3 and 0.4. The host bixbyite In2O3 structure is maintained up to the enhanced substitution limit (x=0.4). The EXAFS spectra are consistent with random substitution of In by the smaller Zn and Sn cations, a result that is consistent with the “good-to-excellent” conductivities reported for ZITO.The local structure of Zn and Sn cosubstituted In2O3 was determined by X-ray absorption spectroscopy, which was consistent with random substitutions of In by Zn and Sn into bixbyite In2O3.

We report the synthesis and structure determination of single crystals of La4Cu3MoO12 grown from a CuO/KCl flux. This material, whose structure had previously been reported based solely on polycrystalline diffraction data, shows frustrated magnetic behavior and an anti-ferromagnetic ordering of spin-1/2 triangles at low temperatures. The structural and atomic parameters determined from the single crystal data are in very good agreement with those reported previously. However, HREM data showed evidence for disorder in the stacking of the Cu3MoO4 planes, and thus a twinned structural refinement in space group P21/m was replaced by an equivalent disordered structural model in space group Pm. This development of a synthetic route to single crystals of La4Cu3MoO12 will allow a more detailed investigation of its complex electronic and magnetic properties.Structural view of a single layer of the triangular lattice of La4Cu3MoO12 perpendicular to the b-axis. The copper atoms are blue, the oxide ions are red and the MoO5 trigonal bipyramids are yellow. The isolated triangular clusters of Cu3O are outlined by the thin blue lines.

New cathode materials will lead to technological advances for implantable cardioverter defibrillators, ICDs, such as reduced size and increased performance of the device. While the industry standard silver vanadium oxide Ag2V4O11 exhibits great chemical/electrochemical stability, dense silver oxide fluoride materials are advantageous because of high crystal density that can result in an increased capacity above 3 V. This report highlights the reactivity at room temperature between Ag2O and V2O5 in an aqueous HF solution which affords a rapid precipitation of sub-micrometer sized Ag4V2O6F2 (SVOF), a high capacity Li-battery cathode material. This system opens new and novel synthetic strategies in the design of new oxide fluoride materials.

The reactivity of Mn2O3 and late rare-earth sesquioxides in alkaline aqueous solution affords a high-yield formation of rare-earth manganites, LnMnO3 (Ln = Ho–Lu and Y). The yield of the products depends significantly on the pH, which determines the solubility of the manganese cation, and reaction temperature, which regulates the decomposition of the insoluble rare-earth trihydroxide, Ln(OH)3, to the more reactive oxide hydroxide, LnO(OH). Plate- and needle-like LnMnO3 crystallites of a few micrometers in size have been prepared at reaction temperatures where the rare-earth oxide hydroxide is thermodynamically stable, whereas at lower temperatures the insoluble rare-earth trihydroxide persists and no reaction is observed.

ForewordPublic awareness of solid-state chemistry, or more broadly solid-state science and technology rapidly grew along with the transistor revolution and the development of the integrated circuit. We are now at the half-way point in the solid state century [Scientific American The Solid-State Century 1997;8(1) [special issue]], a period of the last 50 years when the term “solid state electronics” was in general vernacular and “solid state” was prominently stamped on consumer electronics appliances, almost as a synonym for “advanced” or “modern.”Clearly without the Bell Labs discovery of the first transistor, which boosted an electrical signal a 100-fold, our personal computers would not be possible, and the information age it spawned would never have happened. It is clear with hindsight that those individuals, companies, regions and nations that have embraced the new information technology have flourished.At the present time the solid-state age does not show any sign of stopping. In this the second half of the century, we have chips with 10 million transistors, solar photovoltaics and all—solid-state lighting, cell phones, displays, data storage, the insulated gate bipolar transistor (IGBT) revolutionizing power electronics, and enthusiasm is high for quantum-optical devices which may begin to dominate new technology.The goal of the Solid State Chemistry Workshop was to assess the current state of solid-state chemistry and explore its impact on allied disciplines as well as industry. In this report we articulate the solid-state chemistry community's sense of the future opportunities and directions and make several recommendations. The findings of this workshop could act as a vehicle for informing the solid-state chemistry community of programs and opportunities for support at NSF and elsewhere.This report aims to identify research directions in solid-state chemistry closely aligned with emerging or potential technologies, as well as areas of original research that could lead to new advances in materials science, solid-state physics and the solid-state sciences in general. Of course, judgment must be exercised to distinguish which of such efforts have true fundamental value, and sufficient patience must be accorded for fundamental research to ultimately bring about new technologies.A major societal impact of the solid state and materials chemistry community is the education of students who are able to excel in multidisciplinary areas crucial to the competitiveness of American industry. Solid state and materials chemistry by its nature, with its interdisciplinary history, has the ability to prepare and educate its graduates to excel in a wide variety of industries including the fields of energy, pharmaceuticals, optical materials and all manner of electronic devices, and nano and biotechnology. Since by their nature emerging technologies depend on the discovery of new materials and their properties, individuals with training in solid-state chemistry are key members of research teams and companies developing these technologies.Which scientific disciplines are affected most by what goes on in solid-state chemistry? The focus of the proposed workshop was two-fold, we sought a close look at the discipline of solid-state chemistry in the beginning of the third millennium and explored its continued impact and relationship with allied disciplines in the physical sciences and also industry. This report highlights a number of accomplishments, emerging research directions and areas requiring increased effort but is not meant to be all inclusive and it is certain that we have left out a number of important aspects. An assessment of how solid-state chemistry is impacting the physical sciences, through continuing advances and the many ways of interacting across disciplinary boundaries, could help the National Science Foundation and the scientific community better appreciate its value and contributions in the greater scientific and societal context.The report also includes discussions of existing and new modes for educating students, and the development and use of national facilities for performing state-of-the-art research in our field. A critical enabler of this societal benefit has been funding from the NSF and other agencies in this area, in particular our nation's premier national user facilities.Recommendations1. There is great interest in developing methodologies for synthesis of materials with intended functionalities. To continue the pace of progress solid-state chemistry has enjoyed in the past we recommend sustained support for exploratory synthesis and directed synthesis aimed at new materials' discoveries and the development of methodological and design principles. Syntheses assisted by theory and modeling are only still emerging and should be encouraged.2. Structure–property relationships are the fundamental underpinning of solid-state sciences. Be they experimental or theoretical, efforts and ideas that will make advances in this area should be supported with sustained funding from the Foundation.3. The Foundation should encourage and support outreach ideas aimed at explaining, promoting and projecting the place and significance of solid-state chemistry to society. This could be done under the umbrella of Centers or smaller special projects.4. Fundamental research and materials discovery emanating from NSF and other agency support of solid-state chemistry in academia ultimately affects the strength of industry and therefore the economy. Where appropriate, the NSF should seek the advice of industrial experts in solid-state chemistry as a development tool in formulating potential research directions. In addition existing programs aimed at supporting academic–industry collaborations leveraging industry resources and providing graduate students with goal-driven perspectives are viewed favorably.5. Solid state and materials chemistry research will extract maximum benefit from NSF funding of personnel and support activities in national facilities. These often unique facilities enable the solution of important problems in solid-state chemistry. Greater utilization of these facilities is limited by lack of expertise on the use of these techniques amongst solid-state chemists and limited user support from the facilities. The NSF has an important role to play as an advocate for the needs of solid-state chemistry to the facilities.6. The NSF should consider and implement mechanisms for supporting collaborative research between the solid-state sciences and investigators in far-ranging fields, which may require creative funding mechanisms involving other agencies.7. Programs within NSF that foster collaborative research with international PIs, groups or Institutes such as the Materials World Network should be supported. Also recommended is funding for short term overseas career development ‘sabbaticals’ for faculty and increases in the number of US postdoctoral fellowships for positions abroad with a well-defined NSF affiliation.

A single-step, low-temperature (<210 °C) and -pressure (<20 atm) hydrothermal method has been developed to synthesize a series of silver delafossites, AgBO2 (B = Al, Ga, Sc, and In). Experimental and computational studies were performed to understand the optical and electric properties of these silver delafossites, including the first in-depth study of AgAlO2 and AgScO2. Their properties were examined as a function of the trivalent cation radius and compared to those of copper delafossites to elucidate the role of both the A- and B-site cations. While optical band gaps for silver delafossites were larger and visible light absorption was lower than values previously reported for polycrystalline powder samples of copper delafossites, the conductivities of silver delafossites are similar or lower. Electronic structure calculations indicate that these properties are due to the scarcity of silver 4d states just below the valence band maximum.

Phase-pure BiCuOSe, which is isostructural to the layered p-type transparent conductor LaCuOS, has been synthesized in high yield by a single-step hydrothermal reaction at low temperature (250 °C) and pressure (<20 atm). A moderate reaction temperature of 250 °C was sufficiently high to solubilize both Bi2O3 and Cu2O and stabilize monovalent copper and low enough to impede the oxidation of dianionic selenium. BiCuOSe exhibits a relatively high electrical conductivity (σ ≈ 3.3 S cm−1) and a reduced band gap (Eg = 0.75 eV), which compare favorably with the optoelectronic properties of BiCuOS and the cerium-based oxysulfides, CeAgOS and CeCuOS.

A one-step, corrosion-assisted reaction was developed to synthesize copper sulfide (CuS) from elemental copper and sulfur in water at 60 °C. The as-prepared polycrystalline CuS consists of polyhedral-shaped 2–3 μm crystallites. CuS forms by the oxidation of copper metal in the presence of sulfur, whereas in the presence of water, a continuous solid-state reaction occurs without passivation by the product.

The rational design of crystal structures based on the chemical nature of molecular components, a longstanding and exciting research topic in organic solid state chemistry, is an emerging theme of crystal engineering in inorganic solid state chemistry. In particular, noncentrosymmetric structures, or those lacking inversion symmetry, are important for future technologies that are based on piezoelectricity, pyroelectricity, ferroelectricity and second harmonic generation (SHG). Materials that exhibit these properties provide a large and new class of solids for studies in basic science associated with the noncentrosymmetric (chiral, polar, or chiral–polar) space groups. Structures comprised of vertex-linked octahedra are common in inorganic solids. The subject of our Highlight is the rational synthesis of linear, zigzag or helical chains when two vertices of an octahedron, which are either adjacent (cis) or opposite (trans), are linked.

Disorder between the vanadium and molybdenum sites was investigated using neutron diffraction on polycrystalline samples of M2.5VMoO8 (M=Mg2+, Mn2+, Zn2+) and the distribution of V5+ and Mo6+ among the tetrahedral sites was determined to be nearly statistical. The refined structures for all three polycrystalline samples corroborate those of corresponding single crystals determined previously with X-ray single crystal diffraction. Studies directed at the formation of Mg2.5+xV1+2xMo1−2xO8 (x=0, ±0.02 and ±0.04) demonstrate that the phase begins to form at an appreciable rate at 1173 K, which is approximately 250 K below its melting point.

(Ag3MoO3F3)(Ag3MoO4)Cl was synthesized by hydro(solvato)thermal methods and characterized by single-crystal X-ray diffraction (P3m1, No. 156, Z=1, a=7.4488(6)Å, c=5.9190(7) Å). The transparent colorless crystals are comprised of chains of distorted fac-MoO3F33− octahedra and MoO42− tetrahedra anions, as suggested by the formulas Ag3MoO3F3 and Ag3MoO4+, and are connected through Ag+ cations in a polar alignment along the c-axis. One Cl− anion per formula unit serves as a charge balance and connects the two types of chains in a staggered fashion, offset by . In MoO42−, the Mo atom displaces towards a single oxide vertex, and in MoO3F33−, the Mo displaces towards the three oxide ligands. The ordered oxide–fluoride ligands on the MoO3F33− anion is important to prevent local inversion centers, while the polar organization is directed by the Cl− anion and interchain dipole–dipole interactions. The dipole moments of MoO3F33− and MoO42− align in the negative c-axis direction, to give a polar structure with no cancellation of the individual moments. The direction and magnitude of the dipole moments for MoO3F33− and MoO42− were calculated from bond valence analyses and are 6.1 and 1.9 debye (10−18 esu cm) respectively, compared to 4.4 debye for polar NbO6 octahedra in LiNbO3, and 4.5 debye for polar TiO6 octahedra in KTiOPO4 (KTP).

Potential applications as transparent conducting oxides have made the study of ternary metal oxides based on the delafossite structure very attractive. The well known and understood thermal instability of noble metal oxides, and therefore the associated problems with high-temperature solid-state techniques to yield pure complex oxides based on noble metals, clearly illustrates the need for low-temperature alternatives. For the first time, synthesis of 3R-AgInO2 at low temperature (175 °C) and pressure (<10 atm) was achieved by a single-step hydrothermal technique. Particle size of the orange crystallites ranged from 3 to 7 μm.

The A2CuTiO6 (A=Y, Tb–Lu) series has been reinvestigated in light of the recent discovery of cation order in structurally similar La4Cu3MoO12 and La3Cu2VO9. The crystal structure has been determined by electron and powder X-ray diffraction. The phases crystallize in an hexagonal symmetry, space group P63cm with cell parameters a≈6.2 Å; c≈11.5 Å. In this series of compounds, the Cu(II) and Ti(IV) cations randomly occupy trigonal bipyramids which form layers separated by sevenfold coordinated A(III) cations. This series is isotypical with LuMnO3.Graphic

Subsolidus phase relationships in the Ga2O3SnO2ZnO system were determined at 1250 °C using solid state synthesis and X-ray powder diffraction. The two spinels, Zn2SnO4 and ZnGa2O4, formed a complete solid solution. The optical band gap of the spinel varied with composition from 3.6 eV (Zn2SnO4) to 4.7 eV (ZnGa2O4). All samples were white and insulating except those containing Ga-doped ZnO. The phase relations and physical properties of Ga2O3SnO2ZnO were compared with those of In2O3SnO2ZnO.Graphic

ForewordPublic awareness of solid-state chemistry, or more broadly solid-state science and technology rapidly grew along with the transistor revolution and the development of the integrated circuit. We are now at the half-way point in the solid state century [Scientific American The Solid-State Century 1997;8(1) [special issue]], a period of the last 50 years when the term “solid state electronics” was in general vernacular and “solid state” was prominently stamped on consumer electronics appliances, almost as a synonym for “advanced” or “modern.”Clearly without the Bell Labs discovery of the first transistor, which boosted an electrical signal a 100-fold, our personal computers would not be possible, and the information age it spawned would never have happened. It is clear with hindsight that those individuals, companies, regions and nations that have embraced the new information technology have flourished.At the present time the solid-state age does not show any sign of stopping. In this the second half of the century, we have chips with 10 million transistors, solar photovoltaics and all—solid-state lighting, cell phones, displays, data storage, the insulated gate bipolar transistor (IGBT) revolutionizing power electronics, and enthusiasm is high for quantum-optical devices which may begin to dominate new technology.The goal of the Solid State Chemistry Workshop was to assess the current state of solid-state chemistry and explore its impact on allied disciplines as well as industry. In this report we articulate the solid-state chemistry community's sense of the future opportunities and directions and make several recommendations. The findings of this workshop could act as a vehicle for informing the solid-state chemistry community of programs and opportunities for support at NSF and elsewhere.This report aims to identify research directions in solid-state chemistry closely aligned with emerging or potential technologies, as well as areas of original research that could lead to new advances in materials science, solid-state physics and the solid-state sciences in general. Of course, judgment must be exercised to distinguish which of such efforts have true fundamental value, and sufficient patience must be accorded for fundamental research to ultimately bring about new technologies.A major societal impact of the solid state and materials chemistry community is the education of students who are able to excel in multidisciplinary areas crucial to the competitiveness of American industry. Solid state and materials chemistry by its nature, with its interdisciplinary history, has the ability to prepare and educate its graduates to excel in a wide variety of industries including the fields of energy, pharmaceuticals, optical materials and all manner of electronic devices, and nano and biotechnology. Since by their nature emerging technologies depend on the discovery of new materials and their properties, individuals with training in solid-state chemistry are key members of research teams and companies developing these technologies.Which scientific disciplines are affected most by what goes on in solid-state chemistry? The focus of the proposed workshop was two-fold, we sought a close look at the discipline of solid-state chemistry in the beginning of the third millennium and explored its continued impact and relationship with allied disciplines in the physical sciences and also industry. This report highlights a number of accomplishments, emerging research directions and areas requiring increased effort but is not meant to be all inclusive and it is certain that we have left out a number of important aspects. An assessment of how solid-state chemistry is impacting the physical sciences, through continuing advances and the many ways of interacting across disciplinary boundaries, could help the National Science Foundation and the scientific community better appreciate its value and contributions in the greater scientific and societal context.The report also includes discussions of existing and new modes for educating students, and the development and use of national facilities for performing state-of-the-art research in our field. A critical enabler of this societal benefit has been funding from the NSF and other agencies in this area, in particular our nation's premier national user facilities.Recommendations1. There is great interest in developing methodologies for synthesis of materials with intended functionalities. To continue the pace of progress solid-state chemistry has enjoyed in the past we recommend sustained support for exploratory synthesis and directed synthesis aimed at new materials' discoveries and the development of methodological and design principles. Syntheses assisted by theory and modeling are only still emerging and should be encouraged.2. Structure–property relationships are the fundamental underpinning of solid-state sciences. Be they experimental or theoretical, efforts and ideas that will make advances in this area should be supported with sustained funding from the Foundation.3. The Foundation should encourage and support outreach ideas aimed at explaining, promoting and projecting the place and significance of solid-state chemistry to society. This could be done under the umbrella of Centers or smaller special projects.4. Fundamental research and materials discovery emanating from NSF and other agency support of solid-state chemistry in academia ultimately affects the strength of industry and therefore the economy. Where appropriate, the NSF should seek the advice of industrial experts in solid-state chemistry as a development tool in formulating potential research directions. In addition existing programs aimed at supporting academic–industry collaborations leveraging industry resources and providing graduate students with goal-driven perspectives are viewed favorably.5. Solid state and materials chemistry research will extract maximum benefit from NSF funding of personnel and support activities in national facilities. These often unique facilities enable the solution of important problems in solid-state chemistry. Greater utilization of these facilities is limited by lack of expertise on the use of these techniques amongst solid-state chemists and limited user support from the facilities. The NSF has an important role to play as an advocate for the needs of solid-state chemistry to the facilities.6. The NSF should consider and implement mechanisms for supporting collaborative research between the solid-state sciences and investigators in far-ranging fields, which may require creative funding mechanisms involving other agencies.7. Programs within NSF that foster collaborative research with international PIs, groups or Institutes such as the Materials World Network should be supported. Also recommended is funding for short term overseas career development ‘sabbaticals’ for faculty and increases in the number of US postdoctoral fellowships for positions abroad with a well-defined NSF affiliation.

Oleic acid, an 18-carbon chain fatty acid, has been widely used as a surfactant to fabricate colloidal nanocrystals. In previous work, we discovered a lamellar microemulsion strategy to fabricate sub-20 nm SrTiO3 nanocuboids using oleic acid and oleate species. Here, we demonstrate (i) the general synthesis with lamellar microemulsions of a family of compositionally varied BaxSr1–xTiO3 crystalline nanocuboids with uniform size, and (ii) subsequent assembly into two-dimensional arrays by nanoparticle-bound oleate in a nonpolar solvent. The measured interparticle distance (2.4 nm) of adjacent nanoparticles in an array is less than the length of a double oleate layer (∼4 nm). On the basis of calculations of the interfacial free energy, we propose the hydrophobic, hydrocarbon-terminated groups of oleate from adjacent nanocuboids are situated closely but do not overlap. Lower aspect ratio nanocuboids are bordered by four adjacent nanocuboids which results in a uniform direction self-assembly array, whereas higher aspect ratio nanocuboids are bordered by five or six adjacent nanocuboids and can develop an arced local coordination.

The electrochemical reactivity of the cathode material Ag4V2O6F2 (SVOF) versus lithium, with a particular emphasis on the lithium insertion mechanism, was studied by means of the complementary techniques in situ X-ray diffraction, electron paramagnetic resonance, and high-resolution transmisssion electron microscopy. This study confirms the initial reports of a high capacity for SVOF of 148 mAh/g above 3 V and that the reduction of silver above 3 V (vs Li+/Li0) leads to a loss of SVOF crystallinity until it becomes completely amorphous between the third and fourth lithiums inserted. Next, vanadium is reduced between 2.5 and 1.5 V (vs Li+/Li0) for the fifth and sixth lithiums inserted. In addition, the polarization within the cathode is significantly lower for the vanadium reduction than for the silver reduction. The silver metal morphologies consisted of nanoparticles (∼5 nm diameter) and dendrites and were both seen in samples of lithiated SVOF.

A new noncentrosymmetric alkaline earth metal halide borate, BaClBF4, has been synthesized with crystal size up to 6 mm × 6 mm × 3 mm via the hydrothermal method at 200 °C. The crystal structure can be described as an alternate stacking of cationic [Ba2Cl2]2+ layers with anionic [BF4]− layers along the b direction, and the [Ba2Cl2]2+ layer is a pseudo-Aurivillius type layer similar to the [Bi2O2]2+ layer. The transmittance range of BaClBF4 is from 0.18 to 8.5 μm, and the laser damage threshold of the crystal is about 6.8 GW cm−2. EDS, TG-DSC and second harmonic generation investigations are reported. The electronic structure is discussed to explain the structure–property relationships.

The reactivity of Mn2O3 and late rare-earth sesquioxides in alkaline aqueous solution affords a high-yield formation of rare-earth manganites, LnMnO3 (Ln = Ho–Lu and Y). The yield of the products depends significantly on the pH, which determines the solubility of the manganese cation, and reaction temperature, which regulates the decomposition of the insoluble rare-earth trihydroxide, Ln(OH)3, to the more reactive oxide hydroxide, LnO(OH). Plate- and needle-like LnMnO3 crystallites of a few micrometers in size have been prepared at reaction temperatures where the rare-earth oxide hydroxide is thermodynamically stable, whereas at lower temperatures the insoluble rare-earth trihydroxide persists and no reaction is observed.