Scandium fluoride (ScF3) exhibits a pronounced negative thermal expansion (NTE), which can be suppressed and ultimately transformed into an isotropic zero thermal expansion (ZTE) by partially substituting Sc with Fe in (Sc0.8Fe0.2)F3 (Fe20). The latter displays a rather small coefficient of thermal expansion of −0.17 × 10–6/K from 300 to 700 K. Synchrotron X-ray and neutron pair distribution functions confirm that the Sc/Fe–F bond has positive thermal expansion (PTE). Local vibrational dynamics based on extended X-ray absorption fine structure indicates a decreased anisotropy of relative vibration in the Sc/Fe–F bond. Combined analysis proposes a delicate balance between the counteracting effects of the chemical bond PTE and NTE from transverse vibration. The present study extends the scope of isotropic ZTE compounds and, more significantly, provides a complete local vibrational dynamics to shed light on the ZTE mechanism in chemically tailored NTE compounds.

The unique physical property of negative thermal expansion (NTE) is not only interesting for scientific research but also important for practical applications. Chemical modification generally tends to weaken NTE. It remains a challenge to obtain enhanced NTE from currently available materials. Herein, we successfully achieve enhanced NTE in Pb(Ti1–xVx)O3 by improving its ferroelectricity. With the chemical substitution of vanadium, lattice tetragonality (c/a) is highly promoted, which is attributed to strong spontaneous polarization, evidenced by the enhanced covalent interaction in the V/Ti–O and Pb–O2 bonds from first-principles calculations. As a consequence, Pb(Ti0.9V0.1)O3 exhibits a nonlinear and much stronger NTE over a wide temperature range with a volumetric coefficient of thermal expansion αV = −3.76 × 10–5/°C (25–550 °C). Interestingly, an intrinsic giant volume contraction (∼3.7%) was obtained at the composition of Pb(Ti0.7V0.3)O3 during the ferroelectric-to-paraelectric phase transition, which represents the highest value ever reported. Such volume contraction is well correlated to the effect of spontaneous volume ferroelectrostriction. The present study extends the scope of the NTE family and provides an effective approach to explore new materials with large NTE, such as through adjusting the NTE-related ferroelectric property in the family of ferroelectrics.

Semiconductor functional materials have been widely applied in electronic devices. However, the reliability and lifetime of the devices suffer from the undesirable mismatch of the coefficients of thermal expansion. It is important to develop semiconductor materials with controllable thermal expansion. Here, we develop a remarkable group of ferroelectric semiconductor materials (1 − x)PbTiO3–xBi(Co2/3Nb1/3)O3 (PT–100xBCN) that have not only tunable electronic and optical properties, but also controllable negative, zero, and positive thermal expansion. Through the BCN chemical substitution, the bandgap (Eg) is reduced from 2.60 eV to 2.26 eV to achieve semiconducting properties in PbTiO3-based ferroelectrics. Meanwhile, we have achieved a gradual transition from negative, to zero, and then to positive thermal expansion (αV: −12.3 × 10−6 to 7.4 × 10−6 K−1). Besides, PT–BCN exhibits ferroelectric and piezoelectric properties. The relatively high piezoelectric coefficient d33 ∼ 200 pC N−1 was achieved in the composition of PT–42BCN near the morphotropic phase boundary. PT–BCN shows good negative temperature coefficient (NTC) thermistor characteristics. The coexistence of light absorption, thermal expansion, and electronic properties in PT–BCN makes it a promising material for future applications. The present study would offer an approach to developing and exploring new multifunctional semiconducting materials with controllable thermal expansion.

To meet the increasing demand for high temperature piezoelectric actuator and transducer applications, much attention has been paid on exploring piezoelectric materials which can work efficiently under high temperature conditions. In the present study, a new Bi-based perovskite (ABO3) of (1 − x)PbTiO3-xBi(Zn1/2Hf1/2)O3 has been investigated. For the compositions of x < 0.20, it is interesting to observe that the tetragonality (c/a) remains relatively constant over the entire tetragonal phase. This unusual phenomenon is in contrast to the behavior of most PbTiO3-based solid solutions, wherein the c/a is usually reduced. As a result, the Curie temperature (TC) increases from 490 °C for pure PbTiO3, to as high as 528 °C for x = 0.10, indicating the present PbTiO3-Bi(Zn1/2Hf1/2)O3 to be a high-TC piezoelectric material. It is proposed that the maintained large tetragonality and high TC could be attributed to the large spontaneous polarization (PS) displacements induced by the strong Pb/Bi-O hybridization and coupling interactions between Pb/Bi and B-site ferroelectric-active cations.

It is an interesting but challenge issue to prepare isotropic controllable thermal expansion materials with a wide coefficient of thermal expansion (CTE) range. Herein we report controllable thermal expansion in the double ReO3-type (Mn1−xNix)ZrF6 solid solutions, whose CTE varies from −4.4 to +15.5 × 10−6 K−1 (300–700 K). In particular, zero thermal expansion has been obtained in the composition of (Mn0.6Ni0.4)ZrF6. (Mn1−xNix)ZrF6 exhibits full solid solution character. The thermal expansion of (Mn1−xNix)ZrF6 is adjusted by the flexibility of the atomic linkages, which is confirmed by the technique of temperature-dependent high-energy synchrotron X-ray pair distribution function.

Zero thermal expansion (ZTE) behavior is rare but important for both fundamental studies and practical applications of functional materials. Until now, most available ZTE materials are either electrical insulating oxides or conductive metallic compounds. Very few ZTE materials exhibit the semiconductor feature. Here we report a ZTE in a semiconducting ferroelectric of 0.6PbTiO3–0.4Bi(Co0.55Ti0.45)O3−δ. Its unit cell volume exhibits a negligible change over a broad temperature range from room temperature to 500 °C. The ZTE is supposed to be correlated with the spontaneous volume ferroelectronstriction. Intriguingly, the present ZTE material also exhibits the semiconducting characteristic accompanied by negative temperature coefficient of resistance. The mechanism of electric conduction is attributed to the electronic hopping from one ion (Ti3+) to another (Ti4+). The semiconductor nature has also been confirmed by the noticeable visible-light absorption with the relatively lower band gap (Eg) value of 1.5 eV, while the ferroelectric property can be well-maintained with large polarization. The first-principles calculations reveal that the drastically narrowed Eg is related to the Co–Ti substitution. The present multifunctional material containing ZTE, semiconducting, and ferroelectric properties is suggested to enable new applications such as the substrate for solar conversion devices.

AbstractThe control of thermal expansion of solid compounds is intriguing but remains challenging. The effect of guests on the thermal expansion of open-framework structures was investigated. Notably, the presence of guest ions (K+) and molecules (H2O) can substantially switch thermal expansion of YFe(CN)6 from negative (αv=−33.67×10−6 K−1) to positive (αv=+42.72×10−6 K−1)—a range that covers the thermal expansion of most inorganic compounds. The mechanism of such substantial thermal expansion switching is revealed by joint studies with synchrotron X-ray diffraction, X-ray absorption fine structure, neutron powder diffraction, and density functional theory calculations. The presence of guest ions or molecules plays a critical damping effect on transverse vibrations, thus inhibiting negative thermal expansion. An effective method is demonstrated to control the thermal expansion in open-framework materials by adjusting the presence of guests.

AbstractThe control of thermal expansion of solid compounds is intriguing but remains challenging. The effect of guests on the thermal expansion of open-framework structures was investigated. Notably, the presence of guest ions (K+) and molecules (H2O) can substantially switch thermal expansion of YFe(CN)6 from negative (αv=−33.67×10−6 K−1) to positive (αv=+42.72×10−6 K−1)—a range that covers the thermal expansion of most inorganic compounds. The mechanism of such substantial thermal expansion switching is revealed by joint studies with synchrotron X-ray diffraction, X-ray absorption fine structure, neutron powder diffraction, and density functional theory calculations. The presence of guest ions or molecules plays a critical damping effect on transverse vibrations, thus inhibiting negative thermal expansion. An effective method is demonstrated to control the thermal expansion in open-framework materials by adjusting the presence of guests.

Piezoelectric materials are considered an enabling technology generating an annual turnover of about 20 billion $. At present, lead-based materials dominate the market with the known risk to health and environment. One of the three key competitors for their replacement is the class of sodium bismuth titanate (NBT)-based relaxor ferroelectrics, the use of which is limited by thermal depolarization. An increased thermal stability has recently been experimentally demonstrated for composites of Na1/2Bi1/2TiO3-6BaTiO3 with ZnO inclusions (NBT-6BT:xZnO). However, the exact mechanism for this enhancement still remains to be clarified. In this study, piezoresponse force microscopy and 23Na NMR spectroscopy were used to demonstrate that the incorporation of ZnO leads to a stabilization of the induced ferroelectric state at room temperature. Temperature-dependent measurements of the relative dielectric permittivity ε′(T), the piezoelectric coefficient d33 and the strain response revealed an increase of the working temperature by 37 °C. A simple mechanics model suggests that thermal deviatoric stresses stabilize the ferroelectric phase and increase, as well as broaden, the temperature range of depolarization. Our results reveal a generally applicable mechanism of enhancing phase stability in relaxor ferroelectric materials, which is also valid for phase diagrams of other ceramic matrix composites.Download high-res image (347KB)Download full-size image

The understanding of the negative thermal expansion (NTE) mechanism remains challenging but critical for the development of NTE materials. This study sheds light on NTE of ScF3, one of the most outstanding materials with NTE. The local dynamics of ScF3 has been investigated by a combined analysis of synchrotron-based X-ray total scattering, extended X-ray absorption fine structure, and neutron powder diffraction. Very interestingly, we observe that (i) the Sc–F nearest-neighbor distance strongly expands with increasing temperature, while the Sc–Sc next-nearest-neighbor distance contracts, (ii) the thermal ellipsoids of relative vibrations between Sc–F nearest-neighbors are highly elongated in the direction perpendicular to the Sc–F bond, indicating that the Sc–F bond is much softer to bend than to stretch, and (iii) there is mainly dynamically transverse motion of fluorine atoms, rather than static shifts. These results are direct experimental evidence for the NTE mechanism, in which the rigid unit is not necessary for the occurrence of NTE, and the key role is played by the transverse thermal vibrations of fluorine atoms through the “guitar-string” effect.

The controllable isotropic thermal expansion with a broad coefficient of thermal expansion (CTE) window is intriguing but remains challenge. Herein we report a cubic MZrF6 series (M = Ca, Mn, Fe, Co, Ni and Zn), which exhibit controllable thermal expansion over a wide temperature range and with a broader CTE window (−6.69 to +18.23 × 10–6/K). In particular, an isotropic zero thermal expansion (ZTE) is achieved in ZnZrF6, which is one of the rarely documented high-temperature isotropic ZTE compounds. By utilizing temperature-dependent high-energy synchrotron X-ray total scattering diffraction, it is found that the flexibility of metal···F atomic linkages in MZrF6 plays a critical role in distinct thermal expansions. The flexible metal···F atomic linkages induce negative thermal expansion (NTE) for CaZrF6, whereas the stiff ones bring positive thermal expansion (PTE) for NiZrF6. Thermal expansion could be transformed from striking negative, to zero, and finally to considerable positive though tuning the flexibility of metal···F atomic linkages by substitution with a series of cations on M sites of MZrF6. The present study not only extends the scope of NTE families and rare high-temperature isotropic ZTE compounds but also proposes a new method to design systematically controllable isotropic thermal expansion frameworks from the perspective of atomic linkage flexibility.

Lead-free piezoelectrics have attracted increasing attention because of the awareness of lead toxicity to the environment. Here, a new bismuth-based lead-free perovskite, (1 – x)Bi(Zn0.5Ti0.5)O3-xBiFeO3, has been synthesized via a high-pressure and high-temperature method. It exhibits interesting properties of giant polarization, morphotropic phase boundary (MPB), and monoclinic phase. In particular, large tetragonality (c/a = 1.228) and giant spontaneous polarization of 110 μC/cm2 has been obtained in 0.6 Bi(Zn0.5Ti0.5)O3-0.4BiFeO3, which is much higher than most available lead-free materials and conventional Pb(Zr,Ti)O3. MPB is clearly identified to be constituted of tetragonal and monoclinic phases at x = 0.5. Notably, a single monoclinic phase has been observed at x = 0.6, which exhibits an intriguing high-temperature property. The present results are helpful to explore new lead-free MPB systems in bismuth-based compounds.

The destructive readout signal distinguishing the ferroelectric polarization state in a memory device has long been seen as the bottleneck for its commercial application. Both ferroelectric resistive switching and the switchable photovoltaic effect provide multiple choices for non-destructive readout. The polycrystalline ferroelectric BiFeO3-based thin films fabricated by cost-effective chemical solution growth exhibit large resistive switching (with ON/OFF ratios ∼104), which is comparable to switchable diodes and tunnel junctions. Furthermore, switchable photovoltaic response shows stable switching and good retention properties. The standard hysteretic loops of resistive switching current, short circuit current and open circuit voltage versus poling voltage directly indicate hysteretic modulation by ferroelectric polarization, which is the first evidence in polycrystalline BiFeO3 based films. The present films would be potential candidates for non-destructive ferroelectric memory devices with multiple selections.

Hollow spheres of multicomponent (CuIn)xZn2(1−x)S2 solid solutions have been rapidly synthesized by a salt-assisted aerosol decomposition method. (CuIn)0.2Zn1.6S2 hollow spheres with a band gap of 2.53 eV exhibited an excellent and stable photocatalytic activity of 360 μmol h−1 (50 mg photocatalysts) for hydrogen evolution from aqueous solutions containing sacrificial reagents (SO32− and S2−) under visible light (λ ≥ 420 nm) due to the well-crystallized microspheres and mesoporous structures. H2 evolution rate of the (CuIn)0.2Zn1.6S2 hollow spheres reached as high as 57 μmol h−1 (50 mg photocatalysts) even without Ru loading.

The rare physical property of zero thermal expansion (ZTE) is intriguing because neither expansion nor contraction occurs with temperature fluctuations. Most ZTE, however, occurs below room temperature. It is a great challenge to achieve isotropic ZTE at high temperatures. Here we report the unconventional isotropic ZTE in the cubic (Sc1–xMx)F3 (M = Ga, Fe) over a wide temperature range (linear coefficient of thermal expansion (CTE), αl = 2.34 × 10–7 K–1, 300–900 K). Such a broad temperature range with a considerably negligible CTE has rarely been documented. The present ZTE property has been designed using the introduction of local distortions in the macroscopic cubic lattice by heterogeneous cation substitution for the Sc site. Even though the macroscopic crystallographic structure of (Sc0.85Ga0.05Fe0.1)F3 adheres to the cubic system (Pm3̅m) according to the results of X-ray diffraction, the local structure exhibits a slight rhombohedral distortion. This is confirmed by pair distribution function analysis of synchrotron radiation X-ray total scattering. This local distortion may weaken the contribution from the transverse thermal vibration of fluorine atoms to negative thermal expansion, and thus may presumably be responsible for the ZTE. In addition, the present ZTE compounds of (Sc1–xMx)F3 can be functionalized to exhibit high-Tc ferromagnetism and a narrow-gap semiconductor feature. The present study shows the possibility of obtaining ZTE materials with multifunctionality in future work.

Synthesis of hollow structures of metal sulphides generally involves various templates and complex chemical processing. In the present study, a general and rapid method of salt-assisted aerosol decomposition (SAD) is presented for the synthesis of hollow spheres of various metal sulfides, including ZnS, ternary sulfides, and solid solutions. The NaCl salt plays a critical role in the formation of hollow spheres of metal sulfides. The hollow spherical microstructure was formed from solid by using a small amount of water soluble NaCl salt. The formation of metal sulphide hollow spheres differs from previous mechanisms and is referred to as molten salt heterogeneous nucleation (MSHN). The present method offers the most promising advantage for controlling the multicomponent composition of hollow spheres. Furthermore, hollow spheres of sulphides have much enhanced properties such as photoluminescence of ZnS:Mn2+ and photocatalytic dye degradation of ZnIn2S4 due to the role of molten salt in the promotion of crystallization, The present method could be explored further by applying the process to other compounds such as sulfides, oxides, and nitrides.

Bi(Mg3/8Fe2/8Ti3/8)O3, a member of a small group of pure Bi3+ A site perovskites, exhibiting a high ferroelectric Curie point (Tc), was rapidly synthesized by a sample method of molten salt synthesis. The purity of Bi(Mg3/8Fe2/8Ti3/8)O3 samples is directly affected by the reaction conditions such as the soaking temperature, and the heating and cooling rates. The as-prepared Bi(Mg3/8Fe2/8Ti3/8)O3 particles are well-formed, cube-shaped single-crystals with sizes ranging from 200–300 nm. The chemical states of Bi and Fe ions are Bi3+ and Fe3+ in Bi(Mg3/8Fe2/8Ti3/8)O3. UV-vis diffuse reflectance spectra and preliminary photocatalytic experiments indicate that the pure Bi3+ A site perovskite of Bi(Mg3/8Fe2/8Ti3/8)O3 has a suitable energy bandgap (1.86 eV) and shows obvious photocatalytic activity for the decolorization of methyl blue under visible-light irradiation. The present work suggests potential future applications of Bi(Mg3/8Fe2/8Ti3/8)O3 in photocatalysis and ferroelectric photovoltaic effects.

According to consideration on the average radius of B-site cation of BiMeO3, we reported that the Bi(Mg0.5Zr0.5)O3–xPbTiO3 compound at the morphotropic phase boundary (MPB) of x=0.58 possesses a piezoelectric coefficient d33 as high as 306 pC/N. The optimal piezoelectric and ferroelectric properties near the MPB might be attributed to its lower lattice distortion, as described by change of FWHM value for {1 1 1}PC peaks. Furthermore, Bi(Mg0.5Zr0.5)O3–xPbTiO3 displayed stable ferroelectric and piezoelectric properties over a temperature range from ambient temperature to above 160 °C, as exhibited by temperature dependence polarization and strain versus electric field curves and thermal depoling process.

The experimental electron-density distribution of ferroelectric bismuth ferrite (BiFeO3) has been visualized using the synchrotron X-ray powder diffraction data and the maximum-entropy method. The present work has clearly revealed the partial covalency of the Bi–O bond, which is a key to understand the spontaneous polarization. Density functional theory (DFT) calculation has supported the validity of the experimental results.

The applications of ferroelectric thin films such as the sensitivity of nonvolatile ferroelectric random access memories are closely linked with large remnant polarization. The high-TC (1−x)Bi(Zn1/2Zr1/2)O3–xPbTiO3 (x = 0.7–0.9) thin films with high (100) orientation were fabricated on Pt(111)/Ti/SiO2/Si substrates via a sol–gel method. The thin films could be crystallized well in a phase-pure perovskite structure. The electrical properties of the sol–gel-derived BZZ–PT thin films were investigated. A large remanent polarization with 2Pr up to 110 μC cm−2 and a small leakage current of 3.8 × 10−7 A cm−2 under an electric field of 150 kV cm−1 are observed on the 0.2BZZ–0.8PT thin films. Furthermore, a relatively stable polarization fatigue property was achieved, indicating a potential application in high-temperature ferroelectric devices.

The destructive readout signal distinguishing the ferroelectric polarization state in a memory device has long been seen as the bottleneck for its commercial application. Both ferroelectric resistive switching and the switchable photovoltaic effect provide multiple choices for non-destructive readout. The polycrystalline ferroelectric BiFeO3-based thin films fabricated by cost-effective chemical solution growth exhibit large resistive switching (with ON/OFF ratios ∼104), which is comparable to switchable diodes and tunnel junctions. Furthermore, switchable photovoltaic response shows stable switching and good retention properties. The standard hysteretic loops of resistive switching current, short circuit current and open circuit voltage versus poling voltage directly indicate hysteretic modulation by ferroelectric polarization, which is the first evidence in polycrystalline BiFeO3 based films. The present films would be potential candidates for non-destructive ferroelectric memory devices with multiple selections.

The experimental electron-density distribution of ferroelectric bismuth ferrite (BiFeO3) has been visualized using the synchrotron X-ray powder diffraction data and the maximum-entropy method. The present work has clearly revealed the partial covalency of the Bi–O bond, which is a key to understand the spontaneous polarization. Density functional theory (DFT) calculation has supported the validity of the experimental results.

Bi(Mg3/8Fe2/8Ti3/8)O3, a member of a small group of pure Bi3+ A site perovskites, exhibiting a high ferroelectric Curie point (Tc), was rapidly synthesized by a sample method of molten salt synthesis. The purity of Bi(Mg3/8Fe2/8Ti3/8)O3 samples is directly affected by the reaction conditions such as the soaking temperature, and the heating and cooling rates. The as-prepared Bi(Mg3/8Fe2/8Ti3/8)O3 particles are well-formed, cube-shaped single-crystals with sizes ranging from 200–300 nm. The chemical states of Bi and Fe ions are Bi3+ and Fe3+ in Bi(Mg3/8Fe2/8Ti3/8)O3. UV-vis diffuse reflectance spectra and preliminary photocatalytic experiments indicate that the pure Bi3+ A site perovskite of Bi(Mg3/8Fe2/8Ti3/8)O3 has a suitable energy bandgap (1.86 eV) and shows obvious photocatalytic activity for the decolorization of methyl blue under visible-light irradiation. The present work suggests potential future applications of Bi(Mg3/8Fe2/8Ti3/8)O3 in photocatalysis and ferroelectric photovoltaic effects.

TiO2/CdS porous hollow microspheres have been one-pot rapidly synthesized by a salt-assisted aerosol decomposition method, and exhibit an excellent photocatalytic activity of 996 μmol h−1 (50 mg photocatalysts with loading Ru co-catalyst) for hydrogen evolution from aqueous solutions containing sacrificial reagents (SO32− and S2−) under visible light (λ ≥ 420 nm). Its high photocatalytic performance is attributed to the surface morphology, crystallinity and heterostructures. The present facile method can be extended to fabricate other heterostructures consisting of oxides or sulfides.

Semiconductor functional materials have been widely applied in electronic devices. However, the reliability and lifetime of the devices suffer from the undesirable mismatch of the coefficients of thermal expansion. It is important to develop semiconductor materials with controllable thermal expansion. Here, we develop a remarkable group of ferroelectric semiconductor materials (1 − x)PbTiO3–xBi(Co2/3Nb1/3)O3 (PT–100xBCN) that have not only tunable electronic and optical properties, but also controllable negative, zero, and positive thermal expansion. Through the BCN chemical substitution, the bandgap (Eg) is reduced from 2.60 eV to 2.26 eV to achieve semiconducting properties in PbTiO3-based ferroelectrics. Meanwhile, we have achieved a gradual transition from negative, to zero, and then to positive thermal expansion (αV: −12.3 × 10−6 to 7.4 × 10−6 K−1). Besides, PT–BCN exhibits ferroelectric and piezoelectric properties. The relatively high piezoelectric coefficient d33 ∼ 200 pC N−1 was achieved in the composition of PT–42BCN near the morphotropic phase boundary. PT–BCN shows good negative temperature coefficient (NTC) thermistor characteristics. The coexistence of light absorption, thermal expansion, and electronic properties in PT–BCN makes it a promising material for future applications. The present study would offer an approach to developing and exploring new multifunctional semiconducting materials with controllable thermal expansion.

Synthesis of hollow structures of metal sulphides generally involves various templates and complex chemical processing. In the present study, a general and rapid method of salt-assisted aerosol decomposition (SAD) is presented for the synthesis of hollow spheres of various metal sulfides, including ZnS, ternary sulfides, and solid solutions. The NaCl salt plays a critical role in the formation of hollow spheres of metal sulfides. The hollow spherical microstructure was formed from solid by using a small amount of water soluble NaCl salt. The formation of metal sulphide hollow spheres differs from previous mechanisms and is referred to as molten salt heterogeneous nucleation (MSHN). The present method offers the most promising advantage for controlling the multicomponent composition of hollow spheres. Furthermore, hollow spheres of sulphides have much enhanced properties such as photoluminescence of ZnS:Mn2+ and photocatalytic dye degradation of ZnIn2S4 due to the role of molten salt in the promotion of crystallization, The present method could be explored further by applying the process to other compounds such as sulfides, oxides, and nitrides.

The applications of ferroelectric thin films such as the sensitivity of nonvolatile ferroelectric random access memories are closely linked with large remnant polarization. The high-TC (1−x)Bi(Zn1/2Zr1/2)O3–xPbTiO3 (x = 0.7–0.9) thin films with high (100) orientation were fabricated on Pt(111)/Ti/SiO2/Si substrates via a sol–gel method. The thin films could be crystallized well in a phase-pure perovskite structure. The electrical properties of the sol–gel-derived BZZ–PT thin films were investigated. A large remanent polarization with 2Pr up to 110 μC cm−2 and a small leakage current of 3.8 × 10−7 A cm−2 under an electric field of 150 kV cm−1 are observed on the 0.2BZZ–0.8PT thin films. Furthermore, a relatively stable polarization fatigue property was achieved, indicating a potential application in high-temperature ferroelectric devices.

It is an interesting but challenge issue to prepare isotropic controllable thermal expansion materials with a wide coefficient of thermal expansion (CTE) range. Herein we report controllable thermal expansion in the double ReO3-type (Mn1−xNix)ZrF6 solid solutions, whose CTE varies from −4.4 to +15.5 × 10−6 K−1 (300–700 K). In particular, zero thermal expansion has been obtained in the composition of (Mn0.6Ni0.4)ZrF6. (Mn1−xNix)ZrF6 exhibits full solid solution character. The thermal expansion of (Mn1−xNix)ZrF6 is adjusted by the flexibility of the atomic linkages, which is confirmed by the technique of temperature-dependent high-energy synchrotron X-ray pair distribution function.

Hollow spheres of multicomponent (CuIn)xZn2(1−x)S2 solid solutions have been rapidly synthesized by a salt-assisted aerosol decomposition method. (CuIn)0.2Zn1.6S2 hollow spheres with a band gap of 2.53 eV exhibited an excellent and stable photocatalytic activity of 360 μmol h−1 (50 mg photocatalysts) for hydrogen evolution from aqueous solutions containing sacrificial reagents (SO32− and S2−) under visible light (λ ≥ 420 nm) due to the well-crystallized microspheres and mesoporous structures. H2 evolution rate of the (CuIn)0.2Zn1.6S2 hollow spheres reached as high as 57 μmol h−1 (50 mg photocatalysts) even without Ru loading.