A multihierarchical structure with (NH4)(Ni, Co)PO4·0.67H2O microplatelets and (Ni, Co)3(PO4)2·8H2O ultrathin nanopieces anchored on reduced graphene oxide (NCNP/RGO) is synthesized via a mild hydrothermal approach. This unique interface-rich structure is suitable for a high power energy storage device by providing efficient pathways for both electronic conduction and ionic transportation, which are effective ways to improve the electrochemical performance. Specifically, a specific capacity of 993 F g–1 is obtained in the three-electrode measurement, with ultrahigh capacity retention of 81.2% (807 F g–1) from 0.5 to 32 A g–1. The hybrid device constructed with the as-prepared NCNP/RGO as anode and a hierarchical porous carbon (HPC) as cathode offers a very superior energy density of 42.1 Wh kg–1 at a power density of 73 W kg–1, which remains 32 Wh kg–1 at 14 kW kg–1. Meanwhile, the as-prepared hybrid capacitor exhibits a remarkable cycling stability (96.5% capacitance retention after 10 000 cycles). The capacity contribution of capacitive behavior for the hybrid device is analyzed as 91.1% at 25 mV s–1.Keywords: High power; Hybrid energy storage; Multihierarchical; Phosphate;

•Two-dimensional porous sheet-like carbon-doped ZnO/g-C3N4 nanocomposites were synthesized.•The absorbance intensity in the visible light region is enhanced with the hybridization of g-C3N4.•Carbon-doped ZnO/g-C3N4 show improved visible light photocatalytic activity.The ZnO/g-C3N4 nanocomposites were synthesized by a single-step and scalable synthesis method through calcining the mixture of zinc acetate and urea. Two-dimensional shape, porous and carbon-doped microstructure were demonstrated by the SEM, TEM, N2 adsorption and XPS. ZnO/g-C3N4 nanocomposites were used as a photocatalyst for photodegradation of MB and MO under visible light irradiation. The photocatalytic performance of the porous sheet-like carbon-doped ZnO/g-C3N4 nanocomposites was higher than those of commercial P25, ZnO and g-C3N4.

•Ni-W/diamond composite coatings were prepared by direct current electrodeposition.•The diamond content in the deposits can enhance the mechanical properties of the coatings.•Diamond particle size affects the mechanical properties and the diamond content in the deposits.Ni-W/diamond composite coatings were prepared by electrodeposition from a Ni-W plating bath with diamond particles suspended into the bath. The effect of the plating parameters on microstructure and mechanical properties was investigated. The deposits reported a maximum hardness of 1207 ± 32 Hv. The film hardness is depended on the concentration of diamond particles in the plating bath and also on the size of the co-deposited diamond particles. The sample with diamond concentration of 10 g/L in the bath and co-deposited at current density of 0.15 A/cm2 reported the optimized wear resistance and diamond content in the deposit. In this paper the effect of the incorporation of diamond particles into the Ni-W matrix has been discussed in terms of the aforesaid operating conditions and particle size.

•C-TiO2/g-C3N4 heterojunction were fabricated via in situ heat treatment.•C-TiO2 nanoparticles anchor on the surface of the g-C3N4.•C-TiO2/g-C3N4 photocatalysts exhibit superior photocatalytic activity.•C-TiO2/g-C3N4 photocatalysts possess excellent photostability.Graphitic carbon nitride (g-C3N4) photocatalysts have attracted much attention towards harvesting solar energy for applications in energy and environment sectors. However, separation of electron-hole pairs is an intrinsic problem for the bulk g-C3N4. Here, we report the tiny amount of carbon doped TiO2 modified g-C3N4 (C-TiO2/g-C3N4) with a narrow bandgap and prolonged lifetime of charge carriers. This heterojunction photocatalysts were successfully fabricated via a facile heat treatment under atmosphere. The enhanced separation of photogenerated charge carriers and narrow band gap confer superior photocatalytic activities with 5.728 mmol/g photogenerated hydrogen gas for 5 h and 52.395 mmol/g for 64 h in triethanolamine aqueous solution. The apparent quantum efficiency of C-TiO2/g-C3N4 is ~ 6.2% under 420 nm irradiation, which is about 2.4 times higher than the corresponding value 2.6% of pristine g-C3N4. This photocatalyst with excellent photocatalytic performance and photo-stability can work as a promising candidate to applicate in solar-to-fuel conversion and environmental remediation.Download high-res image (224KB)Download full-size image

In this paper, the microstructural evolution and mechanical properties of the as-cast Ti-χZr-4Al-0.005B (TχZAB and χ=0, 10, 20, 30, 40 wt%) alloys were systematically investigated. Only the α phase was detected from the X-ray diffraction patterns of the as-cast TχZAB quaternary alloy series. As the Zr content increased, the average size and length-diameter ratio of the α grains were decreased from 69.8 μm to 17.1 µm and 37.5 to 8.4, respectively. The analysis of the results from the tensile and microhardness tests demonstrated that both the strength and hardness increased significantly as the Zr content increased (from 0 wt% to 40 wt%). Nevertheless, the ductility exhibited an opposite trend. The fracture mode of the ductile-brittle transfer was consistent with the ductility alteration. The as-cast Ti-40Zr-4Al-0.005B alloys demonstrated the highest tensile strength (σb=1134 MPa), which increased by 53% compared to the Ti-4Al-0.005B alloys, whereas the lowest elongation-to-failure was of 6.77%. The mechanical properties of the TχZAB alloy series were discussed based on the microstructural evolution and the solid solution strengthening mechanisms.

•The content of β phase increased as the V addition increased.•Heterogeneous lamella structure was obtained by the addition of V traces.•As V content increased, the strength and ductility of ZrV alloys were improved.The phase composition and mechanical properties of several ZrV alloys with various V contents were studied to achieve an improved balance of strength and ductility of Zr alloy. The heterogeneous lamella structure including the coarse initial α phase, the ultrafine β phase and the acicular α′ martensite phase was obtained by the addition of V traces. As the V content increased (from 0 to 0.5 wt%), the strength and ductility of ZrV alloys were apparently improved. It was confirmed that the strength was strongly affected not only by the solid solution strengthening of the V atoms, but also by the formation of heterogeneous lamella structure due to the V addition. In addition, the β phase content increases and the existence of near-spherical initial α grains with lower dislocation density could effectively enhance the Zr0.5V alloy ductility.

•Pitting corrosion behaviour of novel Zr-40Ti-5Al–4 V alloy was investigated.•Crystallographic pitting was observed in the single-phase β-Zr alloy.•Pitting of the double-phase Zr alloy is isotropic and circular in shape.•Double-phase Zr alloy is more sensitive to pitting than the single-phase alloy.Pitting corrosion behaviour of Zr-40Ti-5Al–4 V alloys with different phase composition was investigated. Pitting of the single-phase β-Zr alloy is crystallographic and the corrosion pits exhibit different orientation, which is mainly attributed to the favored dissolution kinetics of the {001} plane in body-centered cubic β grains. In contrast, isotropic and circular shaped pitting, due to the evenly distributed α and β phases, was observed in Zr alloy containing α + β double-phase. In addition, weight loss and electrochemical experiments reveal that the double-phase alloy is more sensitive to pitting than the single-phase alloy.Download high-res image (653KB)Download full-size image

•Distinct H absorption behavior of ZrPd2 and Zr2Pd is unusual given their similarity.•We propose an electron density origin of their distinct H absorption behavior.•ZrPd2 and Zr2Pd actually possess different electron density topologies.•Pseudoatom in Zr2Pd renders it isostructural with Zr2PdH2, favoring H absorption.•Formation of ZrPd2H2 requires change in topological structure, while ZrPd2H2 doesn't.Hydrogen (H) interaction with metals and alloys is of intense interest in a span of topics in materials science and engineering. Distinct H absorption behavior of two similar intermetallic compounds, namely, Zr2Pd and ZrPd2, is not clearly elucidated in terms of their common MoSi2-type structure and hydride-forming constituents. This work addresses that extended structures (electron density topologies) of these compounds are actually different, which causes the different properties they possess. Pseudoatoms manifested by non-nuclear maxima of electron density are uncovered in Zr2Pd's Zr tetrahedral interstices, whereas atoms in ZrPd2 are bonded through straight bond paths. Interstitial pseudoatoms, which are characterized by a weak localization nature revealed by Laplacian calculations, readily lose excess charges to H. Therefore, these properties favor formation of covalent–ionic Zr–H bonding and concurrent H absorption. During Zr2PdH2 formation, the entire topological structure of Zr2Pd is retained; by contrast, ZrPd2H2 formation requires charge redistribution of the stable host lattice of ZrPd2 to change electron density topology and hence is endothermic and unfavorable. The present work reveals a concrete and visualized origin of the distinct H absorption behaviors of the two similar compounds, which has implications in the search for new H-related materials.

•A biomorphic porouscarbon was synthesized using a mold as the precursor.•The electrode exhibits an ultra high volumetric capacitance up to 655 F cm−3.•The electrode displays superior cycle stability of 100% after 10,000 cycles.A novel biomorphic heteroatom-doped porous carbon with 2.86% of nitrogen and 12.36% of oxygen is synthesized by using a mold (Rhizoctonia Solani Kuhn) as the precursor. The biomorphic porous carbon electrode material exhibits an ultra-high volumetric capacitance of up to 655 F cm−3 at current density of 0.5 A g−1 and superior cycle stability of 100% after 10,000 cycles at a current density of 10 A g−1. This work provides a new approach to obtain biomass with low cost, no pollution, short production cycle and high yield. Furthermore, the genetic stability is more beneficial for the formation of the uniform architecture and composition.

With the aim to develop new Zr-based alloys with excellent mechanical properties, a novel Zr-0.8B (wt%) alloy was manufactured through the following steps: casting, forging, hot-rolling and annealing treatment. The microstructure and mechanical properties of the hot-rolled and annealed Zr-0.8B alloys were investigated. The microstructure of all specimens was comprised by α and ZrB2 phases. The coarse α laths and ZrB2 whiskers were significantly refined by hot rolling. Also, a high volume of dislocations and many subgrains were formed during the hot-rolling process. A high degree of recrystallization of α phase was obtained during the annealing treatment, due to the substantially stored energy in the Zr matrix and the presence of a significant amount of subgrains. The tensile strength of the annealed Zr-0.8B alloys was decreased with the increase of annealing temperature, until 800 °C, and then increased as the heat treatment temperature was further increased to 900 °C. Many factors, such as the volume fraction of ZrB2 whiskers, grain size, dislocation density, the amount of subgrains and solution strengthening, have a significant effect on the strength. However, the elongation-to-failure showed a reverse tendency compared to the tensile strength. The reasons caused fracture of the annealed Zr-0.8B alloys are primarily attributed to dislocation pile-ups and the presence of microvoids.

The evolution of microstructure and mechanical properties of Zr0.5Be alloy were investigated by varying the annealing temperature. X-ray diffraction results show that the examined Zr alloy is composed of α phase and Be2Zr compound after annealing at temperatures between 600 and 850 °C. The optical and transmission electron microscopy results reveal that the recrystallization volume fraction of the α phase gradually increases with increase in annealing temperature. The mechanical properties of the alloy were also investigated by varying the annealing temperature. It was observed that both the tensile strength and micro-hardness of Zr0.5Be alloy gradually decrease with increase in annealing temperature, while the elongation-to-failure increases at higher annealing temperatures. The decrease in dislocation density, the increase in recrystallization volume fraction of the α phase, and distribution of compounds were largely responsible for the decreased tensile strength and micro-hardness and improved ductility of the examined alloys. This work provides a better understanding of the mechanical properties of Zr alloys and helps pave the path for their further development.

•Phase competition between C11b, C16 and E93 phases in Zr2Cu1−xNix is studied.•The E93 phase is less competitive than the C11b and C16 ones.•External pressure as well as increasing Ni content stabilizes the C16 phase.•Some phenomena in crystallization of related BMGs find rationalization.•Design of BMG composites with tunable precipitates is proposed accordingly.Phase competition between C11b, C16 and E93 phases under pressure (0–60 GPa) in Zr2Cu1−xNix (x = 0, 0.125, 0.25, 0.50, 0.75, 0.875 and 1) alloys has been investigated by first-principles pseudopotential calculations. The whole picture of phase competition mediated by both external pressure and composition has been unambiguously established by modeling using both supercell (SC) method and virtual crystal approximation (VCA) method, which sheds light on the pressure dependent glass stability and crystallization behavior of related alloy systems. It is revealed that both pressure and increasing Ni content stabilize the C16 phase over the other two. The underlying mechanism of external pressure and composition stabilizing the C16 phase is also analyzed. A feasible procedure for achieving metallic glass composites with tunable precipitated phases is proposed.

The recently predicted ZrB4 with an Amm2 orthorhombic structure has great scientific and technical significance owing to its novel B–Zr–B “sandwich” layer bonding and evaluated high hardness. To better understand the performance of Amm2-ZrB4, its elastic and thermodynamic properties under pressure and temperature are studied here by taking advantage of first principles calculations in combination with the quasi-harmonic Debye model. It is found that ZrB4 keeps brittleness and mechanical stability up to 100 GPa, possessing pronounced elastic anisotropy demonstrated by the elastic anisotropy factors, the direction-dependent Young's modulus, shear modulus and Poisson's ratio. The pressure and temperature dependences of the thermodynamics parameters including normalized volume V/V0, bulk modulus, specific heat, Debye temperature, thermal expansion coefficient and Grüneisen parameter in wide temperature (0–1000 K) and pressure (0–50 GPa) ranges are obtained and discussed in detail.

Structural, elastic, electronic and thermodynamic properties of ZrSi2 have been investigated by means of first-principles plane wave pseudopotential calculations combined with the quasi-harmonic Debye model. We find that the orthorhombic base-centered lattice structure (C49) ZrSi2 is mechanically stable up to 80 GPa according to the elastic stability criteria, and there is a transition from brittle to ductile nature at about 56.5 GPa. The calculated elastic anisotropy factors suggest that ZrSi2 is anisotropic and the degree increases with pressure. In addition, the bonding characteristics are discussed by analyzing the energy band structure, charge density distribution and Mulliken populations. The pressure and temperature dependences of the bulk modulus, specific heat, Debye temperature and thermal expansion coefficient are also discussed through the quasiharmonic Debye model.

•New ternary CdxMg1−xS materials are designed.•Electronic, optical and thermodynamic properties are theoretically determined.•The stable, metastable and unstable regions are obtained by the calculated T–x phase diagram.The structural, electronic, optical and thermodynamic properties of CdxMg1−xS (0 ⩽ x ⩽ 1) alloys in rock-salt phase have been investigated using first-principles method based on density functional theory. Our calculated lattice constants and bulk moduli for MgS and CdS are in good agreement with the available theoretical and experimental data. The lattice constants increase while the bulk modulus decreases with Cd concentration increasing. The calculated band structure shows that all considered compounds are indirect gap semiconductors. The density of states and optical constants such as complex dielectric function, extinction coefficient, refractive index and absorption coefficient are also calculated and analyzed in detail. Moreover, the thermodynamic stability of these alloys is investigated by the calculated T–x phase diagram.

•Theoretical study of structural stability of WC under high pressure.•Mechanical properties of WC are investigated by first-principle calculations.•Elastic anisotropy of WC in the three structures upto 100 GPa is discussed in detail.The structural stability and mechanical properties of WC in WC-, MoC- and NaCl-type structures under high pressure are investigated systematically by first-principles calculations. The calculated equilibrium lattice constants at zero pressure agree well with available experimental and theoretical results. The formation enthalpy indicates that the most stable WC is in WC-type, then MoC-type finally NaCl-type. By the elastic stability criteria, it is predicted that the three structures are all mechanically stable. The elastic constants Cij, bulk modulus B, shear modulus G, Young׳s modulus E and Poisson׳s ratio ν of the three structures are studied in the pressure range from 0 to 100 GPa. Furthermore, by analyzing the B/G ratio, the brittle/ductile behavior under high pressure is assessed. Moreover, the elastic anisotropy of the three structures up to 100 GPa is also discussed in detail.

•The mechanical and electronic properties of Rh and Rh3Zr are compared in detail.•Rh3Zr has lower mechanical strength but higher ductility than Rh.•Rh (Zr)-d electrons in Rh3Zr become localized (delocalized) than in pure bulk.To give insight on developing Rh-based superalloys, systematic investigations on mechanical and electronic properties of fcc Rh and L12 Rh3Zr are conducted by first-principles calculation. Basic mechanical parameters including bulk modulus, elastic constants, shear modulus, Young׳s modulus, Poisson׳s ratio, and elastic anisotropy are calculated. Additionally, the ideal strengths are investigated under tensile and shear loading. Our results reveal that L12 Rh3Zr has lower mechanical strength but higher ductility than fcc Rh. The analysis of density of states reveals that the Rh-d electrons in L12 Rh3Zr become more localized, whereas the Zr-d electrons become more delocalized, than in pure bulk, due to the interaction of Rh and Zr.

•Structural, elastic and electronic properties of Rh–Zr compounds are investigated.•Of the eleven considered candidate structures, Rh4Zr3 is most stable.•The analysis excludes the presence of Rh2Zr-C37 and RhZr4-D1a at low temperature.•Electronic structure analysis is implemented to understand the essence of stability.A systematic investigation on structural, elastic and electronic properties of Rh–Zr intermetallic compounds is conducted using first-principles electronic structure total energy calculations. The equilibrium lattice parameters, enthalpies of formation (Efor), cohesive energies (Ecoh) and elastic constants are presented. Of the eleven considered candidate structures, Rh4Zr3 is most stable with the lowest Efor. The two orthogonal-type, relative to the CsCl-type, are the competing ground-state structures of RhZr. The result is in agreement with the experimental reports in the literature. The analysis of Efor and mechanical stability excludes the presence of Rh2Zr and RhZr4 at low temperature mentioned by .Curtarolo et al. [Calphad 29, 163 (2005)]. It is found that the bulk modulus B increases monotonously with Rh concentration, whereas all other quantities (shear modulus G, Young's modulus E, Poisson's ratio σ and ductility measured by B/G) show nonmonotonic variation. RhZr2 exhibits the smallest shear/Young's modulus, the largest Poisson's ratio and ductility. Our results also indicate that all the Rh–Zr compounds considered are ductile. Furthermore, the detailed electronic structure analysis is implemented to understand the essence of stability.

•We systematically investigate three competing structures of intermetallic Zr2Cu.•Zr2Cu probably undergoes a phase transition (C11b to C16) under pressure.•All three phases possess a mixed bonding with considerable ionic character.•All three phases have similar Zr–Cu bonding yet distinct Zr–Zr bonding.•C11b Zr2Cu has pseudoatom bonding, while C16 bifurcated bonding.Three competing structures (C11b, C16 and E93) of intermetallic Zr2Cu have been systematically investigated by first-principles calculations and quasi-harmonic Debye model. Both the calculated equation of states (EOS) and pressure–enthalpy results indicate a structural phase transition from C11b to C16 phase at around 11–14 GPa. The calculated equilibrium crystal parameters and elastic constants are in consistence with available experimental or theoretical data. All three phases are mechanically stable according to the elastic stability criteria, and ductile according to Pugh's ratio, while the ambient-stable C11b phase shows a higher elastic anisotropy. Furthermore, differences in the nature of bonding between three competing structures are uncovered by electron density topological analysis. C11b Zr2Cu possesses an intriguing pseudo BaFe2As2-type structure with the charge density maxima at Zr tetrahedral interstices serving as Fe-position pseudoatoms; C16 Zr2Cu contains Zr-pair configurations bonded through bifurcated Zr–Zr bonding paths; while the E93 phase has only conventional straight bonding. Additionally, through quasi-harmonic Debye model, the pressure and temperature dependences of the bulk modulus, specific heat, Debye temperature, Grüneisen parameter and thermal expansion coefficient for three phases are obtained and discussed.

Using the first-principles calypso algorithm for crystal structure prediction, we have predicted two orthorhombic Cmcm and Amm2 structures of ZrB4, which are energetically much superior to the previously proposed WB4-, CrB4-, and MoB4-type structures and stable against decompression into a mixture of Zr and B at ambient pressure. The two orthorhombic structures consist of a hexagonal B ring and ZrB12 units connected by edges and one hexagonal B ring in Cmcm and Amm2 structure, respectively. The calculated large shear modulus (e.g., 229 GPa) and high hardness (42.8 GPa for Cmcm and 42.6 GPa for Amm2) reveal that they are potentially superhard materials. The high hardness is attributed to a stacking of B–Zr–B “sandwiches” layers linked by strong covalent B–B bonding.

•WC-type WN should be metastable which is different from the experimental result.•The predicted NiAs-type WN is an ultra-incompressible and hard material.•WC-type WN possesses ductility nature in the pressure range of 0–80 GPa.•NiAs-type WN has brittle nature in the pressure range of 0–80 GPa.•WN phases are elastically highly anisotropic and dependent on propagation direction.The first-principles study on the structure and mechanical properties of tungsten mononitride (WN) with WC-, NiAs-, and NaCl-structure phases are reported using the pseudopotential plane wave method within the generalized gradient approximation. The obtained equilibrium structure parameters and ground state mechanical properties are in good agreement with the experimental and other theoretical results. The formation enthalpy and elastic stability criteria indicate that NiAs-type WN is always the most energy favorable and mechanical stable phase under current studied pressure range, while the WC-type WN should be metastable which is different from the experimental result. The mechanical properties show that the predicted NiAs-type WN is an ultra-incompressible and hard material among the considered phases. In addition, the calculated B/G ratio indicated that WC-type WN possesses ductility nature and NiAs-type WN has brittle nature in the pressure range of 0–80 GPa. The elastic anisotropic factors for three phases of WN suggest that they are elastically highly anisotropic and strongly dependent on the propagation direction.Graphical abstract

•Porous carbon-doped TiO2 on TiC nanostructures were designed and synthesized.•The obtained catalysts exhibit enhanced charge separation efficiency.•The nanostructures show improved visible light photocatalytic H2 generation.•C-doped and TiC cores can significantly shift the position of the band-edge TiO2.Titanium dioxide (TiO2) has been widely investigated as a photocatalyst material because of its stability and hypotoxicity. However, the photocatalytic activity of TiO2 is suppressed by the large band gap and the high recombination rate of the charge carrier, which leads to confined application. Moreover, how to improve photocatalytic H2 production without any co-catalyst remains a big challenge. Here, we report a conceptual strategy in a core–shell nanostructure of simultaneously reducing the band gap and the charge carrier recombination rate by introducing a carbon-doped porous TiO2 layer onto a metallic TiC nanostructure using a facile in situ thermal growth method. TiC@C-TiO2 core–shell nanostructure materials have higher photocatalytic activity in methanol aqueous solution than those of pure P25 and carbon-doped TiO2, which results from enhanced visible light absorption, drastic charge transfer, and the large surface area. Notably, the novel core–shell nanostructures still exhibit excellent photocatalytic H2 production without Pt co-catalyst. The results demonstrate that TiC is an ideal support for TiO2 photocatalysts, and this novel core–shell nanostructure can significantly shift the position of the band edge of the obtained material. This study presents a design principle for photocatalytic materials as highly efficient visible light photocatalysts.Download high-res image (91KB)Download full-size image

The influence of various Fe contents on the microstructure and mechanical properties of Ti-30Zr-5Al-3V (ZTAV) alloy was investigated. After Fe addition, the grain refinement is obvious and the phase composition changes as α′+β→β. Ti-30Zr-5Al-3V-0.5Fe exhibits a better mechanical property (σb≈1420 MPa, εf≈5.34%) than Ti-30Zr-5Al-3V (σb≈1302 MPa, εf≈4.28%). Highest ultimate tensile strength (σb≈1667 MPa, εf≈2.34%) have been achieved in Ti-30Zr-5Al-3V-1.5Fe. The mechanical properties change owe to the phase transformation, grain refinement, and solid solution strengthening caused by Fe addition.

Using the first-principles calypso algorithm for crystal structure prediction, we have predicted two orthorhombic Cmcm and Amm2 structures of ZrB4, which are energetically much superior to the previously proposed WB4-, CrB4-, and MoB4-type structures and stable against decompression into a mixture of Zr and B at ambient pressure. The two orthorhombic structures consist of a hexagonal B ring and ZrB12 units connected by edges and one hexagonal B ring in Cmcm and Amm2 structure, respectively. The calculated large shear modulus (e.g., 229 GPa) and high hardness (42.8 GPa for Cmcm and 42.6 GPa for Amm2) reveal that they are potentially superhard materials. The high hardness is attributed to a stacking of B–Zr–B “sandwiches” layers linked by strong covalent B–B bonding.