The average measured Hv for polycrystalline ReB2 and Ti–B composites under different loads shows that the tendency of Hv to decrease becomes weak for large loads, and the measured hardness of ReB2 is always lower than that of Ti–B composites. For comparison, the results from Chung et al. were inserted into the figure.

No abstract

The electrical conductivity of shock-compressed iron was measured up to 208 GPa by using an improved sample assembly in which the iron sample is encapsulated in a single-crystal sapphire cell. High-pressure shock compressions were generated by plate impact with a two-stage light-gas gun. The measured conductivity of iron varies from 1.45 × 104 Ω −1 cm−1 at 101 GPa and 2010 K, to 7.65 × 103 Ω−1 cm−1 at 208 GPa and 5220 K. After analysing these data together with those reported previously, we found that the Bloch–Grüneisen expression is valid for ε-iron in the pressure and temperature range up to 208 GPa and 5220 K.

Multimetal doping is a promising strategy to achieve high-performance electrocatalysts for the oxygen evolution reaction (OER) due to synergistic effects; however, understanding the dynamic structure evolution and clarifying the catalytic mechanism of each individual doping metal in multimetal-based electrocatalysts remain elusive. Here, we report the synthesis of homogeneous single-metal and bimetal doping sulfides with a pyrite structure for OER catalysts via a high-pressure and high-temperature (HPHT) technique; operando Raman and X-ray absorption spectroscopy (XAS) studies are performed to capture the dynamic evolution during the OER process. Our results find that an Fe- and Ni-codoped CoS2 electrocatalyst exhibits significantly improved OER activity with an overpotential of 242 (295) mV at 10 (100) mA cm–2 and robust stability over 500 h in an alkaline medium. Operando analysis reveals that Fe and Ni incorporations not only expedite the dynamic response of self-reconstructions of the Fe,Ni-CoS2 surface but also accelerate the oxidation of Co and Fe into high-valence oxyhydroxides while suppressing nickel oxidation to form Ni­(OH)2 for optimized activity and robust stability. This finding provides a fundamental understanding of the composition design, dynamic reaction pathways, and controlling principle for highly active multimetal-based OER catalysts.

The discovery of electrides, in particular, inorganic electrides where electrons substitute anions, has inspired striking interests in the systems that exhibit unusual electronic and catalytic properties. So far, however, the experimental studies of such systems are largely restricted to ambient conditions, unable to understand their interactions between electron localizations and geometrical modifications under external stimuli, e.g., pressure. Here, pressure‐induced structural and electronic evolutions of Ca2N by in situ synchrotron X‐ray diffraction and electrical resistance measurements, and density functional theory calculations with particle swarm optimization algorithms are reported. Experiments and computation are combined to reveal that under compression, Ca2N undergoes structural transforms from R 3true¯ m symmetry to I 4true¯2d phase via an intermediate Fd 3true¯ m phase, and then to Cc phase, accompanied by the reductions of electronic dimensionality from 2D, 1D to 0D. Electrical resistance measurements support a metal‐to‐semiconductor transition in Ca2N because of the reorganizations of confined electrons under pressure, also validated by the calculation. The results demonstrate unexplored experimental evidence for a pressure‐induced metal‐to‐semiconductor switching in Ca2N and offer a possible strategy for producing new electrides under moderate pressure.

High-energy synchrotron x-ray diffraction was utilized to study the local order of liquid sulfur at high-pressure and high-temperature conditions. A temperature driven structure change in liquid sulfur was observed, signified by an order of magnitude reduction in lengths of sulfur chains. The large change in chain length implies that this is a liquid-liquid phase transition in sulfur. The chain breakage may strongly influence the physical properties, such as the semiconductor-metal transition and a drastic decrease in viscosity across the transition.

No abstract

We present a simple but accurate scheme to compute the thermodynamic properties of crystalline solids in a wide range of pressure and temperature based on ab initio calculations. Compared to the method based on ab initio thermodynamic-integration techniques, our approach can reduce dramatically the number of ab initio molecular-dynamics simulations needed in the calculations of the intrinsic anharmonic effect neglected in the conventional quasiharmonic approximation. Taking tungsten as an example, we show that its thermal properties including the linear thermal-expansion coefficient and the equation of state ͑EOS͒ at high pressures and temperatures can be calculated accurately. The precise EOS of W for the pressure up to 500 GPa and the temperature up to 10 000 K may serve as a pressure scale. This method may be able to be extended to the study of solid-solid phase transitions of various crystalline solids, including some alloys.