Search

It is unclear whether there is a liquidâ€"liquid phase transition or not in the bismuth melt at high temperature and high pressure. If so, it will be necessary to confirm the boundary of the liquidâ€"liquid phase transition and clarify whether it is a first-order phase transition. Here, based on x-ray absorption spectra and simulations, the temperature dependence of bismuth structures is investigated under different pressures. According to the similarity of characteristic peaks of x-ray absorption near edge structure (XANES) spectra, we estimate the possible temperature ranges of liquidâ€"liquid phase transition to be 779â€"799 K at 2.74 GPa and 859â€"879 K at 2.78 GPa, 809â€"819 K at 3.38 GPa and 829â€"839 K at 3.39 GPa and 729â€"739 K at 4.78 GPa. Using ab initio molecular dynamics (AIMD) simulations, we obtain the stable structures of the bismuth melt at different temperatures and pressures, and calculated their electronic structures. Meanwhile, two stable phases (phase III-like and phase IV-like) of bismuth melts are obtained from different initial phases of bismuth solids (phase III and phase IV) under the same condition (3.20 GPa and 800 K). Assuming that the bismuth melt undergoes a phase transition from IV-like to III-like between 809 K and 819 K at 3.38 GPa, the calculated electronic structures are consistent with the XANES spectra, which provides a possible explanation for the first-order liquidâ€"liquid phase transition. [ABSTRACT FROM AUTHOR]

Fluorite phase CeO2 is compressed non-hydrostatically up to 27 GPa using a diamond anvil cell until the transition to α-PbCl2 phase occurred. The compressive strength (t) of CeO2 as a function of pressure is determined by the line width analysis of the high pressure angle dispersive x-ray diffraction patterns. The strength of CeO2 increases quickly below 3.30 GPa and reaches a plateau region at high pressures. A procedure combined the line width analysis and the line shift analysis together, based on the non-hydrostatic data to obtain the corresponding lattice parameter under hydrostatic pressures, is proposed and applied to the case of CeO2 sample. The bulk modulus and its pressure derivative of fluorite phase CeO2 (K0 = 235 (18) GPa, K0′ = 3.67) are obtained by fitting the P-V results into Vinet equation of state. A discussion of the pressure dependence of α, which determines the relative weights of the isostress and isostrain conditions across the grain boundary in an actual case, is presented. [ABSTRACT FROM AUTHOR]