Temperature dependence of bismuth structures under high pressure

It is unclear whether there is a liquid-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 liquid-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 xray absorption near edge structure(XANES)spectra,we estimate the possible temperature ranges of liquid-liquid phase transition to be 779-799 K at 2.74 GPa and 859-879 K at 2.78 GPa,809-819 K at 3.38 GPa and 829-839 K at 3.39 GPa and 729-739 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(phaseⅢ-like and phase IV-like)of bismuth melts are obtained from different initial phases of bismuth solids(phaseⅢand phase IV)under the same condition(3.20 GPa and 800 K).Assuming that the bismuth melt undergoes a phase transition from IV-like toⅢ-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 liquid-liquid phase transition.

High Strain Rate Deformation Behavior of Zirconium at Elevated Temperatures

High temperature mechanical behaviors of zirconium at high strain rate of 103 s-1 were studied by split Hopkinson pressure bar （SHPB）.The influences of strain rate and temperature on the micro-structural evolution,as well as the occurrence of shear localization and subsequent fracture,were also investigated.It s found that the compressive stress-strain response depends sensitively on the applied strain rate and test temperature.Micro-structural observations revealed that the density of the twinning grains reduced as the temperature increased,and increased in response to increasing strain rate.Optical observation of the fracture surfaces showed evidence of adiabatic shear localization along the fracture planes prior to crack formation.Finally,a special form of the Zerilli-Armstrong model was used to describe the mechanical response of zirconium.