High-Pressure Structural Phase Transitions in FeAs Based Compounds at Ambient and Low Temperatures

摘要

We report high pressure powder x-ray diffractions studies for AFe_(2)As_(2) (A(velence)Ba and Ca) at high pressures up to 56 GPa at 300 K and low temperatures down to 33 K. A phase transition to a collapsed tetragonal phase is observed in AFe_(2)As_(2). However, at 300 (33) K in Ba-compound the transition occurs at 26 (29) GPa, which is much higher pressure than 1.7 (0.3) GPa at 300 (40) K in the Ca-compound, due to its larger volume. The transition to collapsed phase occurs in the two compounds at nearly the same values of unit cell volume and c_(t)/a_(t) ratio. We present a detailed analysis of the pressure dependence structure phase transitions and equation of state in these important FeAs compounds.