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

Abstract

We report high pressure powder x‐ray diffractions studies for AFe2As2 (A = 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 AFe2As2. 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 ct/at ratio. We present a detailed analysis of the pressure dependence structure phase transitions and equation of state in these important FeAs compounds.