Postcotunnite phase of the intermetallic compound AuIn2at high pressure

We report a structural phase transition in AuIn2 above 25 GPa. The inferred structure of this phase is post cotunnite (P112(1)/a). Combining the new results with previously observed behavior of AuIn2, we propose a sequence of structural transitions from CaF2 (Fm3m) to amorphous phase at 24 GPa to monoclinic (P112(1)/a) structure at 25.6 GPa. During decompression the high-pressure phase is preserved to the pressure of 9.4 GPa and it finally transforms back to the Fm3m phase. Analysis of volume reduction and bulk modulus increase reveals close similarity with the postcotunnite phase observed in PbCl2. This study is important in understanding the behavior of metallic phases of various oxides of geophysical interest which exist in CaF2 fluorite-type structure.