Phase transition and superconductivity of SrFe₂As₂ under high pressure

High pressure x-ray diffraction and electrical resistance measurements have been carried out on SrFe₂As₂ to a pressure of 23GPa and temperature of 10K using a synchrotron source and designer diamond anvils. At ambient temperature, a phase transition from the tetragonal phase to a collapsed tetragonal (CT) phase is observed at 10GPa under non-hydrostatic conditions. The experimental relation that T-CT transition pressure for 122 Fe-based superconductors is dependent on ambient pressure volume is affirmed. The superconducting transition temperature is observed at 32K at 1.3 GPa and decreases rapidly with a further increase of pressure in the region where the T-CT transition occurs. Our results suggest that T_C falls below 10K in the pressure range of 10-18GPa where the CT phase is expected to be stable.