The pressure-dependent diffraction response of the superconducting phase-separated ${\mathrm{Cs}}_{0.72}$${\mathrm{Fe}}_{1.57}$${\mathrm{Se}}_2$ ($T_{\mathrm{c}}$ = 28.5 K) has been studied at room temperature using synchrotron radiation up to the pressure of 19 GPa. The main and secondary phases of ${\mathrm{Cs}}_{0.72}$${\mathrm{Fe}}_{1.57}$${\mathrm{Se}}_2$ have been observed in the whole pressure range. The main ordered phase has been found to undergo an order-disorder transition in the Fe sublattice at $P$ = 11 GPa with the corresponding kinetics on the order of hours. Contrary to the analogous temperature-induced transition, the secondary phase has not been suppressed suggesting that its stability pressure range is higher than 19 GPa or the corresponding transformation kinetics is too slow at room temperature. Together with the previously reported pressure-dependent resistivity and magnetic susceptibility measurements, this work indicates that superconductivity in the $A_x$${\mathrm{Fe}}_{2-y}$${\mathrm{Se}}_2$ ($A$: alkali metals) phases could be related to the Fe-vacancy ordering in the main phase.

• Received 28 February 2014
• Revised 27 March 2014

DOI:https://doi.org/10.1103/PhysRevB.89.144106