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Compressibility and pressure-induced disorder in superconducting phase-separated Cs0.72Fe1.57Se2

Pressure-dependent diffraction response of the superconducting phase separated Cs0.72Fe1.57Se2 has been studied using synchrotron radiation up to the pressure of 19 GPa. The main and secondary phases of Cs0.72Fe1.57Se2 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 least 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 slower at room temperature. Together with the previously reported pressure-dependent resistivity and magnetic susceptibility measurements, this work indicates that superconductivity in the AxFe2-ySe2 (A - alkali metals) phases could be related to the Fe-vacancy ordering in the main phase.