Formation of single-phase disordered CsxFe2-ySe2 at high pressure

TL;DR

This study reports the synthesis of a single-phase high-pressure form of CsxFe2-ySe2 at 11.8 GPa, which is structurally similar to a low-pressure superconducting phase but exhibits different physical properties.

Contribution

It introduces a new high-pressure polymorph of CsxFe2-ySe2 with distinct structural and mechanical properties, stable at ambient conditions.

Findings

High-pressure CsxFe2-ySe2 is less crystalline and softer.

It can be quenched and remains stable at low pressures.

Expected different superconducting properties at ambient pressure.

Abstract

A single-phase high pressure (HP) modification of CsxFe2-ySe2 was synthesized at 11.8 GPa at ambient temperature. Structurally this polymorph is similar to the minor low pressure (LP) superconducting phase, namely they both crystallize in a ThCr2Si2-type structure without ordering of the Fe vacancies within the Fe-deficient FeSe4 layers. The HP CsxFe2-ySe2 polymorph is found to be less crystalline and nearly twice as soft compared to the parent major and minor phases of CsxFe2-ySe2. It can be quenched to low pressures and is stable at least on the scale of weeks. At ambient pressure the HP polymorph of CsxFe2-ySe2 is expected to exhibit different superconducting properties compared to its LP minor phase (Tc = 27 K).