Abstract
A single-phase high-pressure (HP) modification of 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 -type structure without ordering of the Fe vacancies within the Fe-deficient layers. The HP polymorph is found to be less crystalline and nearly twice as soft compared to the parent major and minor phases of . It can be quenched to low pressures and is stable at least on the scale of weeks. At ambient pressure the HP polymorph of is expected to exhibit different superconducting properties compared to its LP minor phase ().
- Received 6 December 2017
- Revised 10 April 2018
DOI:https://doi.org/10.1103/PhysRevB.97.214512
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