Phase transition, superstructure and physical properties of K2Fe4Se5

TL;DR

This study investigates the structural features, phase transitions, and physical properties of K2Fe4Se5, revealing a superstructure due to Fe-vacancy order, semiconducting behavior, and a transition to disorder at high temperature.

Contribution

It provides detailed structural and thermal analysis of K2Fe4Se5, highlighting Fe-vacancy ordering and its transition, which advances understanding of its phase behavior and relation to superconductivity.

Findings

Fe-vacancy order forms a superstructure in K2Fe4Se5.

K0.8Fe1.6Se2 transitions from ordered to disordered Fe-vacancy structure at 600K.

Resistivity measurements show semiconducting behavior.

Abstract

The structural features and physical properties of the antiferromagnetic K0.8Fe1.6Se2 (so called K2Fe4Se5 phase) have been studied in the temperature range from 300K up to 600K. Resistivity measurements on both single crystal and polycrystalline samples reveal a semiconducting behavior. Structural investigations of K2Fe4Se5 by means of transmission electron microscopy and powder x-ray diffraction demonstrate the presence of a well-defined superstructure within the a-b plane originating from a Fe-vacancy order along the [130] direction. Moreover, in-situ heating structural analysis shows that K0.8Fe1.6Se2 undergoes a transition of the Fe-vacancy order to disorder at about 600K. The phase separation and the Fe-vacancy ordering in the superconducting materials of KxFe2-ySe2 (0.2 \leq y \leq 0.3) has been briefly discussed.