Comparative structural evolution under pressure of powder and single crystals of the layered antiferromagnet FePS$_3$

TL;DR

This study investigates the high-pressure structural changes of FePS$_3$, revealing a symmetry increase and inter-planar collapse, with findings sensitive to experimental conditions like pressure medium.

Contribution

It provides definitive evidence for the high-pressure structure of FePS$_3$, clarifying previous conflicting models through combined single-crystal and powder diffraction analysis.

Findings

High-pressure transition involves inter-planar collapse and symmetry increase.

Volume collapse is influenced by the pressure medium used.

The structural transition is linked to an insulator-metal transition.

Abstract

The layered antiferromagnet FePS$_3$ has been shown to undergo a structural transition under pressure linked to an insulator-metal transition, with two incompatible models previously proposed for the highest-pressure structure. We present a study of the high-pressure crystal structures of FePS$_3$ using both single-crystal and powder x-ray diffraction. We show that the highest pressure transition involves a collapse of the inter-planar spacing of this material, along with an increase in symmetry from a monoclinic to a trigonal structure, to the exclusion of other models. The extent of this volume collapse is shown to be sensitive to the presence of a helium pressure medium in the sample environment, indicating that consideration of such experimental factors is important for understanding high-pressure behaviours in this material.