Resolving the pressure induced 'self-insertion' in skutterudite CoSb3

TL;DR

This study investigates the structural stability and phase transformations of CoSb3 under high pressure, revealing a 'self-insertion' transition, effects of different pressure media, and a new phase transition above 40 GPa.

Contribution

It provides detailed insights into pressure-induced structural changes and phase behavior of CoSb3, including the discovery of a new phase transition and effects of nonhydrostatic stresses.

Findings

Self-insertion transition can reduce or reverse compressibility.

Discovered a new phase transition from cubic to trigonal above 40 GPa.

Pressure transmitting media influence the structural stability and transition behavior.

Abstract

CoSb3, a skutterudite compound, is key in studying thermoelectric materials. Under compression, it undergoes a 'self-insertion' isostructural transition, redistributing large Sb atoms among crystallographic sites. We investigated CoSb3's structural stability up to 70 GPa using single crystal X-ray diffraction and high-resolution X-ray scattering, including Bragg Coherent Diffraction Imaging. We examined the material in three pressure transmitting media (PTMs), exploring how PTMs and nonhydrostatic stresses affect CoSb3. Notably, the 'self-insertion' transition may reduce or even make compressibility negative. Additionally, we report a previously unknown phase transformation from cubic Im-3 to trigonal R-3 above 40 GPa and discuss the phases' distinctive behaviors.