Pressure-driven phase transitions in bulk HfS$_2$

TL;DR

This study investigates how hydrostatic pressure affects the Raman spectra of bulk HfS$_2$, revealing two pressure-induced structural transformations with distinct spectral signatures and potential permanent changes.

Contribution

The paper reports the discovery of two pressure-driven phase transitions in bulk HfS$_2$ and characterizes their spectral signatures and potential structural implications.

Findings

Two distinct pressure-induced transformations observed between 5.7-9.8 GPa and 12.8-15.2 GPa.

Post-transformation spectra show increased vibrational modes and altered lineshape.

High-pressure phase appears to be disordered and permanently retained after decompression.

Abstract

The effect of hydrostatic pressure up to 27 GPa on the Raman scattering (RS) in bulk HfS$_2$ is investigated. There are two transformations of RS spectra, which take place during compression at pressure between 5.7 GPa and 9.8 GPa as well as between 12.8 GPa and 15.2 GPa. Seven vibrational modes can be observed after the transformation, as compared to four modes before the transformation. The observed change suggests structural change in the material of yet unknown nature. The frequencies of the RS modes observed above the transformation change linearly with pressure and corresponding pressure coefficients have been determined. The other transition manifests itself as a change in the RS lineshape. While a series of well-defined RS modes are observed under pressure below the transition, broad spectral bands can be seen at higher pressure. The overall lineshape of the spectra resembles that of disordered materials. The lineshape does not change during decompression, which suggests permanent nature of the high-pressure transition.