Structural and electronic phase transitions in Zr$_{1.03}$Se$_{2}$ at high pressure

TL;DR

This study investigates high-pressure structural and electronic phase transitions in Zr$_{1.03}$Se$_{2}$, revealing a gradual transition from hexagonal to monoclinic phases and a pressure-induced metal-semiconductor transition influenced by excess Zr.

Contribution

It provides detailed insights into the structural and electronic phase transitions of Zr$_{1.03}$Se$_{2}$ under high pressure, highlighting the effects of excess Zr and identifying a Kondo effect.

Findings

Structural transition from hexagonal to monoclinic phase with mixed phases between 5.9 and 14.8 GPa.

Electronic transition from metallic to semiconducting behavior above 7.3 GPa.

Presence of Kondo effect attributed to excess Zr in the sample.

Abstract

A detailed high pressure investigation is carried out using x-ray diffraction, Raman spectroscopy and low temperature resistivity measurements on hexagonal ZrSe$_{2}$ having an excess of 3 at.\% Zr. Structural studies show that the sample goes through a gradual structural transition from hexagonal to monoclinic phase, with a mixed phase in the pressure range 5.9 GPa to 14.8 GPa. Presence of a minimum in the $c/a$ ratio in the hexagonal phase and a minimum in the full width half maximum of the $A_{1g}$ mode at about the same pressure indicates an electronic phase transition. The sample shows a metallic characteristic in its low temperature resistivity data at ambient pressure, which persist till about 5.1 GPa and can be related the presence of slight excess Zr. At and above 7.3 GPa, the sample shows a metal to semiconductor transition with the opening of a very small band gap, which increases with pressure. The low temperature resistivity data show an upturn, which flattens with an increase in pressure. The phenomenological analysis of the low temperature resistivity data indicates the presence of Kondo effect in the sample, which may be due to the excess Zr.