A comparative study of the physical properties of layered transition metal nitride halides MNCl (M = Zr, Hf): DFT based insights

TL;DR

This study uses DFT calculations to compare the mechanical, optical, and electronic properties of layered transition metal nitride halides ZrNCl and HfNCl, revealing differences in their anisotropy, band gaps, and potential applications.

Contribution

It provides a detailed first-principles comparison of ZrNCl and HfNCl's properties, highlighting their differences and potential uses in semiconducting and optical applications.

Findings

HfNCl is more machinable and softer than ZrNCl.

ZrNCl exhibits stronger layering and is more brittle.

HfNCl has a larger band gap and better ultraviolet absorption.

Abstract

ZrNCl and HfNCl belong to a class of layered transition metal nitride halides MNCl (M= Zr,H). They are from the space group R-3m (No-166) and crystallize in the rhombohedral structure. Both of these materials have shown promising semiconducting behaviors. Recent studies have shown their versatility as semiconductors and also as superconductors when intercalated with alkaline metals. This paper explores the mechanical, optical and electronic properties of these two semiconducting crystals in depth. A comparative study between the two materials in their elastic constants, anisotropy measures, electronic density of states and band structures, optical spectra has been performed with first principles density functional theory (DFT) based calculations within the local density approximation (with appropriate U for the energy gap calculations in case of HfNCl). HfNCl is more machinable than ZrNCl and is relatively softer as indicated by the lower Debye temperature. ZrNCl has stronger layering due to which it exhibits brittle nature. HfNCl has a larger band gap. ZrNCl is a better reflector of ultraviolet radiation. On the other hand HfNCl is a good ultraviolet absorber. Both materials are anisotropic in regards to structure, electronic energy dispersion and optical parameters. Overall, the degree of anisotropy is more prominent in ZrNCl compared to that in HfNCl. Possible sectors for applications of ZrNCl and HfNCl semiconductors are discussed.