New insight into the intrinsic instability of fcc ZrH2 by energy-resolved local bonding analysis

Abstract

The electronic-driven instability of fcc ZrH₂ due to the reduction of density of states (DOS) at E_F under the tetragonal distortion were used to be explained by Jahn–Teller effect or the shift of von Hove singularity. Here we explain this intrinsic instability with energy-resolved local bonding analysis by means of first-principles calculations. Our local bonding analysis reveals that this intrinsic instability stems from the peak of T_2g and E_g orbitals at E_F with the former contributing much more. Tetragonal distortion lifts the T_2g and E_g degenerate orbitals, causing the change to local Zr–H and Zr–Zr bonding. These two fct structures share similar Zr–H bonding but different Zr–Zr bonding due to the different Zr–Zr distances. For all these three structures, Zr-4s and 4p electrons do not contribute to any bonding but partially Zr-5s electrons participate in the Zr–H bonding. We discuss the hybridization of Zr and H orbitals for these three ZrH₂ structures. Presented calculations support the Jahn–Teller type effect and provide a comprehensive understanding of the intrinsic instability of Zr dihydrides.