Prediction of semi-metallic tetragonal Hf2O3 and Zr2O3 from first-principles

TL;DR

This study predicts semi-metallic tetragonal phases of Hf2O3 and Zr2O3 using first-principles calculations, revealing their stability and potential relevance to resistive memory devices.

Contribution

It introduces the stable tetragonal structures of Hf2O3 and Zr2O3 derived from density functional theory, highlighting their semi-metallic nature and possible application in RRAM.

Findings

Tetragonal Hf2O3 and Zr2O3 are more stable than their corundum forms.

Both phases are semi-metallic with high carrier concentrations.

The tetragonal Hf2O3 phase may relate to low resistivity states in RRAM.

Abstract

A tetragonal phase is predicted for Hf2O3 and Zr2O3 using density functional theory. Starting from atomic and unit cell relaxations of substoichiometric monoclinic HfO2 and ZrO2, such tetragonal structures are only reached at zero temperature by introducing the oxygen vacancy pair with the lowest formation energy. The tetragonal Hf2O3 and Zr2O3 structures belong to space group P-4m2 and are more stable than their corundum structure counterparts. These phases are semi-metallic, as confirmed through further G0W0 calculations. The carrier concentrations are estimated to be 1.77E21 cm^{-3} for both electrons and holes in tetragonal Hf2O3, and 1.75E21 cm^{-3} for both electrons and holes in tetragonal Zr2O3. The tetragonal Hf2O3 phase is probably related to the low resistivity state of hafnia-based resistive random access memory (RRAM).