Atomistic insight into the defect-induced tunable plasticity and electronic properties of tetragonal zirconia

Abstract

Tetragonal zirconia (t-ZrO2) with exceptional properties is crucial in catalytic applications. Defects effectively enhance its electronic properties and plasticity, making t-ZrO2 a valuable material for high-efficiency industrial catalysts, and flexible electronic devices. In this study, we utilize first-principles calculations to compare the impact of vacancy defects and nitrogen doping on the structural and electronic properties of wide bandgap semiconductor t-ZrO2. Additionally, we analyze the tuned plasticity of t-ZrO2 by varying N-dopant and vacancy concentrations using molecular dynamics simulations and cyclic-nanoindentation tests. The estimation of energy release associated with plastic deformation is conducted using the Griffith energy balance model. Our study reveals significantly distinct electronic properties and plastic deformation maps in oxygen-deficient and N-doped t-ZrO2 compared to the perfect counterpart, where the defect nature dictates the band gap energy and plastic zone size. t-ZrO2−x exhibits a greater bandgap narrowing than t-ZrO2−xNx, resulting from increased atomic displacement, decreased free energy for plastic deformation, and enhanced plastic dissipated energy. Furthermore, we demonstrate that electronic properties and the plasticity of t-ZrO2−xNx, including bandgap energy and energy release rate during cyclic-nanoindentation, are unable to compete with those of the small-bandgap counterpart t-ZrO2−x. Herein, t-ZrO2−x, x = 0.2 exhibits the highest plasticity and the smallest bandgap of 1.28 eV, contrasting with the 5.6 eV bandgap of perfect t-ZrO2. Thereby, t-ZrO2−x displays pronounced band gap tightening and enriched flexibility, providing it a favorable semiconductor for photoelectrochemical energy conversion (PEC) applications.