A systematic ab initio study of vacancy formation energy, diffusivity, and ionic conductivity of Ln2NiO4+δ (Ln=La, Nd, Pr)

Abstract

This study systematically investigates the vacancy formation energy, diffusivity, and ionic conductivity of the Ln2NiO4+δ (Ln = La, Nd, Pr, and δ = 0.125) compound using the ab initio approach. Specifically, the impact of thermal expansion on the oxygen transport properties is considered, using a combination of quasi-harmonic approximation (QHA) and a linear regression model to study and reproduce the temperature-dependent properties of Ln2NiO4+δ. Overall, the predictions are in excellent agreement with previous theoretical studies in the literature. It is confirmed that the ionic transport properties of the Ln2NiO4+δ are not dominated by oxygen vacancy diffusion due to the high vacancy formation energy. Additionally, the interstitialcy mechanism, which involves interstitial O2- hopping parallel to the a-b plane with the rocksalt layer, is determined to be the more favorable diffusion path. Meanwhile, the predicted energy barrier, diffusion coefficient, and ionic conductivity of Ln2NiO4+δ show reasonable agreement with experimental data, with Pr2NiO4+δ exhibiting the lowest activation energy barrier (ΔEb = 0.722 eV) and the highest thermal expansion, diffusivity, and ionic conductivity. Overall, this study presents an efficient and computationally facile tool for predicting ionic transport properties in materials where thermal expansion is the main driving force for temperature-dependent properties.