Structural effects on oxygen vacancies and redox behavior in Mn-based perovskite oxides
Vika Arzumanyan, Cijie Liu, Dawei Zhang, Wei Li, Jian Luo, Xingbo Liu, Yue Qi
Abstract
A series of perovskite oxides Ln 2 / 3 A 1 / 3 Mn O 3 (Ln = La, Pr, Nd, Gd; A = Ba, Sr) was investigated to understand the effects of A-site cation size on oxygen vacancy formation. Quasirandom L n 2 / 3 A 1 / 3 Mn O 3 mixed structures were generated using Alloy Theoretic Automated Toolkit (ATAT), followed by density functional theory (DFT) calculations. While mixing the orthorhombic LnMn O 3 structures with the hexagonal AMnO 3 structures leads to lattices and global symmetries closer to cubic, the average volume generally increases with the average ionic size, and the local bond and angles exhibit more variations due to A-site mixing. DFT calculations and a statistical model were combined to predict oxygen reduction abilities. Thermogravimetric analysis (TGA) provided experimental validation of these predictions by measuring changes in oxygen non-stoichiometry ( Δδ ) under controlled conditions. Both indicated that larger A-site ionic size differences lead to greater Δδ , consistent with the larger variation in local structures, and enhanced redox capabilities. This combined computational-experimental approach highlights the importance of local structure variation, instead of average properties, in A-site cation engineering to optimize perovskite oxides for different devices relying on oxygen vacancy redox activity. • A-site cation mixing increases distortions and shifts global symmetry toward cubic. • DFT and statistics predict oxygen reduction behavior of mixed compositions. • TGA confirms Δδ increases with A-site size mismatch and structural variation. • Local distortions, not averages, control oxygen vacancy redox performance.