Defect interaction and local structural distortions in Mg-doped LaGaO₃: A combined experimental and theoretical study

A combined experimental and theoretical study of Mg-doped LaGaO₃ electrolyte was carried out, with the aim to unveil the interaction between oxygen vacancy (Vo) and perovskite B site cations. LaGaO₃ (LG) and LaGa_0.875Mg_0.125O_2.938 (LGM0125) samples were comprehensively characterized by X-ray absorption spectroscopy (XAS) and X-ray diffraction, in order to investigate short- and long-range structures of both undoped and Mg-doped materials. XAS analysis evidenced a preferential Ga-Vo interaction in LGM0125, confirmed by periodic hybrid density functional theory calculations, which were combined with a symmetry-independent classes (SICs) approach in order to (a) obtain a detailed picture of the different Mg and Vo configurations in the doped material and (b) characterize the structural features of the conducting sites. Among the 28 structures of LGM0125 considered in the SIC approach, the Ga-Vo-Ga and Ga-Vo-Mg axial configurations (oriented along the b crystallographic axis) were found to be the most stable. The relative stability of all vacancy configurations considered could be related to geometric distortions of the B-sites, possibly significantly affecting the oxygen-ion diffusion process in such electrolytes.