Causal relations in determining functionalities in perovskite oxides

Machine learning (ML) methods to solidify understandings on material structures and functionalities have now become common in the physical sciences community. However, the in-built correlative nature of traditional ML techniques fails to capture the causal mechanisms driving any physical phenomena. Our study focuses on exploring fundamental atomistic mechanisms behind A-site cation ordering in double perovskite oxides. The origin of cation ordering has remained as a mystery for years since several factors such as cation radii and/or oxidation states, charge ordering, cooperative first order Jahn−Teller distortions of B cations (FOJT), A-site vacancies coupled with SOJT distortion, and tilt of BO₆/B′O₆ octahedra, contribute to it. Bringing in the causal intuitions with density functional theory calculations made it possible to not only pin down the necessary condition for tunable cation ordering but also establish quantifiable (previously unknown) stricture-property relationship between geometry, modes, and ordering. A discussion on polarization switching mechanism as understood from a combination of first-principles study and causal relations will be included in the presentation.