Empirical equations to estimate tetragonal to cubic phase transitions in lead iodide perovskites

Phase transitions in halide perovskites are well-studied due to their fundamental and applied importance. A wide range of different symmetries may appear depending on the composition, temperature, etc. For lead iodide perovskites, fortunately, the transition near room temperature is almost always between tetragonal and cubic phases. Knowing these transitions and the stable phase under a given condition can have technological implications. Although extensively studied, the current literature lacks simple tools to estimate these transition temperatures. To address this, we meticulously collected literature and compiled a database containing phase information for a wide range of APbI₃-type compositions. Data from single-phase systems were converted into easily obtainable physicochemical descriptors, and regression tools were applied, namely multivariate linear analysis and the recent method known as SISSO (sure independence screening and sparsifying operator). Simple empirical equations were determined and applied to specific systems, and their limitations and potentialities are discussed. This work advances the understanding of the topic and provides additional insights of interest for future developments in the field.