Kinetic Scaling Rules Governing Phase Instability in Perovskite Halides

Perovskite halides (ABX₃) offer remarkable promise for next-generation electronic and optoelectronic technologies, yet their deployment is fundamentally limited by intrinsic thermal phase instability. Despite extensive study, the mechanisms governing decomposition and structural transitions remain unresolved, partly because prevailing stability metrics emphasize thermodynamics while overlooking the coupled ion-migration kinetics that dominate degradation. Here, we identify two universal linear scaling relationships that quantitatively link macroscopic instability temperatures to microscopic ion-migration kinetics. Using first-principles calculations combined with experimental validations across diverse single and double perovskite chemistries, we show that the decomposition temperature of cubic perovskite halides increases linearly with the composite serial "resistance" of A-X and B-X migration barriers, capturing the coupled kinetic difficulty of bond rupture required for lattice breakdown. In contrast, the cubic-to-tetragonal transition temperature scales with a distinct kinetic descriptor: the differential shift in cation and anion migration barriers projected along the crystallographic c-axis, which governs the ease of symmetry-breaking distortions. Together, these relationships enable accurate prediction of instability temperatures across a broad chemical space and reconcile previously disparate observations of perovskite stability. By revealing composite ion-migration kinetics as the dominant unifying driver of phase instability, this work provides a general design principle for engineering intrinsically stable halide perovskites and overcoming a central bottleneck in their technological maturation.