Phenomenological correlations and heat capacity scaling in lead halide perovskites at low temperatures

The study of heat capacity in various lead halide perovskites within temperature range of 1.8–25 K has revealed universal amorphous-like features. Regardless of dimensionality, cation type or halide, all perovskites exhibited a boson peak, shifting between 5 and 9 K. Although no direct correlations were identified between specific approximation parameters and perovskite characteristics based on raw heat capacity data, a universal behavior emerged when the disorder-related contribution was subtracted and the data were approximated using a normalized dimensionless function Δ*. This approach confirmed the universality of excess heat capacity in C_p/T³ vs T. Furthermore, the validity of the Granato correlation was demonstrated, with the ratio between Debye temperature and boson peak temperature consistently falling within 20–28, suggesting the emergence of a new material classification. The successful heat capacity scaling and phenomenological correlation reinforce the universal nature of excess heat capacity at low temperatures, indicating that the proposed dimensionless function is applicable not only to crystalline and glassy materials but also to perovskites exhibiting glass-like characteristics.