Enhanced phase transition temperature achieved by CH3/H substitution in Sn-based perovskite

Organic-inorganic hybrid phase transition materials have garnered significant attention due to their excellent properties and broad applications in energy storage, temperature control switches, and optoelectronic devices. The regulation of the phase transition temperature (T_c) is necessary as it determines the properties and applications of materials. (TMTBA)₂SnBr₆ (1) (TMTBA = N,N,N-trimethyl‑tert-butylammonium) was synthesized, featuring the T_c around 225 K and then (DMTBA)₂SnBr₆ (2) (DMTBA = N,N-dimethyl‑tert-butylaminium) was obtained. Progressively, the 2 exhibited a great enhancement of T_c at 404 K, with a ΔT_c reaching up to 179 K. Single-crystal structure analysis confirmed that 1 underwent isomorphic phase transitions, with the space groups of Pnma. In contrast, 2 underwent an order-disorder phase transition, and the space group changed from the low-temperature phase of I2/c to high-temperature phase of $R\overline{3}$. What's more, the semiconductor properties and optical band gap of the materials were also investigated, 2.59 eV for 1 and 2.65 eV for 2. It is believed that this work can enrich the field of phase transition materials and provide some guidance for the regulation of T_c.