Thermodynamic Study of Formamidinium Lead Iodide (CH 5 N 2 PbI 3 ) from 5 to 357 K.

In the present study, the molar heat capacity of solid formamidinium lead iodide (CH 5 N 2 PbI 3 ) was measured over the temperature range from 5 to 357 K using a precise automated adiabatic calorimeter. In the above temperature interval, three distinct phase transitions were found in ranges from 49 to 56 K, from 110 to 178 K, and from 264 to 277 K. The standard thermodynamic functions of the studied perovskite, namely the heat capacity C ° p ( T ), enthalpy [ H 0 ( T ) - H 0 (0)], entropy S 0 ( T ), and [ G °( T ) - H °(0)]/ T , were calculated for the temperature range from 0 to 345 K based on the experimental data. Herein, the results are discussed and compared with those available in the literature as measured by nonclassical methods.