Phase transition and electric conductivity of ASnCl3 (A = Cs and CH3NH3)

A first-order phase transition of CsSnCl3 to a cubic perovskite phase was observed at T-tr = 379 K. The electric conductivity increased from 10(-6) S cm(-1) to 10(-3) S cm(-1) at the phase transition. The temperature dependence of the electric conductivity and the X-ray diffraction data for CsSnCl3 suggested a reconstructive nature of the phase transition. On the other hand, CH3NH3SnCl3 showed successive phase transitions at 283, 307, 331, and 463 K with increasing temperature. The highest temperature phase belongs to a cubic perovskite structure, and pyramidal SnCl3- anion exists below 465 K having distorted perovskite structures. The (SnNMR)-Sn-119 spectra for CH3NH3SnCl3 supported the coordination change around the Sn atom, and also suggested the onset of chloride-ion diffusion just below the phase-transition temperature to the cubic phase. The activation energy for chloride-ion diffusion was found to be 54 kJ mol(-1) by analyzing the temperature dependence of Sn-119 NMR T-1. The electric conductivity of Cs and CH3NH3 salts, however, is governed by the semiconducting property of these compounds.