Phase Transition and Electric Conductivity of ASnCl3 (A = Cs and CH3NH3)

Abstract

A first-order phase transition of CsSnCl3 to a cubic perovskite phase was observed at Ttr = 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 119Sn NMR 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 119Sn NMR T1. The electric conductivity of Cs and CH3NH3 salts, however, is governed by the semiconducting property of these compounds.