127I-NQR, 119 Sn Mössbauer Effect, and Electrical Conductivity of MSnI3 (M = K, NH4 , Rb, Cs, and CH3NH3 )

Abstract

In a series of MSnI₃ compounds (M = K, NH₄ , Rb, Cs, CH₃NH₃) two types of coordination around the central Sn(II) were found by ¹²⁷I-NQR and powder X-ray diffraction techniques. They are square pyramidal (for M = NH₄ , Rb) and octahedral (for M = CH₃NH₃). CsSnI₃ , on the other hand, showed a drastic structural change of the anion at 425 K from a square pyramid to a regular octahedron. Associated with this phase transition, the electrical conductivity increased from 4 x 10^-3 S cm^-1 to about 10² S cm^-1 . This metallic modification was characterized by ¹²⁷I-NQR and ¹¹⁹Sn Mössbauer spectroscopy.