NMR study of cation motion in guanidinium iodoplumbates

Abstract

Proton NMR second moments and spin-lattice relaxation times of polycrystalline C(NH2)3PbI3 and [C(NH2)3]2PbI4 were studied in a wide temperature range. The order-disorder character of the existing solid-solid phase transitions was confirmed and for tetraiodoplumbate a new phase transition at 170 K was discovered. For both compounds a dynamical inequivalence and unusual high mobility of the guanidinium cations were revealed. For the reorientations discovered (NH2 group flipping, C3 in-plane reorientation and a tumbling) the activation parameters were determined.