Molecular motion and phase transition in perovskite-type (CH 3) nNH 4− nSnCl 3 ( n=1–4) studied by proton NMR spin–lattice relaxation

Abstract

Powder X-ray diffraction, 119Sn NMR spectra, and 1H NMR spin–lattice relaxation times, T 1, were measured for (CH 3) n NH 4− n SnCl 3 ( n=1–4). From the Rietveld analysis, it is shown that all four compounds crystallize into deformed perovskite-type structures at room temperature. The temperature dependence of 1H T 1 was analyzed in terms of the CH 3 reorientation and other motions of the whole cation. Except for the phase transition in CH 3NH 3SnCl 3, which is from monoclinic to rhombohedral at 331 K, 1H T 1 was continuously changed at other phase transitions in this compound as well as in the n=2–4 compounds, suggesting that the transitions are not caused by the change of the motional state of the cation but by an instability of the [SnCl 3] n n− perovskite lattice.