Phase Transition and Cation Dynamics in (CH_3ND_3)Bi_2Cl_11 Crystal as Studied by ^1H and ^2H NMR

Abstract

The temperature dependence of the ¹H NMR spin-latticerelaxation time (T₁) and ²H spectra were measured in(CH₃NH₃)₅Bi₂Cl₁₁ and (CH₃ND₃)₅Bi₂Cl₁₁ toinvestigate dynamic nature of the paraelectric-ferroelectric phasetransition. T₁ anomaly was observed in the close vicinity of thetransition temperature of 306.5, K and attributed to criticalfluctuation associated with the phase transition. The precessionalmotion of the methylammonium cation derived from the observed ²Hspectra seems to be concerned with the order-disorder transitionexpected from the X-ray study.