ORDER-DISORDER PHASE-TRANSITION AND DIMETHYL AMMONIUM GROUP-DYNAMICS IN [(CH3)2NH2]3SB2CL9- PROTON NMR-STUDY

Cation dynamics in tris(dimethylammonium) nonachloro-diantimonate, whi ch exhibits paraelectric-ferroelectric phase transition, is studied th rough proton spin lattice relaxation and second moment studies. Result s show a clear signature of this phase transition. Analysis of the dat a based on a recent model indicates a freezing of isotropic motion of the dimethylammoiun (DMA) cation at the phase transition, as well as t he existence of dynamically inequivalent DMA and methyl groups, both i n the ratio of 1:1 in the low temperature phase. Activation energies a ssociated with the dynamics of different inequivalent cations and meth yl groups are calculated. These results are compared with similar stud ies on related compounds comprising of tetramethyl and trimethyl ammon ium groups.