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

Cation dynamics in tris(dimethylammonium) nonachloro-diantimonate, which exhibits paraelectric-ferroelectric phase transition, is studied through proton spin lattice relaxation and second moment studies. Results show a clear signature of this phase transition. Analysis of the data based on a recent model indicates a freezing of isotropic motion of the dimethylammoiun (DMA) cation at the phase transition, as well as the existence of dynamically inequivalent DMA and methyl groups, both in the ratio of 1:1 in the low temperature phase. Activation energies associated with the dynamics of different inequivalent cations and methyl groups are calculated. These results are compared with similar studies on related compounds comprising of tetramethyl and trimethyl ammonium groups.