DEUTERON NMR-STUDY OF DYNAMICS AND OF COEXISTENCE OF PARAELECTRIC ANDFERROELECTRIC PHASES IN RB0.90(ND4)0.10D2ASO4

The deuteron glass Rb1-x(ND4)xD2AsO4 (DRADA) is a mixed crystal of RbD 2AsO4 (DRDA) and ND4D2AsO4 (DADA). Deuteron nuclear magnetic resonance has been performed on the acid and ammonium deuterons. The crystal st udied has an ammonium concentration (x = 0.10) that puts it in the coe xistence region of the phase diagram. Line-shape measurements of the a mmonium deuterons show the coexistence of the ferroelectric (FE) and p araelectric (PE) phases as the temperature is lowered below the ferroe lectric-phase-transition temperature T(c). The acid deuteron line shap e on the other hand is found to broaden as the temperature is reduced but is unaffected by the ferroelectric transition. Spin-lattice-relaxa tion measurements have been performed and the activation energies for the relaxation processes have been computed. The relaxation-rate anoma ly for acid deuterons in the ferroelectric-transition range indicates a short correlation length for the FE phase in the coexistence region of the phase diagram.