Deuteron NMR and a Model for Phase Transitions in Monoclinic RbD 2 PO 4 .

Abstract

The quadrupole-perturbed deuteron NMR spectra and spin-lattice relaxation times of monoclinic RbD2PO4 have been measured and the electric-field-gradient tensors at the deuteron sites have been determined in phase I at 110 °C, phase III at 80 °C, and phase III at 40 °C. The results are incompatible with a location of the D(2) and D(3) deuterons in the center of the corresponding H bonds. They show that these deuterons are disordered between two off-center sites in phases I and II, whereas they are ordered in phases III and IV. A four-sublattice model accounting for all four phase transitions in monoclinic RbD2PO4 is proposed.