PRESSURE-DEPENDENCE OF IODINE NUCLEAR-RELAXATION IN RUBIDIUM IODIDE

The pressure-induced polymorphic phase transition at about 4 kbar in rubidium iodide was studied using nuclear magnetic resonance. The signature of the structural transition is a loss of echo intensity which presumably is due to an increase in the number of lattice defects as result of the transition. The ratio of the spin-spin relaxation times of the iodine nuclei in the two phases is in agreement with the ratio predicted by a second moment calculation. The actual experimental values, however, are considerably smaller than the theoretical predictions signifying the migration of lattice defects. Estimates of the iodine spin-lattice relaxation time at atmospheric pressure indicate the necessity to include both an anharmonic Raman contribution and a covalency factor. The change in spin-lattice relaxation time with pressure as measured in the low pressure phase is dominated by the change in the lattice parameter. The pressure derivative of the spin-lattice relaxation time in the high pressure phase is nearly equal to that in the low pressure phase.