Nuclear quadrupolar spin-lattice relaxation with realistic phonon density of states in alkali halides

Abstract

The nuclear quadrupolar spin-lattice relaxation times T1 have been calculated in alkali halides, whereby the phonon densities of states have been extracted from the shell model lattice dynamics. The calculations at room temperature were performed on 79Br in KBr, NaBr, and RbBr; 23Na in NaI, NaCl, and NaBr; 35Cl in NaCl and KCl; and 127I in NaI and KI. The obtained values of relaxation time T1 are an order of magnitude smaller than those calculated with the Debye-model phonon density of states and agree well with experiments. The temperature dependence of acoustic and optical phonon contributions to the nuclear relaxation rate (first-order Raman phonon process) are carried out in the temperature range 20 to 300 K for 23Na and 127I in NaI. The role of optical phonons becomes important from 77 K on; the temperature dependence of T1 agrees with experimental data throughout most of the temperature range studied (77–300 K), while differing quantitatively from the predictions obtained on the basis of the Debye model.