²³Na quadrupolar and dielectric relaxation study on dynamics and metastability in (K-Na)TaO₃

23 Na quadrupolar spin-lattice relaxation and dielectric dispersion data are reported for mixed crystals (K-Na)TaO 3 . Below 150K, the Na ions are shown to associate a dipole moment of 0.04 AA e - , which changes orientations among equivalent (100) directions. This hopping motion contributes to both dielectric and spin-lattice quadrupolar relaxation, thus allowing evaluation of the dipole reorientation rates. These appear to be widely distributed and, in particular at low temperature, their low-frequency tail is likely to prevent the thermodynamical equilibrium state being reached in experimental times. Some dynamics of resonant character is observed at 4K.