Elementary Excitations in Order-Disorder Systems Studied by NQR*

NQR and NMR methods allow for the investigation of incommensurately modulated structure because the resonance frequencies change in space in such a way that they reflect the variation of the incommensurate (I) modulation. Much work has been carried out on the steady state of these systems, but dynamical studies are limited [1, 2]. The NQR spinlattice relaxation time Tj has been studied by us and other groups [3-5] in Rb2ZnCl4 at the CI anion position. For the homogeneous linewidth (spin-spin relaxation time T2), the only information available concerns pure crystals of the A2BX4 family [6-8]. In continuation of our previous investigation on the elementary excitations of these systems we decided to study [Rb1_JC(NH4)x]2ZnCl4 , where (NH4) acts as an impurity (x = 0.00, x = 0.01, x = 0.04), as a function of temperature.