CL-35 NUCLEAR-QUADRUPOLE RESONANCE STUDY OF ANION DYNAMICS IN THE PARAELECTRIC PHASES OF CS2ZNCL4 AND RB2ZNCL4

The dynamics of the ZnCl4 anion in two compounds, one exhibiting a str uctural transition to an incomensurate phase (Rb2ZnCl4) and another no t having any structural transition at all (Cs2ZnCl4), are studied thro ugh Cl-35 NQR frequency (nu) and relaxation time (T1Q) measurements as a function of temperature T in their high-temperature (paraelectric) phases. Estimates of the potential barriers hindering the reorientatio nal motions of ZnCl4 anions along axes parallel and perpendicular to t he a axis of the crystal structure are obtained from the T1Q data. The se results are analysed in conjunction with a qualitative comparison o f relative mean square amplitudes of such motions obtainable from freq uency data, in order to investigate the differences in the dynamics an d structure of the ZnCl4 anion. There seems to be correlation between the dynamics of the anion in this phase and the possibility that the c ompound may exhibit a structural instability at low temperatures in th is family.