Rk. Subramanian et al., STRUCTURAL INSTABILITY AND ANION DYNAMICS IN THE SYSTEM (RB1-XCSX)2ZNCL4 - A CL-35 NUCLEAR-QUADRUPOLE RESONANCE STUDY, Journal of physics. Condensed matter, 6(12), 1994, pp. 2377-2384
The dynamics of the ZnCl4 anion in the paraelectric phases of (Rb]1-xC
sx)2ZnCl4 with x = 0.005, 0.01, 0.03 and 0.05 are investigated through
Cl-35 nuclear quadrupole frequency nu and spin-lattice relaxation tim
e (T1Q) studies. The data, collected as a function of temperature for
different lines in these compounds, are analysed to obtain the hinderi
ng potential barrier heights and the relative mean square amplitudes f
or librational motions parallel and perpendicular to the a-axis of the
crystal structure. A comparison of these results shows that the prese
nce of impurity affects only perpendicular motions and the correspondi
ng potential becomes anharmonic, probably developing a double-well str
ucture, as the concentration of impurity increases. As the paraelectri
c-incommensurate transition temperature is suppressed by the presence
of impurity, the above results suggest that the perpendicular motions
have an important role to play in stabilizing the paraelectric phase i
n this system.