NMR Investigation of the Quadrupolar Glass Na(CN)xCli_x

The freezing process o f the CN dumbbells in the orientational glass N a(C N )YCl!_x was studied by 23Na and 35C1 NM R for several concentrations x. The systems with x ^ 0.7 undergo structural phase transitions, whereas systems with x ;$ 0.7 stay cubic on the average down to lowest temperatures. For concentrations x % 0.65, the temperature dependences o f the NM R line widths give evidence that the transition into the glass state essentially consists in a deformation o f the local potential leading to a formation o f preferential directions for the orientations o f the CN ions. The temperature dependence of the spin lattice relaxation time T, shows that the motion o f the CN ions in their deformed potentials remain fast. With decreasing concentration x, the influence o f the collective interactions between the CN ions become less pronounced and a gradual transition to systems with decoupled CN ions can be observed.