Dipolar reorientation and order-disorder behavior of pure and mixed alkali cyanides

A simple empirical relation connects the critical temperature of the order-disorder transition Tc to the dipolar reorientation rate -1(T) of CN- molecules by the concept of a critical reorientation rate c-1(Tc). This relation is derived from experimental data on four pure alkali cyanides, the dipole-diluted (KBr)1-x:(KCN)x system, and the mixed alkali cyanides (KCN)1-x:(NaCN)x and (RbCN)1-x:(KCN)x. The observed disappearance of the order-disorder transition at a certain x value occurs in all mixed systems, when the spread of relaxation rates exceeds a particular value.