Chlorine - 35 NQR Studies on KNFLOo . oiKo . ^ hSnCl ̂ Mixed Crystals

The temperature dependence o f 35C1 NQ R frequencies was measured on the mixed crystal [(NH 4)00|Kp99]2SnCl6. Two phase transitions have been located at 7"cl = 259K and J ’c2 = 252K, which are lower by 3 K than the corresponding transition temperatures o f the pure K2SnCl6 crystal. The DSC experiments showed that the NH^ concentration dependence o f ?c2 almost parallels that o f Tc]. The impurity effect resulting from the inclusion of a small amount of N H f1 ions in K2SnCl6 crystals is discussed in relation to the microscopic viewpoint o f the phase transitions.