Dynamic Properties and Phase Transitions in A2ZnBr4 (A= (CH3)4N and (CH3)4P) as Studied by Br NQR and Multinuclear NMR*

In order to understand the mechanism of ferroelastic phase transitions in A2ZnBr4 (A = (CH3)4N and (CH3)4P), the temperature dependences of Br NQR frequencies and the spin-lattice relaxation times were measured. The temperature dependences of the 'H and P spin-lattice relaxation times were measured as well for a possible correlation between the cation dynamics and the phase transition. Although the phase transition temperatures of these two compounds differ much (-100 K), the correlation times for the cation reorientation at the individual transition temperatures amount to some 10~" s for both compounds.