Dynamic properties and phase transitions in A2ZnBr4 (A = (CH3)4N and (CH3)4P) as studied by 79Br NQR and multinuclear NMR

In order to understand the mechanism of ferroelastic phase transitions in A(2)ZnBr(4) (A = (CH3)(4)N and (CH3)(4)P), the temperature dependences of Br-79 NQR frequencies and the spin-lattice relaxation times were measured. The temperature dependences of the H-1 and P-31 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 (similar to 100 K), the correlation times for the cation reorientation at the individual transition temperatures amount to some 10(-11) a for both compounds.