Study of the molecular dynamics and phase transitions of (, Rb, and Cs) single crystals

The spin–lattice relaxation time of the 1H nuclei in the ammonium groups in (NH4)2ZnCl4 crystals has been measured as a function of temperature for a range of temperatures that includes those of the phase transitions. The temperature dependence of this relaxation time is more or less continuous near T C , and is not affected by the phase transitions. A minimum was found in the 1H spin–lattice relaxation time that is related to NH4+ tunneling. Our results for (NH4)2ZnCl4 are compared with previously reported results for Rb2ZnCl4 and Cs2ZnCl4 crystals. The differences between the atomic weights of NH4, Rb, and Cs are responsible for the differences between the molecular motions and phase transitions of these single crystals.