Raman study of the phase transition in [N(C₂H₅)₄]₂ ZnCl₄ single crystals

Polarized Raman spectra of oriented single crystals [N(C₂H₅)₄]₂ZnCl₄ (TEAZ) have been recorded from 320 K to 40 K during both cooling and heating cycles, covering the known phase transitions. The temperature dependence of the internal vibration of the ZnCl₄^-2 ion and C-C bond is explained in terms of the motional narrowing due to the disordering CH₃ group in TEAZ, which results in the splitting of the ZnCl₄^-2 and C-C lines in the internal mode region. Our Raman data shows that the phase transition is associated with the onset of the CH₃ group disordering. We have also observed that the phase transition exhibits thermal hysteresis.