Vibrational, DSC and dielectric studies of Cs1.5Li1.5H(SO4)2 crystal

The crystal of Cs1.5Li1.5H(SO4)(2) and its deuterated derivative were obtained. The calorimetric (DSC) and vibrational studies (IR at 300-14 K, FT-Raman only at 300 K) for both crystals are performed. The DSC studies reveal that the Cs1.5Li1.5H(SO4)(2) crystal undergoes the second order phase transition at 162 K, On deuteration the phase transition shifts to a lower temperature (ca. 152 K). The structural phase transition of the superionic type follows from the dielectric measurements (500 Hz to 1 MHz) at low temperatures. The dielectric data indicate the presence of a low frequency (below 30 kHz) relaxation process. The reorientation of the active electric dipole is frozen at the temperature of the phase transition as followed from the DSC data (163 K), The reorientation rate is of the order 10(-3) s near 190 K. The vibrational spectra are discussed in relation to the crystal structure and possible conductivity and phase transition mechanism. Characteristic spectral feature (AB bands) due to a stretching nu OH mode of a medium hydrogen bond is identified. The bands due to two types of sulphate ions, HSO4- and SO4-2 are established. (C) 1999 Elsevier Science B.V. All rights reserved.