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 obtai ned. The calorimetric (DSC) and vibrational studies (IR at 300-14 K, FT-Ram an only at 300 K) for both crystals are performed. The DSC studies reveal t hat the Cs1.5Li1.5H(SO4)(2) crystal undergoes the second order phase transi tion at 162 K, On deuteration the phase transition shifts to a lower temper ature (ca. 152 K). The structural phase transition of the superionic type f ollows from the dielectric measurements (500 Hz to 1 MHz) at low temperatur es. 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 sp ectral feature (AB bands) due to a stretching nu OH mode of a medium hydrog en bond is identified. The bands due to two types of sulphate ions, HSO4- a nd SO4-2 are established. (C) 1999 Elsevier Science B.V. All rights reserve d.