The cesium-ammonium dihydrogen arsenate (CADA-x, x=0.20) mixed crystal was studied by the temperature dependent Raman scattering spectra to understand the microscopic origins for anomalies associated with the dipole glass freezing phenomena in the system. A$_1$ symmetry internal vibrations of arsenate ions were found to deviate from the normal temperature dependence of the 3rd and 4th order anharmonic phonon-phonon interactions at around $T_f \simeg 80K$, which was ascribed to the onset of the short range random potential fixing of protons around the tetrahedral $AsO_4$ units. The $B_2$ symmetry soft-mode derived from the harmonic oscillator coupled mode analysis was found to be a relaxational type characterized by $\omega^2/\gamma\propto(T-T_o$) with $T_o \simeg 28.8K$, where $\omega^2/\gamma$ corresponds to the relaxation bandwidth of the soft-mode. The large difference between the two anomaly temperatures was attributed to the enhanced effective piezoelectric constant associated with the electrostrictive contributions from the random local cluster polarizations. In E symmetry modes temperature dependence of internal vibrations of arsenate ions is similar to that of $A_1$ symmetry modes except hardening of the Raman frequency below 80K. Low-frequency external mode is more prominent in the case of z(xz)x geometry.
The dielectric dispersion measurements of CADA-0.20 mixed crystal were carried out in the temperature range from 200K to 15K and in the frequency range from 0.1Hz to 1MHz. Tikhonov regularization method was applied in the analysis of the experimental data to get the relaxation time distribution g(τ). Temperature dependence of g(τ) was examined to observe a weighting factor variation from high frequency relaxor-side at the high temperature to low-frequency relaxor-side at low temperature. The g(τ) distribution was much broader than that of DRADP $(Rb_{1-x}(ND_4)_xD_2PO_4)$ system.
We have measured the polarized Raman spectra of cesium dihydrogen phosphate (CDP) single crystal in the temperature range from 300K to 25K. $A_g$ symmetry symmetric stretching mode $\nu_1$ and antisymmetric stretching mode $\nu_3$ of arsenate ions were found to have highly asymmetric Raman band profiles. The asymmetric Raman bands were fitted to Breit-Wigner-Fano resonance line shape associated with coupling between a discrete phonon state and possibly a phonon density contninuum. The intensity to obtain from the best fit parameters show anomalous temperature dependence around phase transition temperature. In $B_g$ symmetry spectra temperature dependence of $\nu_4$ bending modes was found to indicate an anomaly around phase transition temperature in both Raman frequency shift and band width.
