Study on the phase transition of K3DxH1-x(SO4)(2) by the Raman scattering of the internal nu(2) mode

Temperature dependence of the nu(2) mode in mixed crystals K3DxH1-x(SO4)(2) was studied by Raman scattering from room temperature to 20K. The nu(2) modes of both HSO4- and DSO4- ions are observed separately. The frequency shift of HSO4- ion, omega(HSO4), below T-c depends on temperature as (1-(T/T-c))(beta) with beta = 0.25 +/- 0.05 when it is measured from the frequency at T-c. A discrete change in the frequency of DSO4- just below T-c is observed in the mixed crystals and its origin is explained in relation to the interaction among dimers. The temperature dependence of the anomalous broadening of the linewidth above T-c is explained well by a mechanism similar to the motional narrowing effect in NMR.