ANOMALIES OF HOPPING CONDUCTION AND DIELECTRIC-DISPERSION OF BI2WO6

The dielectric constant epsilon' (omega, T), epsilon" (omega, T) and the the electric conductivity sigma-(omega, T) of Bi2WO6 single crystals are measured in the temperature range from 350 to 4.2 K and at frequencies from 20 Hz to 1 MHz. The anomalous temperature dependences of sigma, epsilon', and epsilon", and the intensity of X-ray diffraction along the b-axis are observed at about 15-degrees-C. These anomalies correspond to a first order phase transition related with the impurity conduction and with the soft phonon. From the temperature dependence of s = 1 - 4/ln (nu-ph)/omega) on ac hopping conductivity sigma-(omega) proportional omega-s and dielectrinc constant epsilon" (omega) proportional omega-s-1, the softening of photon is confirmed at T(c).