ANOMALIES OF HOPPING CONDUCTION AND DIELECTRIC-DISPERSION OF BI2-XMXWO6 (M = LA, TL)

The dielectric constant epsilon'(omega, T) and the electric conductivity sigma(omega, T) of Bi2-xMxWO6 (M = La, Tl) single crystals are measured in the temperature range from 350 to 4.2 K and at frequencies from 20 Hz to 1 MHz and 9.3 GHz. Anomalies of the dielectric constant and the electric conductivity along the layer axis (b-axis) are observed in the temperature range from -30 to 30-degrees-C. These anomalies correspond to a first order phase transition related with the hopping mechanism of the impurity conduction and with the phonon. A new anomaly of epsilon'b in Bi2-xTlxWO6 single crystals is observed at 61.3 K.