THERMAL ANOMALIES IN BI2WO6 AND EPR OF DOPED GD-3+ IONS

The dielectric constant epsilon'(omega, T), epsilon''(omega, T) and the electric conductivity sigma(omega, T) of Bi2-xGdxWO6 single crystals have been measured in the temperature range from 350 K to 4.2 K and at frequencies from 20 Hz to 1 MHz. EPR measurements with an X-band spectrometer have been made on Gd3+-doped Bi2WO6 crystals. Two kinds of centres observed are ascribed to Gd(1) and Gd(2) ions substituted for Bi(1) and Bi(2) ions, respectively. Fine structure parameters obtained are \b2(0)\ = 1367, 1138, and \b2(2)\ = 1060, 384 in units of 10(-4) cm-1. Temperature dependence of resonant fields for the Gd(1) centre shows a marked difference from that for the Gd(2) centre. This is due to the difference between the coupling of the two Gd ions to phonon modes.