EFFECT OF FREQUENCY ON THE ELECTRICAL CHARACTERISTICS OF TIN-ANTIMONY-OXIDE MIXTURES

The effect of frequency (100 Hz to 1 MHz) both on complex permittivity and on complex impedance data was used to study the conduction proces ses in Sn-Sb-O systems between 300 and 873 K. The conductance of tin o xide was increased by the addition of antimony oxide at all frequencie s and a peak in conductivity was observed at 5 wt % Sb2O3. The effect of frequency on conductance was in agreement with the universal behavi our of solid dielectrics, whilst the atmosphere-dependent capacitance indicated surface dipole phenomena. The catalytic activity and selecti vity patterns for the oxidation of propylene above 650 K may be correl ated with the observed electrical behaviour, which is related to the m obility of lattice oxygen in the outer layers of the surface.