Electrical Characterization Of Pd-Doped Cmas-Tio2 Glass-Ceramics

Electrical characterization was performed on Pd-bearing and Pd-free, electrically conductive glass-ceramics in the CMAS-TiO2 system. AC impedance plots clearly revealed both grain-core and grain-boundary semicircles. Grain boundaries had a lower magnitude of conductivity but a similar activation energy to grain-core conduction except when Pd was present, for which much lower activation energies were indicated. The lack of any frequency (f) dependence of conductivity for f<100Hz, while using noble metal electrodes, suggests the conduction was dominantly electronic in origin in these glass-ceramics. Time-dependent polarization measurements showed no change in electrical current over several days, also consistent with this conclusion. Overall, the temperature dependence of the conductivity was relatively low over a very large temperature range, but quite complex. The appearance of a sharp minimum in conduction seen near 600 degrees C suggests some type of transition occurred with our glass-ceramics, possibly related to semiconductor-to-metal transitions seen with some transition-metal crystals. The available data suggest that Pd did have some effect on grain-boundary conduction, but that a percolating Pd network was not formed.