Electrical properties of silica-alumina ceramics in nitrogen atmosphere

The SiO2–Al2O3 powders with compositions of 46.5 to 76.6 wt. % Al2O3, synthesized by the hydrolysis of metal alkoxides, were sintered at 1700 °C for 3 h in a reduced pressure of 40 Pa. After sintering, the samples were annealed at 1300 °C for 10 h in air. The densities of sintered samples were higher than 97.0% T.D. The electrical conductivities of the SiO2–Al2O3 ceramics in N2 atmosphere (>99.99%) were measured in the temperature range of 500° to 800 °C by using ac bridge circuit at 120 Hz to 1 MHz and dc circuit at 1 V. The electrical conductivities at 800 °C were 3.4 × 10−7 to 4.3 × 10−6 S cm−1, and decreased with increasing Al2O3 content. The SiO2–Al2O3 ceramics were mixed conductors of oxygen ions and electrons in nitrogen atmosphere. The activation energies of ionic and electronic conductivities were 102 to 143 kJ/mole and 102 to 123 kJ/mole, respectively.