Effects of M2O3-Y2O3 (M = Sc and Al) additives on electrical conductivity of hot-pressed SiC ceramics

Highly densified silicon carbide ceramics were fabricated by hot-pressing beta-SiC powders with Sc2O3-Y2O3 and Al2O3-Y2O3 additives. The Sc2O3 and Al2O3 contents of the additives were varied while maintaining a constant Y2O3 content. For the same Y2O3 content (0.849 wt%), the electrical conductivity (sigma) of the ceramics decreased to 2.3 x 10(2), 4.5 x 10(1), and 5.3 Omega(-1) cm(-1) with an increase in the Sc2O3 content to 0.259, 0.519, and 1.038 wt%, respectively. Similarly in the case of Al doping, the sigma of the ceramics decreased to 1.2, 7.9 x 10(-1), and 1.2 x 10(-1) Omega(-1) cm(-1) with an increase in the Al2O3 content to 0,219, 0,437, and 0.874 wt%, respectively, at a fixed Y2O3 content of 0.967 wt%. This decrease in sigma can be primarily attributed to the increase in the concentration of the deep acceptors generated by Sc or Al doping in the SiC lattice. The Sc-Si and Al-Si acceptors compensated the N-C donors, leading to a decrease in the carrier density of the ceramics. The lower sigma of the Al-doped specimens than that of the Sc-doped ones can be attributed to their lower carrier mobility.