ELECTRICAL-CONDUCTIVITY AND DEFECT STRUCTURE OF CR2O3 .2. REDUCED TEMPERATURES (LESS-THAN-SIMILAR-TO-1000-DEGREES-C)

The electrical conductivity of Cr2O3 has been studied by the four poin t ac technique as a function of oxygen activity (O2 + Ar, CO+CO2 and H -2+H2O mixtures) in the temperature range 440-1500-degrees-C. This pap er focuses on the conductivity behaviour at temperatures below about 1 000-degrees-C. Under these conditions it is concluded that the oxide e xhibits extrinsic behaviour determined by the presence of dissolved di valent cation (Mg) impurities and accordingly the oxide is a p-conduct or. In O2 + Ar and CO + CO2 mixtures the conductivity exhibits a small oxygen pressure dependence (approximately sigma is-proportional-to P( O2)1/20), and this is interpreted to reflect slow equilibration kineti cs and a decreasing solubility of the cation impurities with decreasin g oxygen activity. In H-2 + H2O mixtures equilibration kinetics are re latively rapid and the conductivity is dependent on both the oxygen an d hydrogen activity; this demonstrates that hydrogen dissolves in chro mia and significantly affects the defect structure and electrical cond uctivity. The defect structure of chromia is discussed.