ELECTRICAL-CONDUCTIVITY AND DEFECT STRUCTURE OF MG-DOPED CR2O3

The electrical conductivity of Cr2O3 nominally doped with 2 mol% MgO h as been studied by the four point a.c. technique as a function of the oxygen activity (O-2 + Ar, CO + CO2 and H-2 + H2O) in the temperature range 400-1200 degrees C. It is concluded that Cr2O3 doped with MgO is an extrinsic conductor and that the dissolved ME-dopant is compensate d by the formation of electron holes at near atmospheric oxygen pressu res and by oxygen vacancies (or possibly interstitial chromium ions) a t highly reduced oxygen activities (in CO + CO2 and H-2 + H2O gas mixt ures). In H-2 + H2O mixtures Mg-doped chromia also dissolves hydrogen as protons and significantly affects the defect structure and electric al conductivity. The defect structure of the oxide under various condi tions is discussed.