High‐Temperature Conductivity and Creep of Polycrystalline AI2O3Doped with Fe and/or Ti

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Abstract
Partial ionic and electronic dc conductivities and compressional creep rate were measured for hot‐pressed poly crystalline AI2O3made from AI‐isopropoxide (AI2O3(II)). The undoped material was found to contain 1.5×1018cm−3fixed valency acceptors (Mg). Properties of undoped material and material doped with Fe or Ti were investigated as a function of grain size, dopant concentration, oxygen pressure, and temperature. No fast ionic conduction along grain boundaries is found in either acceptor‐ or donor‐dominated material. Absolute values of self‐diffusion coefficients calculated from conductivity and creep indicate that both effects are limited by migration of AI, involvingVAI“in donor‐, AI,” in acceptor‐dominated material. In creep, oxygen is transported along grain boundaries in a neutral form (Oip). ThepO2dependence of σtand σhare as expected on the basis of a defect model. That of creep is weaker for reasons that are not entirely clear. An ionic conductivity with low activation energy, observed at low temperature, is attributed to the presence of AI‐silicate second phase.

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