Electrical Transport Processes in Beryllium Oxide

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Abstract
The electrical resistivity was determined for polycrystalline and single‐crystal BeO between 1200°–1700°C. Analysis was made of the effects of oxygen partial pressure, aliovalent impurities, and microstructure. Conductivity and relevant diffusion coefficients were calculated with these data. The results show the BeO samples to be impurity‐controlled ionic conductors, and establish the need for higher‐purity material to study intrinsic properties. Electrical migration is independent of grain boundaries and crystallographic direction. Creation of cation defects by varying the oxygen activity in the specimens is not an important process in this material. At high temperatures, above a critical roll‐over temperature determined by the impurity content, electrical transport processes occur by a vacancy mechanism with an activation energy of 65 ± 5 kcal/mole. At lower temperatures, the electrical transport process is more complex and no simple theory is applicable. It is suggested that precipitation of impurities may be a more important process than the association of vacancy–impurity complexes in this system. The activation energy for this process depends inversely on the amount of aliovalent impurities present in the sample, and has a value of 73 kcal/mole at the lowest concentration studied.

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