High Temperature Electrical Conductivity of Aluminum Nitride.

The total electrical conductivity of oxygen-doped and beryllium-doped aluminum nitride has been measured in the temperature range from 800(DEGREES)C to 1200(DEGREES)C in environmental nitrogen partial pressures from 10('-3) atmospheres to one atmosphere. The electronic partial conductivity of oxygen-doped aluminum nitride was measured under these same conditions by a polarization technique to determine the suitability of the material for solid electrolyte applications. The total electrical conductivity measurements were made by the four-pole D.C. method on samples doped with oxygen and with both beryllium and oxygen. The samples were hot-pressed polycrystalline material. Conductivity was observed to decrease with the addition of beryllium. In all cases, conductivity was observed to be independent of nitrogen partial pressure. The activation energy for conduction in oxygen-doped aluminum nitride was 1.45 eV, while in aluminum nitride doped with beryllium and oxygen it was 1.83 eV. Analysis of the conductivity results in terms of defect chemistry models indicates extrinsic electrons, or, intrinsic or extrinsic aluminum vacancies as the predominant carrier species in oxygen-doped aluminum nitride. The partial electronic conductivity of oxygen-doped aluminum nitride was measured under the same conditions of temperature and nitrogen partial pressure using a cell with one electrode reversible to both ionic and electronic species and one electrode blocking to ionic species. Examination of the transient and steady-state values obtained, and comparison of these results with those obtained from a known solid oxide electrolyte indicated an electronic transference number near unity. Analysis of the polarization results in conjunction with the total conductivity measurements shows that extrinsic electrons are the predominant conducting species and that either the oxygen impurity or a defect compensating the oxygen impurity acts as a donor.PhDMaterials scienceUniversity of Michiganhttp://deepblue.lib.umich.edu/bitstream/2027.42/159068/1/8225029.pd