Point defects instudied by electrical conductivity, optical absorption, and ESR
- 15 March 1983
- journal article
- research article
- Published by American Physical Society (APS) in Physical Review B
- Vol. 27 (6), 3821-3841
- https://doi.org/10.1103/physrevb.27.3821
Abstract
Total and partial ionic and electronic -axis dc conductivities were measured for single-crystal :8 ppm Mg as a function of oxygen pressure and temperature. The sample is unsaturated at °C but is saturated in equilibrium with a spinel precipitate phase at lower temperatures. The results are analyzed to give ionic mobility, thermodynamic parameters of oxidation reduction of , and the solubility of MgO as a function of temperature. Oxidized samples are grayish purple due to the presence of a broad absorption band with maximum at 480 nm. Discoloration can occur by reduction (at high temperature) or by precipitation (at °C); both proceed from the surface, involving migration of oxygen out of or of Al into the crystal. An explanation for the rapid diffusion regulating precipitation below 1000 °C is proposed. Recoloration at low temperature proceeds without a front and possibly involves oxygen diffusing into the sample along dislocations or subgrain boundaries. Hole-release studies at low temperature indicate that the hole binding energy in the defect , eV. The combined results of the present work suggest that free holes move as large, rather than small, polarons and that eV.
Keywords
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