ESR measurements of the oxygen vacancy Vo+ were performed on undoped ZnO ceramics and on Bi2O3-doped ZnO ceramics additionally heat-treated in reducing atmosphere. The temperature dependences of the relative signal intensity and the line width of the ESR signal were investigated in both the samples. By the measurement of the temperature dependent relative intensity of the ESR signal of the Vo+ center the ionization energy of the Vox center was obtained. An analysis of the temperature dependence of the line width of the ESR signal of the Vo+ center in the Bi2O3-doped ZnO ceramics showed that Vo+ centers produced by reducing subsequent heat treatment were localized at the boundary layer of the ZnO grains in high local concentrations.

ESR Investigation of the Oxygen Vacancy in Pure and Bi2O3-Doped ZnO Ceramics. Pöppl, A., Völkel, G.: Physica Status Solidi A, 1989, 115[1], 247-55