Reduction and Radiation Effects in Lithium Tantalate

Single crystals of LiTaO3 are reduced, in a vacuum at temperatures up to 1100 °C, and are electron irradiated at 77 K. Electron spin resonance spectra of Fc3+, Cr3+, and Mn2+ impurity ions and the infrared absorption of OH− molecules are monitored as a function of increasing vacuum-anneal temperature. Electron irradiation of oxidized samples produces a broad optical absorption band centered at 470 nm and a corresponding hole like ESR spectrum with gc = 2.0224. Those latter spectra become thermally unstable in the 100 to 200 K range. Differences between LiTaO3 and LiNbO3 are noted.