PROTONS AND OTHER DEFECTS IN FE-DOPED KTAO(3)

The properties of defects in Fe-doped KTaO3, both in the form of single crystals and polycrystalline ceramics, have been investigated for a wide range of Fe concentrations. The techniques employed included infrared (IR) absorption, electron paramagnetic resonance (EPR), and ac electrical conductivity together with complex-impedance analysis. Samples were pretreated (at 900-degrees-C) in water vapor to introduce protons which take the form of OH(O). defects, and were also treated at various oxygen partial pressures. A calibration of the OH- IR absorption band was carried out with the aid of a deuterium nuclear-probe method. EPR showed cubic and axial Fe3+ spectra, but only the axial spectrum appeared for crystals with high Fe concentrations. Predominantly proton conductivity was observed for samples treated in reducing atmospheres, and a proton-hopping activation energy of 0.73 eV was deduced. For samples treated in high oxygen pressures, however, hole conduction dominated. Evidence for proton interaction effects was also found, but the nature of the traps is not clear.