Microwave and optical spectroscopy of 8 and 12 mole % yttria stabilized zirconia

Abstract

During the work, which forms the basis of this thesis, 8 and 12 mole % Yttria Stabilized Zirconia (YSZ) single crystals have been studied from the Electron Paramagnetic Resonance (e.p.r.) and Optical Spectroscopy points of view, in both the as grown state and after current blackening by current passage at several current densities. Experimental factors limited the range of current density used to between 0.1-5 A/cm(^2) for the study of optical spectroscopy and to between 1-25 A/cm(^2) for e.p.r. The e.p.r, study was made at 35 GHz, using a cavity spectrometer, at 293ºK and 77ºK. These measurements were difficult because of the low spin densities encountered and because of the cavity damping caused by blackened crystals. They showed in as grown material, the presence of an "F-Centre," (e(^-) + (0)(^..) + Y ion). This complex was also seen in blackened crystals. In addition, in both as grown and blackened crystals a second line was observed due possibly to Zr(^3)+ or Y(^2+). A third line, appearing only after current passage seemed to be more likely to arise from conduction electrons than from colour centres or paramagnetic ions. Prom optical absorption spectra the band gap energies were calculated to be 4.50 ev and 4.45 ev, at 293ºK for the 8 and 12 mole % as grown YSZ respectively. Attempts made to fit the absorption curves to the conventional formulae for semiconcluctors showed that the only near fit was for an indirect allowed transition and this only held for the tail region of the absorption edge. For absorption spectra of differently 'blackened samples, two methods (transmission-transmission and reflectivity-transmission) were applied at 293ºK. They showed that the absorption curves shifted non-linearly beyond 1.0 micron as compared with the absorption edge position for the as grown samples. An explanation of this is suggested as due to scattering of light from colloidal metallic Zr particles. From transmission spectra, made at 293ºK for both 8 and 12 mole % as grown YBZ, the Debye temperatures were calculated to be 660 ± 12 ºK and 666 ± 12 ºK respectively. Reflectivity and refractive index measurements were also made. Some general conclusions are given.