Photopthermal Study of Ceramic ZnO Doped with Y2O3

A powerful tool, photopyroelectric spectroscopy, for examining the optical properties as non-radiative recombination for the semiconductor materials is used for the Y₂O₃ doped ZnO ceramics. The ceramic (ZnO-x, x=0.4-1.6 mol% of Y₂O₃) was sintered at isothermal temperature, 1175 and 1275degC for 1 hour to investigate its optical properties. The PPE spectroscopy is used to study the energy band-gap of the ceramic. The wavelength of incident light, modulated at 9 Hz, is kept in the range of 300 to 800 nm and the photopyroelectric spectrum with reference to the doping level is discussed. The band-gap energy is estimated from the plot (phv)² vs hv and is about constant at 2.82 eV for the samples sintered at 1275degC at all doping levels of Y₂O₃. The energy band-gap decreases from 2.88 to 2.82 eV with the decrease of Y₂O₃ mol% at the sintering temperature of 1175degC. The steepness factor sigma_A (in A region) and sigma_B (in B region) which characterizes the slop of exponential optical absorption is discussed with reference to the doping level of Y₂O₃. The X-ray diffractrometry shows that the crystal structure of ZnO doped with different mol% of Y₂O₃ remains to be of hexagonal type and the secondary phase is Yttrium-rich. Microstructure and compositional analysis of the selected areas are analyzed using SEM and EDAX which shows the Yttrium-rich phase coexist in the grain boundaries and nodal points. The relative density is decreased with the increase of Y₂O₃ mol% indicating the increase in porosity. The grain size decreases with the increase of Y₂O₃ mol% which shows that Y₂O₃ acts as a grain inhibitor.