PHOTOTHERMAL STUDY OF ZnO CERAMIC DOPED WITH TiO2

Abstract

Photopyroelectric spectroscopy (PPES) is a useful tool for examining non-radiative de-excitation in semiconductor materials. The ceramic (ZnO-x, x = 0.4-2.7 mol % of TiO2) was sintered at an isothermal temperature of 1270 °C for 1 and 2 hours to investigate its optical properties. The PPES is used to study the energy band gap of this ZnO system with reference to TiO₂ doping level. The energy band-gap obtained from photopyroelectric spectrum is about constant at 2.82 eV for the samples sintered for 2 hour at all TiO₂ doping levels except at 0.4 mol.% which is 2.78 eV. The energy band gap decreases with the decrease of sintering time from 2 to 1 hour at all doping levels and is about constant at 2.79 eV for the sintering time of 1 hour except that at 0.6 mol.% level which is 2.84 eV. The steepness factors σ_A and σ_B which characterize the slop of exponential optical absorption are discussed with reference to the TiO₂ doping level. The X-ray diffractrometry shows that the crystal structure of ZnO doped with different TiO₂ mol% remains to be of hexagonal type. Microstructure and compositional analysis of the selected areas are analyzed using SEM and EDAX. The maximum relative density 95.16 % is obtained for the ceramic. The grain size is about constant at 26.8 – 311.6 µm up to 1 mol % of TiO₂ and then decreases with the increase of TiO₂ mol % indicating the excess TiO₂ suppresses the grain growth.