The variation of optical absorption edge with sintering time for the ceramic ZnO + xMnO2-Bi2O3-TiO2

Photopyroelectric spectroscopy is used to study the variation of optical absorption of the ceramic xMnO₂ - 0.4 Bi₂O₃ - 0.4 TiO₂ - ZnO, x = 0, 0.4 mol% sintered for 1 - 4 hours at the isothermal temperature, 1220 oC. The wavelength of incident light, modulated at 12 Hz, is kept in the range 310 to 810 nm. The band-gap energy is reduced from 3.2 eV (for pure ZnO) to 2.83 eV for 0 mol% MnO₂ for 1 hour sintering time and decreases further with the further increase of sintering time. E_g is decreased to 2.39 eV for 1 hour sintering time after the addition of 0.4 mol% of MnO₂ in the ceramic combination. It is reduced to a value 1.9 eV with the further increase of sintering time. The variation of steepness factor sigma_A and sigma_B which characterizes the slop of exponential optical absorption, is correlated with the variation of E_g, sintering time and doping of MnO₂. Microstructure and compositional analysis of the selected areas are analyzed using SEM and EDAX.