Photothermal study of ceramic ZnO doped with MnO

The band-gap energy (E_g) of ZnO doped with 0.1 to 2.0 mol % MnO and sintered at various isothermal sintering temperature is studied by photopyroelectric spectroscopy (PPES). The incident light was modulated at a frequency of 9Hz and was scanned in the wavelength range of 300 nm to 800 nm. E_g is estimated from the plot (phv)² vs hv and is about 3.0 eV for the samples sintered at 850 C at all doping levels. Samples sintered at higher temperatures, the value of E_g decreases with the MnO mol % and beyond 1mol % E_g becomes constant at about 2.0 eV. The maximum value of nonlinear coefficient (α) of I-V characteristics is low for the samples sintered at 850 C at all doping levels. For the samples sintered at higher temperatures a decreases from the high initial values with the increase of MnO mol %; beyond 1 mol % it becomes constant. The X-ray diffractrometry shows that the crystal structure of ZnO doped with different mol % of MnO at all sintering temperatures remains to be of hexagonal type but a small peak is found related to the new phase ZnMn₂O₄ only at 1050 C sintering temperature at 2 mol % of MnO doping level. The density is decreased from 95.5% to 87% with the increase of sintering temperature and doping level.