Abstract
In this work, the optical absorption behavior of ZnO nanoparticle-Bi2O3-Mn2O3 doped with different compositions of Al2O3 at various sintering temperatures was investigated using photopyroelectric spectroscopy (PPE). Different Al2O3 concentration and sintering temperatures affect significantly the varistor characteristics, predominantly promoting ZnO growth at a lower amount of Al2O3. However, the addition of larger amounts of Al2O3 inhibits the grain growth by the increasing amount of spinel phase. The large surface properties of the nanoparticles enhanced the surface interactions even at minimal sintering temperatures. The density is increased depending on increasing the Al2O3 amounts and sintering temperature. X-ray diffraction measurements provided that Al2O3 additive to ceramics leads to construction of the pyrochlore and spinel phase during the sintering process at various temperatures. The energy band gap (E-g) of nanoparticle powder added with 0.0 mol% to 3.0 mol% Al2O3 and sintered through different temperature is obtained by PPE. Optical energy band gap (E-g) was constant at approximately 2.51 eV for 950 degrees C sintering temperature during all dopant compositions. The energy of band gap reduces in varistors doped with 0.5 mol% Al2O3 doping amount and sintered at 1050 and 1200 degrees C temperatures. With further increase in Al2O3 up to 1.0 mol%, the value of E-g was 2.15 and 2.21 eV for 1200 degrees C and 1050 degrees C, respectively. The superior nonlinearity value (alpha) is approximately 58 for 950 degrees C sintered temperature at various adding concentrations. However, at higher sintering temperatures, alpha value decreases with of the increase in Al2O3 doping concentrations; the value becomes constant beyond 1.0 mol%. The slope of exponential optical absorption is distinguished by steepness factors "sigma (A)" and "sigma (B)," which are investigated to determine the difference in the energy band gap.