Photothermal Study of ZnO Nanoparticle-Bi2O3-Mn2O3 Ceramics Doped with Different Compositions from Al2O3 at Various Sintering Temperatures

In this work, the optical absorption behavior of ZnO nanoparticle–Bi 2 O 3 –Mn 2 O 3 doped with different compositions of Al 2 O 3 at various sintering temperatures was investigated using photopyroelectric spectroscopy (PPE). Different Al 2 O 3 concentration and sintering temperatures affect significantly the varistor characteristics, predominantly promoting ZnO growth at a lower amount of Al 2 O 3 . However, the addition of larger amounts of Al 2 O 3 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 Al 2 O 3 amounts and sintering temperature. X-ray diffraction measurements provided that Al 2 O 3 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% Al 2 O 3 and sintered through different temperature is obtained by PPE. Optical energy band gap (E g ) was constant at approximately 2.51 eV for 950 °C sintering temperature during all dopant compositions. The energy of band gap reduces in varistors doped with 0.5 mol% Al 2 O 3 doping amount and sintered at 1050 and 1200 °C temperatures. With further increase in Al 2 O 3 up to 1.0 mol%, the value of E g was 2.15 and 2.21 eV for 1200 °C and 1050 °C, respectively. The superior nonlinearity value ( α ) is approximately 58 for 950 °C sintered temperature at various adding concentrations. However, at higher sintering temperatures, α value decreases with of the increase in Al 2 O 3 doping concentrations; the value becomes constant beyond 1.0 mol%. The slope of exponential optical absorption is distinguished by steepness factors “ σ A ” and “ σ B ,” which are investigated to determine the difference in the energy band gap.