Impact of sintering temperature on the structural, electrical, and optical properties of doped ZnO nanoparticle-based discs

In the current study, 20 nm zinc oxide (ZnO) nanoparticles were used to make high-density ZnO discs doped with Bi2O3 and Mn2O3 via the conventional ceramic processing method. Different sintering temperatures were found to have significant impacts on the ZnO discs, especially on enhancing grain growth even at a low sintering temperature of only 980 °C. The strong solid-state reaction during sintering may be attributed to the high surface area of the 20 nm ZnO nanoparticles that promoted a strong surface reaction even at low sintering temperatures. Moreover, the sintering process also improved the grain crystallinity, as shown in the lowering of the intrinsic compressive stress based on the X-ray diffraction lattice constant and full-wave half-maximum data. The sintering temperatures also significantly influenced the electrical properties of the doped ZnO discs with a marked drop in the breakdown voltage from 330 V (sample at 980 °C) to 80 V (sample at 1380 °C). The resistivity also experienced a dramatic drop from 304.4 kΩ cm (sample at 980 °C) to 98.86 kΩ cm (sample at 1380 °C). The observed shift in the energy band-gap from a higher to a lower value may be attributed to the conversion of compressive stress to tensile stress with increasing sintering temperature. The Raman spectra indicate that the sintering temperatures and dopants in the discs had significant effects on the image phonon mode and ZnO crystal structures. Therefore, the sintering process can be used as a new technique for controlling the breakdown voltage of doped ZnO discs made from ZnO nanoparticles with improved structural and optical properties.