Temperature-dependent band gap renormalization in ZnO ceramics sintered using concentrated solar energy

The solar furnace enables the rapid sintering of ceramics, but the underlying mechanisms affecting optical absorption at elevated temperatures remain to be investigated. This study investigates the temperature-dependent band structure of ZnO crystals and its impact on the optical absorption of solar-sintered ZnO ceramics. The quasiparticle band gap of ZnO is calculated using the G0W0 approximation. The renormalization effects due to electron-phonon interactions and lattice thermal expansion are evaluated using ab initio methods. The results demonstrate that the band gap renormalization is primarily attributed to electron-phonon interactions. The calculated reduction in the band gap with increasing temperature agrees with that extracted from diffuse reflectance spectra of solar-sintered ZnO ceramics. Shifting the absorption edge toward longer wavelengths at higher temperatures enhances the ceramic absorption in the solar spectrum range. This study provides fundamental insights into the optical absorption properties relevant to photon-driven sintering technology.