Insights into the roles of the MgO additive in crystal structures, sintering behaviors, and optical properties of transparent In2O3 semiconductor ceramics

Abstract

MgO was found to be a good sintering aid for densification of several types of ceramics; however, the previous reports seldom provided persuasive evidence to support their proposed functional mechanism. In the present work, we successfully fabricated polycrystalline transparent In₂O₃ semiconductor ceramics using MgO as an additive and offered vital insight into the additive roles in sintering behavior and optical properties, which are conducive to mastering the microstructure evolution principle and interaction function mechanism. The oxygen defect and solute drag mechanisms have combined effects on the sintering of MgO-doped In₂O₃ ceramics. Additionally, MgO also helps to improve the thermal stability. At the optimized MgO content of 0.5 at%, the In₂O₃ ceramic sintered at 1600 °C under an oxygen atmosphere achieves an in-line transmittance of 63.0% at 633 nm (∼83% of the theoretical transmittance of a perfect In₂O₃ single crystal) with a fine average grain size of ∼9.7 μm. Upon deep UV excitation, the transparent In₂O₃ semiconductors exhibit broad spectral bands covering from the near-UV to the entire visible region, where the dominant ∼493 nm cyan light derives from the deep-level defect emission. The MgO dopants enhance the photoluminescence intensity and prolong the deep-level fluorescence lifetime. The cathodoluminescence spectra show broad orange emission, with the emission centers located at 626 and 613 nm for the intra-grain and grain-boundary regions, respectively. The integral intensity of cathodoluminescence increases as the acceleration voltage increases, while the intensity in the grain interior is much higher than that on the grain boundary at each voltage.