Highly Transparent Polycrystalline MgO via Spark Plasma Sintering

Optically transparent ceramics and MgO in particular are promising materials for a wide range of optical applications. This study introduces exceptionally highly transparent MgO ceramics produced via spark plasma sintering (SPS) at relatively low temperature and pressure by optimal incorporation of LiF as a sintering additive. The effect of LiF content on the microstructural and optical properties is presented with emphasis on its function as a densification aid and an agent for minimizing residual carbon contamination. Fully dense MgO discs, 20 mm in diameter and 2 mm thick, with ∼80% in-line transmission at 800 nm and >85% transmission in the infrared range (2-6 μm), are attained. These results demonstrate outstanding transparency in SPS polycrystalline MgO in the 800 nm range, only 7% below the theoretical value. In addition, this work strengthens our understanding of the LiF action mechanism during MgO sintering and its influence on texture development in the SPS-pressing direction. These findings pave the way for fabrication of large, fully dense samples with nearly theoretical transparency.