Highly Transparent Polycrystalline MgO via Spark Plasma Sintering

Optically transparent ceramics have attracted significant attention for their potential in optical applications. Magnesium oxide (MgO) is a material of interest due to its high thermal stability and optical clarity. Prior research has shown that achieving full density and high transparency in polycrystalline MgO remains a challenge. Conventional sintering methods often require high temperatures and pressures, which can introduce defects and reduce optical quality. This gap motivated the exploration of alternative sintering techniques. Spark plasma sintering (SPS) has emerged as a promising method for producing dense ceramics with controlled microstructures. However, the role of sintering additives in achieving both optical transparency and mechanical integrity is not fully understood. This paper's contribution lies in demonstrating how LiF can serve as an effective sintering additive. The study addresses the need for scalable fabrication of transparent MgO ceramics with minimal contamination.

The aim of this study is to produce highly transparent polycrystalline MgO ceramics using spark plasma sintering. The specific problem addressed is the challenge of achieving full density and high optical transparency in MgO. The motivation stems from the demand for optical materials that can perform in harsh environments. The researchers propose that LiF can act as a densification aid while reducing residual carbon contamination. The study seeks to understand how LiF affects microstructural and optical properties. By optimizing LiF content, the team aims to enhance transparency and texture development. The goal is to fabricate large, fully dense MgO samples with near-theoretical optical performance. This work could lead to improved optical components for industrial and scientific applications.

The study employs spark plasma sintering (SPS) to fabricate MgO ceramics. The process involves pressing MgO powder with varying LiF content. The sintering is performed at relatively low temperatures and pressures. The researchers use LiF as a sintering additive to promote densification. The microstructural evolution is analyzed using optical and scanning electron microscopy. Transmission measurements are conducted in the visible and infrared ranges. The effect of LiF on texture development is also investigated. The samples are characterized for in-line transmission and thickness. The study compares the optical properties of samples with different LiF concentrations.

The highest transparency is achieved with 0.5 wt% LiF additive. MgO discs with 80% in-line transmission at 800 nm are produced. Transmission in the infrared range exceeds 85% between 2-6 μm. These values are only 7% below the theoretical maximum for MgO. The samples are fully dense with a thickness of 2 mm and diameter of 20 mm. LiF is shown to reduce residual carbon contamination effectively. The study confirms LiF's role in promoting densification during SPS. Texture development is influenced by the pressing direction during sintering.

The authors report that LiF enhances the optical and microstructural properties of MgO ceramics. The findings suggest that LiF acts as both a densification aid and a contamination reducer. The study confirms the feasibility of producing large, fully dense MgO samples via SPS. The results indicate that LiF content significantly affects transparency and texture. The authors propose that optimizing LiF concentration is key to achieving high optical quality. The work demonstrates that SPS can produce MgO with near-theoretical transparency. The study supports the potential of LiF-doped MgO for optical applications. These conclusions align with the observed microstructural and optical data.