Comparison of molding methods for the production of high optical transmittance YAG: Yb ceramics

Abstract

This study compares four molding methods for producing transparent ytterbium-doped YAG:Yb ceramics: dry uniaxial pressing, conventional slip casting, pressure slip casting, and centrifugal casting. Using the chemical precipitation method, YAG:Yb ceramic powders were synthesized and utilized to fabricate compacts. Centrifugal casting was employed to fabricate highly-transparent YAG:Yb ceramics, and its impact on green body formation, sintering behavior, and final optical properties was systematically compared against conventional methods. The powder characteristics, green body density, shrinkage behavior, and the resulting optical transmittance and microstructure of the sintered ceramics were systematically analyzed using laser diffraction particle size analysis, BET specific surface area measurements, dilatometry, scanning electron microscopy, UV-Vis-NIR spectrophotometry, and optical microscopy. All green bodies were vacuum-sintered at 1825 °C for 10 h and subsequently hot isostatically pressed at 1700 °C and 200 MPa for 5 h. Despite producing green bodies with the lowest initial density (22.3%), centrifugal casting enabled the formation of the most isotropic particle packing with open porosity, which greatly facilitated the efficient removal of binder residues and the complete elimination of pores during sintering and hot isostatic pressing. Consequently, the ceramics fabricated by this method achieved optical transmittance values 82.1% at 400 nm and 84% at 1100 nm after HIP, compared to 79% at 400 nm for dry-pressed samples, with virtually no light-scattering defects. Before HIP, the centrifugally cast sample already exhibited the highest transmittance (82.8% at 1100 nm). This study demonstrates the strong potential of centrifugal casting for manufacturing high-quality YAG optical ceramics.