Effect of Zr4+ and Ca2+ aliovalent co-doping on the microstructure and optical quality of Tb2O3-based magneto-optical transparent ceramics

Tb 2 O 3 -based transparent ceramics are promising for laser-system Faraday isolators due to their excellent magneto-optical properties. However, residual porosity from sintering impairs optical quality, thus limiting the practical application. This core challenge derives from the intrinsic trade-off between pore elimination and grain growth. In this work, an aliovalent Zr 4+ /Ca 2+ co-doping strategy was adopted to regulate densification and grain-boundary migration. The Tb 2 O 3 -based ceramics were fabricated using pre-sintering followed by hot isostatic pressing. Microstructural characterization confirmed that Zr 4+ inhibited excessive sintering grain growth, while Ca 2+ promoted ceramic densification. The optimized ceramic doped with 1.0   at.% Zr 4+ and 0.18   at.% Ca 2+ achieved high in-line transmittances of 79.67% at 1064   nm and 75.39% at 650   nm. The Verdet constant at 650   nm was −366.85   rad·T −1 ·m −1 . These results demonstrated that Zr 4+ /Ca 2+ co-doping effectively promoted pore elimination while controlling grain growth, thereby improving the optical quality of Tb 2 O 3 -based magneto-optical ceramics.