Influence of germanium concentration on the microstructure and optical transparency of terbium gallium garnet ceramics

In recent years, transparent terbium gallium garnet (TGG) ceramics have garnered significant interest for their application in high-power Faraday isolators. However, challenges in achieving high transparency have led researchers to explore the addition of various sintering aids as a key strategy to enhance the optical quality of TGG ceramics. Through this work, the effect of germanium (Ge) addition on the microstructure and optical transparency of TGG magneto-optical ceramics was investigated. TGG powders were synthesized by the co-precipitation method, and the source Ge was Ge ethoxide added through a ball-milling step. Transparent TGG ceramics were prepared by air pre-sintering combined with hot isostatic pressing post-treatment and subsequent annealing. The ceramics containing 200 ppm Ge exhibit optimal transmittance of 81.3% at 1064 nm (a value of theoretical transmittance), the Verdet constant was −133.0 rad·T⁻¹·m⁻¹ at 633 nm. When the addition of Ge reaches 600 ppm, a secondary phase can be observed on the surface of ceramic. Subsequently, TGG ceramics prepared from 1425°C to 1500°C with 200 ppm of Ge were analyzed, which revealed that the optimal pre-sintering temperature is 1450°C.