Fabrication and properties of non-stoichiometric Tb₂(Hf_1–xTb_x)₂O_7–x magneto-optical ceramics

Non-stoichiometric Tb₂(Hf_1−xTb_x)₂O_7−x (x = −0.07–0.45) magneto-optical ceramics were fabricated by solid-state reactive sintering in vacuum combined with hot isostatic pressing (HIP) post-treatment without any sintering aids. The phase composition, densification process, microstructure, optical transmittance, and Verdet constant of Tb₂(Hf_1−xTb_x)₂O_7−x ceramics were investigated. The in-line transmittance of (Tb_0.93Hf_0.07)₂Hf₂O_7.07 ceramics with a thickness of 2.0 mm reaches 74.6% at 1064 nm. The Verdet constant of Tb₂(Hf_1−xTb_x)₂O_7−x ceramics is −153.4, −155.8, and −181.2 rad/(T·m) at the wavelength of 633 nm when x = −0.07, 0, and 0.1, respectively. The Verdet constant increases with the increase of Tb content, and these values are higher than that of the commercial Tb₃Ga₅O₁₂ crystal, indicating that non-stoichiometric Tb₂(Hf_1−xTb_x)₂O_7−x ceramics have a great potential for the application in Faraday isolators.