Fabrication, microstructure and magneto-optical properties of Tb3Al5O12 transparent ceramics

Terbium aluminum garnet (Tb3Al5O12, TAG) transparent ceramics were fabricated by the solid-state reactive sintering of a mixture of commercial Tb4O7 and α-Al2O3 powders with tetraethoxysilane (TEOS) and MgO as sintering aids. Samples sintered at 1700 °C and 1725 °C for 20 h were utilized to examine the phase compositions, optical quality, microstructure and magneto-optical property. X-ray diffraction (XRD) results show that the sample sintered at 1700 °C has a pure garnet crystal structure, while the characteristic diffraction peaks of TAG disappear when sintered at 1725 °C. The sample sintered at 1725 °C shows high transparency and the optical transmittance is beyond 80% in the region of 600-1500 nm. It is found that the sample sintered at 1700 °C exhibits homogeneous grains with the average size of about 5.97 μm, however, no TAG grains are observed in the sample sintered at 1725 °C. The Verdet constants of the samples sintered at 1700 °C and 1725 °C are −179.4, −179.3 rad T−1 m−1 at 633 nm, respectively. The thermal depolarization of the sample sintered at 1725 °C increases up to 2 × 10−4 at maximum laser power of 91 W, which corresponds to the isolation ratio of 37 dB.