Fabrication And Properties Of Terbium Aluminum Garnet(TAG) Magneto-optical Ceramics By Reactive Sintering

The magneto-optical isolators play a very important role in the fields of laser,optical information processing,fiber-optic communication and so on.Its working principle is based on the Faraday effect of magneto-optical materials.The main role of the optical isolators is to isolate the reflected light in the optical path,reduce the interference to the light source and improve the working stability of the system.Terbium aluminum garnet(Tb₃Al₅O₁₂,TAG)shows superior properties of Verdet constant,isolation and thermal polarization than those of the terbium gallium garnet(Tb₃Ga₅O₁₂,TGG)single crystal when obtaining the same optical quality.It can meet the application requirements of kilowatt-level laser systems and provide a new possibility for the development of magneto-optical devices in the visible and near-infrared regions.TAG magneto-optical transparent ceramics can effectively solve the issue that the composition deviates from the stoichiometric ratio due to the incongruent melting during the single crystal growth.In addition,the ceramics have the advantages of short preparation cycle,small size limitation and high fracture toughness.With the development of ceramics preparation technology,the application prospects of TAG magneto-optical transparent ceramics are wider.Based on the above research background,the raw material powders were pretreated in air and the TAG magneto-optical ceramics were fabricated by solid-state reactive sintering and hot isostatic pressing?HIP?post-treatment.The influences of powders calcination temperature and sintering aids content on the properties of TAG ceramics were investigated.The main works of this paper are as follows:?1?Using commercial nano Tb₄O₇ and submicron?-Al₂O₃ powders as raw materials,TAG magneto-optical transparent ceramics were fabricated by solid-state reactive sintering.The influences of phase transformation during the reactive sintering and the calcination temperature on the morphology of mixed powders were studied.The powders calcined at 1400°C and above were in pure TAG phase.Considering the low sinterability of the powder calcined above 1100°C,TAG magneto-optical transparent ceramics were prepared by vacuum pre-sintering and HIP post-treatment using mixed powders calcined at 600-1100°C.The influence of powder calcination temperature on the optical quality of TAG ceramics was studied.The results showed that there was no significant difference in the optical quality of TAG ceramics prepared using mixed powders calcined at 600-900°C.The optical quality of TAG ceramics prepared from powders calcined above 1000°C was significantly reduced.?2?The influences of TEOS as sintering aid on the densification,microstructure,optical quality and magneto-optical properties of TAG ceramics were investigated.The densification rate and the average grain size of TAG ceramics increased with the increasing TEOS amount.When pre-sintered at 1700°C,the influences of TEOS additions and holding time on the microstructure and optical quality of TAG ceramics were studied.The results showed that the transmittance of TAG ceramics in the visible wavelength range could be improved significantly by prolonging the holding time.The best in-line transmittance of 66%in the visible and near-infrared regions was obtained for the TAG ceramic pre-sintered at 1700°C for 20 h and HIP post-treated at1700°C for 3 h under 176 MPa argon gas with 0.2 wt.%TEOS as sintering aid.The Verdet constant of the TAG transparent ceramics at 633 nm was measured to be-178.7 rad·T^-1·m^-1,which was 1.3 times higher than that of the commercial TGG single crystals(-134.1 rad·T^-1·m^-1).