A team of material scientists led by Jiang Li from Shanghai Institute of Ceramics, Chinese Academy of Sciences, in Shanghai, China recently reported (Tb_1-xSc_x)₃(Al_1-ySc_y)₂Al₃O₁₂ (TSAG) magneto-optical ceramics with high optical quality. The effect of Sc substitution on the crystal structure, sintering process, microstructure, optical transmittance, and magneto-optical property of the TSAG ceramics is studied in detail. Antisite defects (ADs) and Sc replacement in TAG are further studied by first-principles calculations to figure out the working mechanism of Sc. It was found that Sc can suppress the secondary phase and improve the optical quality of TAG ceramics. As optical quality occupies one of the most important parts of the practical performance of magneto-optical ceramics, Sc₂O₃ is considered to be a promising and effective additive.

The team published their research article in Journal of Advanced Ceramics (DOI: 10.26599/JAC.2024.9220948) on August 1, 2024.

In high-performance laser devices, Faraday isolators are one of the important components that can prevent the front-end system from disturbance and damage caused by a back-reflected beam. Magneto-optical materials are thus widely studied as they are key elements of Faraday isolators. Among magneto-optical materials applied in the visible to near-infrared wavelength band, TAG ceramics have been considered to be one of the most promising materials thanks to their high Verdet constant and good thermo-optic properties. However, the manufacturing process of TAG ceramics should be further optimized to reduce the optical loss and make them applicable for practical use. Optical scattering from the secondary phases is one of the most important problems for TAG ceramics, originated from the narrow solid-solution range.

Based on the existing problems and difficulties of TAG ceramics, the research team proposed their own solutions. “If Sc³⁺ tends to occupy both Tb³⁺ and Al³⁺ sites, it is possible that a slight deviation of Tb/Al ratio will not bring secondary phase in TAG ceramics after adding sufficient Sc³⁺, because the Sc³⁺ might ‘automatically’ fill either of the vacant sites,” said Jiang Li, senior author of the research paper, vice director of the Transparent Ceramics Research Center, Shanghai Institute of Ceramics, Chinese Academy of Sciences. Dr. Li is also a professor in Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences.

“The mechanism of Sc₂O₃ eliminating the secondary phases in TAG was discussed by combining the experiment and calculations. The results indicate that Sc₂O₃ is an effective additive for improving the optical quality of TAG ceramics,” Jiang Li said.

The result is that Sc₂O₃ improves the optical transmittance of the ceramics by suppressing the secondary phase, thanks to the increase of solubility. “The in-line transmittance of the TSAG ceramics reaches 82.2% at 1064 nm and 81.2% at 633 nm, which are close to the theoretical transmittance of TAG. No secondary phase or residual pores can be detected by FESEM,” said Jiang Li.

“To figure out the solubility of TAG, the limit of Sc replacement, and to further understand the mechanism of Sc₂O₃ suppressing secondary phases, first-principles calculations on antisite defects (ADs) and Sc replacement were performed,” said Jiang Li,“ The range of Tb/Al becomes 0.5332~0.9747 at 2023 K after Sc substitution with adequate quantity, which is much wider than that in TAG (0.6000~0.6027) calculated from ADs. The solid-solution range of TAG can be enlarged and the secondary phase can be suppressed by Sc doping, no matter which component is excess. Conceivably, Sc₂O₃ will be an effective additive for the stability of optical quality of the ceramics in mass production.”

The research team also found the side-effects caused by Sc substitution. “As the concentration of magneto-optical ion (Tb³⁺) decreases with increasing Sc content, the Verdet constant decreases from -188.1 rad·T^-1·m^-1 to -161.4 rad·T^-1·m^-1 at 633 nm. All the values are higher than that of the commercial TGG (-136 rad·T^-1·m^-1) and TSAG crystals (-152 rad·T^-1·m^-1), and the results show that Sc₂O₃ is an effective additive improving the optical quality of TAG and maintain the superiority in magneto-optical property.” said Jiang Li.

After considering the factors comprehensively, the research team makes the assessment. Jiang Li said, “These results demonstrate that Sc substitution brings significant benefits to the fabrication of TSAG ceramics with both high optical quality and high Verdet constant.” In the future, the research team will further reduce the optical loss coefficient and fabricate the TSAG ceramics with larger aperture and thickness.

Other contributors include Lixuan Zhang, Chen Hu, Xiao Li, Zhenzhen Zhou, Tingsong Li, Yiyang Liu, and Lexiang Wu from the Transparent Ceramics Research Center at Shanghai Institute of Ceramics, Chinese Academy of Sciences in Shanghai, China.

This work was supported by the National Key R&D Program of China (Grant No. 2023YFB3812000), the General Project of Shanghai Natural Science Foundation (Grant No. 22ZR1471500), and the Prospective Basic Research and Applied Basic Research of Hengdian Group.

See the article:

Effect of Sc substitution on the phase composition, microstructure, and properties of (Tb_1−xSc_x)₃(Al_1−ySc_y)₂Al₃O₁₂ transparent ceramics

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Journal of Advanced Ceramics (JAC) is an international academic journal that presents the state-of-the-art results of theoretical and experimental studies on the processing, structure, and properties of advanced ceramics and ceramic-based composites. JAC is Fully Open Access, monthly published by Tsinghua University Press, and exclusively available via SciOpen. JAC’s 2023 IF is 18.6, ranking in Top 1 (1/31, Q1) among all journals in “Materials Science, Ceramics” category, and its 2023 CiteScore is 21.0 (top 5%) in Scopus database. ResearchGate homepage: https://www.researchgate.net/journal/Journal-of-Advanced-Ceramics-2227-8508