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15LS-P-8 , ALT'22
LASER SYSTEMS AND MATERIALS
Magneto-optical and structural properties of ultrafine-grained Tb2O3
transparent ceramics
R.N. Maksimovu*, V.V. Osipov1, G.R. Karagedov3, V.V. Platonov1, A.N. Orlov1, A.V. Spirina1, A.S. Yurovskikh2, V.A. Shitov1
1Institute of Electrophysics UrB RAS, 106 Amundsen St., Ekaterinburg 620016, Russia 2Ural Federal University named after the first President of Russia B.N. Yeltsin, 19Mira St., Ekaterinburg 620002, Russia 3Institute of Solid State Chemistry andMechanochemistry SB RAS, 18 Kutateladze St., Novosibirsk 630128, Russia *email: romanmaksimov@e1.ru
Recently, ceramic materials based on terbium sesquioxide (Tb2O3) have attracted considerable interest as promising magnetically active media for Faraday isolators used in high-power solid-state lasers owing to their extremely high Ver-det constant (up to 154 radT-1 m-1 at 1064 nm) [1,2]. Transparent polycrystalline Tb2O3 ceramics offer several important advantages over their single-crystalline counterparts including enhanced optical quality and feasibility for large aperture samples [3].
Manufacturing of high performance ceramic elements is complicated by the reversible phase transformation of Tb2O3 from the cubic to the monoclinic structure above 1500°C causing fracture of sintered material. Consequently, special additives such as Y2O3 stabilizing the cubic modification and/or grain growth inhibitor (ZrO2) are used to prevent phase conversion and for achieving a pore-free microstructure. However, the thermal conductivity and Verdet constant of (TbxY1-x)2O3 solid solutions are inferior to those of "pure" Tb2O3 [3]. Tetravalent Zr doping could lead to unwanted absorption near 1 ^m and thus one of the current trends in the manufacture of sesquioxide ceramics for advanced laser applications is avoiding any kind of foreign impurities [4,5].
In this work, Tb2O3 nanoparticles with an average size of 13 nm produced by laser ablation of solid target in air flow were used to fabricate transparent ceramics without sintering additives by a combination of pressureless densification and hot isostatic press (HIP) treatment. The as-synthesized nanopowder was uniaxially dry-pressed at 50 MPa into cylindrical compacts of 14 mm diameter and then subjected to vacuum sintering for 1-2 h at 1300-1450°C followed by HIPing for 2 h at 1450°C under an Ar gas pressure of 200 MPa. The crystal structure of the obtained Tb2O3 ceramics was studied using XRD and lattice vibrational modes were analyzed by Raman and FTIR reflection spectroscopy to confirm the phase purity. According to SEM observations, the samples exhibited an ultrafine-grained and dense microstructure consisting of polyhedral-shaped crystallites of less than 1 ^m in size. The distribution of scattering centers throughout the depth of the samples was obtained using an optical microscope and its correlation with transmission spectra registered over the wavelength range 200-1100 nm was investigated. The Verdet constant of the fabricated Tb2O3 ceramics was measured at 632.8 nm and 1064 nm using He-Ne and Nd:YAG lasers, respectively. For instance, the Verdet constant at 632.8 nm was evaluated to be at least 478 radT-1m-1, which is comparable to that of high purity Tb2O3 single-crystal grown by the flux method (476 radT-1m-1) [6]. Thus, the highly sinterable nanopowders produced by laser ablation could be promising for the fabrication of transparent Tb2O3 ceramics without sintering additives.
The reported study was carried out with the use of grant № 22-23-00658 of the Russian Science Foundation, https:// rscf.ru/en/project/22-23-00658/
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