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A cycle of works on manufacturing and studying laser and magnetooptical ceramics with a focus on their thermo-optical characteristics performed by the research team is analyzed. Original results that have not been published before such as measurements of the Verdet constant in the Zr:TAG, Re:MgAl2O4, and ZnAl2O4 ceramics are also presented.

A glycine-nitrate self-propagating high-temperature synthesis (SHS) was developed to produce composite MgO-Gd 2 O 3 nanopowders. The X-ray powder diffraction (XRD) analysis confirmed the SHS-product consists of cubic MgO and Gd 2 O 3 phases with nanometer crystallite size and retains this structure after annealing at temperatures up to 1200 °C. Near full dense high IR-transparent composite ceramics were fabricated by spark plasma sintering (SPS) at 1140 °C and 60 MPa. The in-line transmittance of 1 mm thick MgO-Gd 2 O 3 ceramics exceeded 70% in the range of 4–5 mm and reached a maximum of 77% at a wavelength of 5.3 mm. The measured microhardness HV0.5 of the MgO-Gd 2 O 3 ceramics is 9.5±0.4 GPa, while the fracture toughness ( K IC ) amounted to 2.0±0.5 MPa·m 1/2 . These characteristics demonstrate that obtained composite MgO-Gd 2 O 3 ceramic is a promising material for protective infra-red (IR) windows.

Nanopowders of strontium fluoroapatite Sr5(PO4)3F (SFAP) were synthesized using a co-precipitation method with different starting strontium compounds. Based on the data of XRD, BET and SEM measurements, the nitrate-derived powders were chosen as the least agglomerated. The SFAP powders were hot pressed at 1000 °C to ceramic samples with a transmittance up to 82% in a mid-IR region. The designed approach was adopted to prepare 2 mol % of Er-doped SFAP powders and ceramics. It was established that Er:SFAP ceramics have luminescence in the range of 1.5–1.7 μm, the intensity of which increases with the calcination temperature of the initial powders.

This study looked at the thermal conductivity of translucent (Y1−xGdx)2O3 (where 0 ≤ x ≤ 1) solid solution ceramics in the temperature range from 50 K to 300 K. The samples were obtained by hot pressing from high-purity nanopowders at 1600 °C, no sintering additives were used. Compositions with cubic syngony (x ≤ 0.7) and a monoclinic one (x ≥ 0.9) were investigated. Furthermore, a dense sample of cubic Gd2O3 with a LiF sintering additive was obtained and its thermal conductivity was determined (k = 11.7 W/(m K) at 300 K). It was shown that in the range of solid solution ceramic compositions 0.2 ≤ x ≤ 0.7, the thermal conductivity was practically unchanged and close to the value k ≈ 5 W/(m K) at 300 K.

Novel IR-transparent ceramics of erbium-doped Lu2O3-MgO and Sc2O3-MgO composites have been successfully obtained using a combination of glycine–nitrate self-propagating high-temperature synthesis and vacuum hot-pressing methods. Composites have densities greater than 99.5% of those calculated by X-ray diffraction and consist of uniformly distributed submicron grains of magnesium and rare earth oxides. The transmittances of 1.5 mm thick composites are as high as 84.5% and 78.9% at ~5 µm for Er:Lu2O3-MgO and Er:Sc2O3-MgO, respectively. Both composites are favorable matrices for doping with erbium ions, which exhibit intense luminescence in the visible, near, and mid-IR under relevant excitation. The position of the luminescence bands is similar to Er:Lu2O3 and Er:Sc2O3 ceramics; the lifetimes of the 4I13/2 state are 8.85 ± 0.1 ms and 5.7 ± 0.2 ms for 3%Er:Lu2O3-MgO and 3%Er:Sc2O3-MgO, respectively.

The synthesis of nanopowders of terbia compounds with scandia, yttria, and lutetia was carried out using a self-propagating high-temperature synthesis method involving a mixture of nitrates of metals and glycine as a precursor. The nanopowder phase transformations were investigated using X-ray diffraction analysis. It was found that lutetia has a negligible effect on the phase formation in terbia. On the other hand, yttrium and scandium ions significantly suppressed crystallization. The densification kinetics of nanopowders of the Tb 2 O 3 compounds and the microstructure of ceramics after microwave sintering were studied using dilatometry and scanning electron microscopy. The introduction of scandia, yttria, or lutetia contributed to the intensification of the densification of the terbia ceramics when heated in a microwave field. Near full-density materials of terbia solid solutions with lutetia and yttria were obtained at about 1600–1640 °C. The ceramics of scandia–terbia compounds contained the second phase, which causes light scattering.

(Dy0.7Y0.25La0.05)2O3 magneto-optical transparent ceramics were successfully fabricated by pressureless sintering in reductive H2 atmosphere (PLSH). The raw powder of (Dy0.7Y0.25La0.05)2O3 was synthesized by a modified self-propagating high-temperature synthesis (SHS) and sintered to transparent ceramics at 1400–1600 °C in a flowing H2 atmosphere, showing good sinterability of the as-synthesized raw powder. The magneto-optical Verdet constant of (Dy0.7Y0.25La0.05)2O3 transparent ceramics was measured to be −191.57 rad/(T·m) at a wavelength of 632.8 nm. In this magneto-optical material of (Dy0.7Y0.25La0.05)2O3, relative cheaper Dy and Y were used to replace Tb, and the low cost and good magneto-optical property showed the advantage of application on Faraday isolators (FIs) and Faraday rotators (FRs).

A glycine-nitrate self-propagating high-temperature synthesis (SHS) was developed to produce composite MgO-[Gd.sub.2][O.sub.3] nanopowders. The X-ray powder diffraction (XRD) analysis confirmed the SHS-product consists of cubic MgO and [Gd.sub.2][O.sub.3] phases with nanometer crystallite size and retains this structure after annealing at temperatures up to 1200 [degrees]C. Near full dense high IR-transparent composite ceramics were fabricated by spark plasma sintering (SPS) at 1140 C and 60 MPa. The in-line transmittance of 1 mm thick MgO-[Gd.sub.2][O.sub.3] ceramics exceeded 70% in the range of 4-5 mm and reached a maximum of 77% at a wavelength of 5.3 mm. The measured microhardness HV0.5 of the MgO-[Gd.sub.2][O.sub.3] ceramics is 9.5 [+ or -] 0.4 GPa, while the fracture toughness ([K.sub.IC]) amounted to 2.0 [+ or -] 0.5 MPa*[m.sup.1/2]. These characteristics demonstrate that obtained composite MgO-[Gd.sub.2][O.sub.3] ceramic is a promising material for protective infra-red (IR) windows. Keywords: MgO-[Gd.sub.2][O.sub.3]; self-propagating high-temperature synthesis (SHS); spark plasma sintering (SPS); optical properties; infra-red (IR) ceramics

Transparent ceramics based on ytterbium oxide have been successfully produced by vacuum sintering of self-propagating high-temperature synthesized powders with use of a La2O3 sintering aid. Phase composition and microstructure of the initial powders were studied by X-ray diffraction analysis and scanning electron microscopy. It was found that addition of 5 mol.% of La2O3 does not cause formation of secondary phases in the Yb2O3 powders. The 4% La:Yb2O3 ceramics showed the best in-line transmittance of 73% at a wavelength of 2 μm among the studied samples. Dependence of the Verdet constant on wavelength was investigated in the range of 0.4–2 μm. The most promising finding is use of the obtained material as Faraday isolators in the wavelength region of ~1.5 μm, where there are no absorption bands, and the Verdet constant is 8.6 rad/(T*m).

This study looked at optimizing the composition of precursors for yttria nanopowder glycine–nitrate self-propagating high-temperature synthesis (SHS). Based on thermodynamic studies, six different precursor compositions were selected, including with excesses of either oxidant or fuel. The powders from the precursors of all selected compositions were highly dispersed and had specific surface areas ranging from 22 to 57 m2/g. They were consolidated by hot pressing (HP) with lithium–fluoride sintering additive and subsequent hot isostatic pressing (HIP). The 1 mm thick HPed ceramics had transmittance in the range of 74.5% to 80.1% @ 1μm, which was limited by optical inhomogeneity due to incomplete evaporation of the sintering additive. Two-stage HIP significantly improves optical homogeneity of the ceramics. It was shown that an excess of oxidizer in the precursor decreases the powders’ agglomeration degree, which forms large pore clusters in the ceramics.