Fabrication of 4 at.% La3+ ion doped (TbxLu0.96−x)2O3 transparent ceramics by using NC-PLSH technology and characterisation of their magneto-optical properties

Nanocrystalline powders and pressureless sintering (NC-PLSH) were used in a H₂ atmosphere to fabricate 4 at.% La³⁺ doped (Tb_xLu_0.96?x)₂O₃ magneto-optical transparent ceramics. La³⁺ was utilised as a sintering aid, and Lu³⁺ was used as a phase stabiliser. A component of the (Tb_xLu_0.96?xLa_0.04)₂O₃ magneto-optical material was designed and investigated based on powder sinterability and green compact sintering. Transparent (Tb_xLu_0.96?xLa_0.04)₂O₃ ceramics were obtained by using a one-step sintering process in H₂ atmosphere, without the need for subsequent hot isostatic pressing. The in-line transmittance of the as-polished 4 at.% La³⁺:(Tb_0.8Lu_0.16)₂O₃ ceramic was 79% at 1400 nm. The measured Verdet constant at wavelengths of 633 nm and 1064 nm was 354 rad/(T·m) and 100.2 rad/(T·m), respectively. The required length of the (Tb_0.8Lu_0.16La_0.04)₂O₃ ceramics was 63% less than that of Tb₃Ga₅O₁₂ ceramics.     

Fabrication and properties of transparent Tb2Ti2O7 magneto-optical ceramics

Transparent Tb₂Ti₂O₇ magneto-optical ceramics were fabricated from co-precipitated nano-powders by vacuum pre-sintering with hot isostatic pressing (HIP) post-treatment. The formation of pyrochlore phase, decomposition of the precursor, and the morphology of powders calcined at different temperatures were investigated. The in-line transmittance of Tb₂Ti₂O₇ ceramics, which were pre-sintered at 1350 ℃ for 2 h with HIP post-treatment at 1450 ℃ for 3 h and subsequently annealed at 800 ℃ for 20 h in NH₃ atmosphere, reaches 65.5 % at 1064 nm. The Verdet constant of Tb₂Ti₂O₇ ceramics is −229.0 ± 0.6 rad·T⁻¹ m⁻¹ at the wavelength of 633 nm, which is 71 % higher than that of the commercial Tb₃Ga₅O₁₂ crystals. Tb₂Ti₂O₇ magneto-optical ceramics show a promising application for Faraday rotators.     

Fabrication and characterizations of Tb3Al5O12-based magneto-optical ceramics

Transparent terbium aluminum garnet (TAG)-based ceramics were fabricated by vacuum pre-sintering and hot isostatic pressing (HIP) posttreatment from the co-precipitated TAG powders with different stoichiometric ratios. After component optimization, the transparent ceramics with TAG single-phase and attractive optical quality were obtained. The in-line transmittance of optimal Tb_(1+x)3(Al_0.996255Si_0.003745)₅O_{12.0093625+3x/2} (x = −.004, −.002) ceramics (1.7-mm thick) pre-sintered at 1700°C for 20 h with HIP posttreatment at 1700°C for 3 h under 176-MPa Ar reaches 82.6% at the wavelength of 1064 nm. With increasing terbium components, the secondary phase TAP appears in ceramics, which significantly degrades the optical quality of TAG-based ceramics. The Verdet constant of the TAG-based ceramics at 632.8 nm is about −181 rad T⁻¹ m⁻¹ at room temperature, which is about 33% higher than that of the TGG single crystals (−134 rad T⁻¹ m⁻¹).     

Development of optical grade (TbxY1−x)3Al5O12 ceramics as Faraday rotator material

Super full dense (Tb_xY_1?x)₃Al₅O₁₂ (x=0.5‐1.0) ceramics with optical grade (pore‐free) were successfully produced by solid‐state reaction between Tb₄O₇ and Al₂O₃ raw powders. Transparent sintered bodies were obtained by sintering at 1720°C for 5 hours in vacuum furnace. By additional HIP treatment, optical scattering centers were effectively removed, and finally the optical quality of the sintered bodies was improved to optical grade. Optical loss of the obtained samples at 1064 nm was approximately 0.1%/cm, and optically inhomogeneous parts were not observed inside the materials. Gaussian mode laser beam quality was not deteriorated after passing through the sample. Transmitted wavefront distortion inspected by interferometry was as excellent as λ/12. Verdet constant increased with an increase of Tb content in the garnet composition. When x=1.0, the Verdet constant was 307, 196, and 60 rad T^?1 m^?1 for 532, 633, and 1064 nm, respectively, at each measuring wavelength. These values were about 1.5 times higher than that of the commercially available TGG (Tb₃Ga₃O₁₂) crystal. Insertion loss of the produced (Tb_0.6Y_0.4)₃Al₅O₁₂ and TAG ceramics at 1064 nm was 0.01 and 0.05 dB, respectively, and extinction ratio was 39.5 and 40.3 dB, respectively. These properties were superior to that of the commercial high‐quality TGG single crystal (insertion loss: 0.05 dB, extinction ratio: 35.0 dB).     

Photoluminescence and unique magnetoluminescence of transparent (Tb1-xYx)3Al5O12 ceramics

Luminescent transparent ceramics (Tb_1-xY_x)₃Al₅O₁₂ (x = 0, 0.2, 0.5, 0.8) are successfully prepared by a solid-state method with additional hot isostatic pressing (HIP) treatment, and the structure and properties are investigated by XRD, SEM, PL, UV–Vis spectrophotometry and ellipsometry. The Y-containing samples are shown to be solid solution phases between TAG and YAG. The PL intensity is 14 times stronger with the incorporation of 80 mol.% Y, and the ⁵D₄→⁷F₅ emission lifetime of Tb³⁺ is prolonged from 0.357 to 3.035 ms at room temperature. A unique magnetoluminescence emerges upon the incorporation of Y, showing an interesting emission decrease to 55% as the Y content reaches 80 mol.%. Remarkably, this magnetoluminesence can occur at room temperature without an intense magnetic field. Based on our work, transparent (Tb_1-xY_x)₃Al₅O₁₂ ceramics exhibit the potential for applications in green emitters, optical instruments and photoelectric devices. In particular, the magnetoluminescence provides a simple, noncontact and nondestructive route for probing magnetic fields.     

Magneto-optical,thermal, and mechanical properties of polycrystalline Tb3Al5O12 transparent ceramics

Terbium aluminum garnet (Tb₃Al₅O₁₂, TAG) ceramics have become a promising magneto-optical material owing to the outstanding comprehensive performance, including the magneto-optical, thermal, and mechanical properties. Fine-grained TAG ceramics with high optical quality and mechanical properties have attracted much attention. In this study, TAG ceramics with fine grains and high optical quality are fabricated successfully by a two-step sintering method from co-precipitated nano-powders. After pre-sintered at 1525°C in vacuum and hot isostatic pressed at 1600°C, the in-line transmittance of TAG ceramics reaches 81.8% at 1064 nm, and the average grain size is 7.1 μm. The Verdet constant of TAG ceramics is −179.6 ± 4.8 rad T⁻¹ m⁻¹ at 633 nm and −52.1 ± 1.9 rad T⁻¹ m⁻¹ at 1064 nm, higher than that of commercial Tb₃Ga₅O₁₂ crystals. The thermal conductivity of TAG ceramics is determined from 25 to 450°C, and the result is 5.12 W m⁻¹ K⁻¹ at 25°C and 3.61 W m⁻¹ K⁻¹ at 450°C. A comparison of mechanical properties between large- and fine-grained TAG ceramics fabricated under different conditions is conducted. The fine-grained TAG ceramics possess a bending strength of 226.3 ± 16.4 MPa, which is 9.7% higher than that of the large-grained ceramics. These results indicate that reducing the grain size on the premise of high optical quality helps improve the comprehensive performance of TAG ceramics.     

Broadening emission band of Yb:LuScO3 transparent ceramics for ultrashort pulse laser

Sesquioxides were considered as promising gain medium for high power ultrafast laser. Broadening of emission spectrum plays a crucial role in shortening the pulse width of laser. In this paper, the ratio of lutetium oxide and scandium oxide was adjusted to control the emission wavelength and spectral width. Highly sinterable Yb:(Lu_xSc_1–x)₂O₃ nanopowders were synthesized through the glycine-nitrate combustion process. Transparent Yb:(Lu_xSc_1–x)₂O₃ ceramics were fabricated via vacuum sintering at 1750℃ for 10 h, among which Yb:(Lu_0.5Sc_0.5)₂O₃ ceramics have the highest transmittance, reaching 78% at 1100 nm. With increasing Lu₂O₃ content, the emission wavelengths corresponding to the two transitions of Yb:(Lu_xSc_1–x)₂O₃ were blueshifted 8 and 15 nm, respectively. Most importantly, from Yb:Sc₂O₃ to Yb:(Lu_0.5Sc_0.5)₂O₃, spectral broadening of the two emission wavelengths was observed by 9 and 16 nm, respectively. Thus, the Yb:(Lu_xSc_1-x)₂O₃ ceramics exhibiting high transmittance and broad emission band are promising for ultrashort pulse generation.     

Sintering parameter optimization of Tb3Al5O12 magneto-optical ceramics by vacuum sintering and HIP post-treatment

Transparent terbium aluminum garnet (TAG) ceramics were achieved by the vacuum sintering plus HIP post-treating from the coprecipitated TAG nanoparticles. The influences of vacuum sintering temperature and sintering aid TEOS on the optical quality of the TAG ceramics were studied. The results show that with the increase of sintering temperature, the optical quality of TAG ceramics is improved gradually, and the in-line transmittance of the TAG ceramics treated at 1720°C for 20 hours under vacuum and then HIP post-treated at 1700°C for 3 hours under 200 MPa argon gas is 81.6% at 1064 nm. The sintering additive TEOS can improve the optical quality of TAG ceramics and inhibit the valence state change of Tb³⁺ ions to Tb⁴⁺ during the annealing process. The Verdet constant of the TAG ceramics at 632.8 nm is about −178 rad·T⁻¹·m⁻¹ at room temperature, which is 1.3 times that of the commercial TGG crystals (−134 rad·T⁻¹·m⁻¹).     

Effect of La2O3 on the microstructure and optical performance of (Tb0.8Y0.2-xLax)2O3 ceramics

(Tb_0.8Y_0.2-xLa_x)₂O₃ transparent ceramics were prepared by using co-precipitation method combined with pressure-less sintering in flowing H₂ atmosphere. Microstructure, optical transmittance, elements composition, and Verdet constant of the (Tb_0.8Y_0.2-xLa_x)₂O₃ ceramics were studied. The amount of La₂O₃ is crucial for the formation of expected transparent (Tb_0.8Y_0.2)₂O₃. With increasing content of La₂O₃, the number of pores and the grain size of as-fabricated (Tb_0.8Y_0.2-xLa_x)₂O₃ ceramics both decrease. When 4 at.% La₂O₃ is doped, the (Tb_0.8Y_0.16)₂O₃ transparent ceramics shows the highest transmittance of 73.3% at 1400 nm wavelength. With holding time increasing from 8 h to 15 h, the average grain size of (Tb_0.8Y_0.16La_0.04)₂O₃ ceramics gradually increases from 5 μm to 13 μm. The Verdet constant measured at 633 nm is ?352 rad/T·m, which is 2.63 times higher than that of TGG. In addition, large-size ceramics with Φ 20 mm × 3 mm and Φ 30 mm × 3 mm were also successfully obtained.     

Fabrication,microstructure and spectroscopic properties of Yb:Lu2O3 transparent ceramics from co-precipitated nanopowders

Ytterbium doped lutetium oxide (Yb:Lu₂O₃) transparent ceramics were fabricated by vacuum sintering combined with hot isostatic pressing (HIP) of the powders synthesized by the co-precipitation method. The effects of calcination temperature on the composition and morphology of the powders were investigated. Fine and well dispersed 5?at% Yb:Lu₂O₃ powders with the mean particle size of 67?nm were obtained when calcined at 1100?°C for 4?h. Using the synthesized powders as starting material, we fabricated 5?at% Yb:Lu₂O₃ ceramics by pre-sintering at different temperatures combined with HIP post-treatment. The influence of pre-sintering temperature on the densities, microstructures and optical quality of the 5?at% Yb:Lu₂O₃ ceramics was studied. The ceramic sample pre-sintered at 1500?°C for 2?h with HIP post-treating at 1700?°C for 8?h has the highest in-line transmittance of 78.2% at 1100?nm and the average grain size of 2.6?µm. In addition, the absorption and emission cross sections of the 5?at% Yb:Lu₂O₃ ceramics were also calculated.     

Fabrication and magneto-optical property of yttria stabilized Tb2O3 transparent ceramics

(Tb_0.5Y_0.5)₂O₃ transparent ceramics have been prepared by wet chemical co-precipitation route and flowing H₂ atmosphere sintering. The optical quality, microstructure and magneto-optical properties of the ceramics were investigated. No sintering aids or milling were adopted in the ceramic fabrication processing. The cold isostatic pressed green compact could be sintered to be transparent (Tb_0.5Y_0.5)₂O₃ ceramic at 1800 ℃ in flowing H₂ atmosphere. The mechanical polished ceramic showed the good transmittance from visible to near infrared wavelength, corresponding to a 71.9% transmittance at 1400 nm wavelength. The Verdet constant measured at 632.8 nm of the (Tb_0.5Y_0.5)₂O₃ transparent ceramics was -220.19 rad T⁻¹ m^-1, which was 1.64 times that of Tb₃Ga₅O₁₂ single crystal.     

Fabrication of transparent Tb3Al5O12 ceramics by hot isostatic pressing sintering

Tb₃Al₅O₁₂ (TAG) transparent ceramics were prepared by a reactive sintering method using presintering in a muffle furnace combined with hot isostatic pressing (HIP) sintering. The dilatometric, differential scanning calorimetry‐thermogravimetric (DSC‐TG) curves and optical quality were investigated. The microstructure evolution of the TAG ceramic samples was clarified. Two successive transformations were found to generate a TAG phase, as observed in the dilatometric and DSC‐TG curves and XRD patterns of TAG ceramics sintered at different temperature. The changes in average grain size and densification suggest that a 1600°C presintering temperature is suitable for HIP. The optical transmittance of the obtained 0.4 wt% TEOS:TAG transparent ceramics, which were fabricated by a new two‐step sintering of presintering at 1600°C in a muffle furnace followed by HIP at 1650°C, can reach above 80% in the visible (vis) and near‐infrared (NIR) regions. Its transmittance was very close to the theoretical limit. To the best of our knowledge, this is the first time that TAG transparent ceramics with ideal optical quality were obtained without vacuum sintering.     

Effect of Y doping on microstructure and thermophysical properties of yttria stabilized hafnia ceramics

A series of Y₂O₃-doped HfO₂ ceramics (Hf_1-xY_xO_2-0.5×, x?=?0, 0.04, 0.08, 0.12, 0.16 and 0.2) were synthesized by solid-state reaction at 1600?°C. The microstructure, thermophysical properties and phase stability were investigated. Hf_1-xY_xO_2–0.5x ceramics were comprised of monoclinic (M) phase and cubic (C) phase when Y³⁺ ion concentration ranged from 0.04 to 0.16. The thermal conductivity of Hf_1-xY_xO_2–0.5x ceramic decreased as Y³⁺ ion concentration increased and Hf_0.8Y_0.2O_1.9 ceramic revealed the lowest thermal conductivity of ~?1.8?W/m*K at 1200?°C. The average thermal expansion coefficient (TEC) of Hf_1-xY_xO_2–0.5x between 200?°C and 1300?°C increased with the Y³⁺ ion concentration. Hf_0.8Y_0.2O_1.9 yielded the highest TEC of ~?10.4?×?10^?6 K^?1 while keeping good phase stability between room temperature and 1600?°C.     

The role of 4f14 Lu3+ and 3d0 Sc3+ in faraday rotating glass/ceramic: Structural stability,magnetic and magneto optical properties

Magneto-optical materials exhibiting low/no temperature-dependent Faraday rotation, high magnetization and good thermal/mechanical stability are required in various magneto-optical sensing and photonic applications. For the first time, we employed the rare earth Lu³⁺ and Sc³⁺ ions to strengthen the structure and enhance magnetic& magneto-optical properties of heavy metal oxide diamagnetic glasses. Experimental results revealed that the doping of Lu₂O₃ and Sc₂O₃ not only significantly increased the UV-VIS transmittance, improved the thermal stability, Vicker's hardness and tensile strength, but also remarkably increased the magnetic susceptibility and Verdet constant. The reasons were analyzed through the XRD, FT-IR, Raman spectra, oxygen chemical bonds, EPR of Lu₂O₃ and Sc₂O₃ crystal fields and affinity to oxygen. Promising Faraday rotating glass with Verdet constant of 76.32 rad/Tm at 633 nm, thermal stability KH = 0.817, very low thermal expansion coefficient (14.04 × 10^?6 K^?1) and high diamagnetic susceptibility of 9.25 × 10^?6 emu/g has obtained which has potential merits for photonics and MO devices applications.     

Effects of Yb and Sc co-doping on the thermal properties and CMAS corrosion of garnet-type (Y3-xYbx)(Al5-xScx)O12 ceramics

Thermal barrier coatings with excellent thermal performance and corrosion resistance are essential for improving the performance of aero-engines. In this paper, (Y_3-xYb_x)(Al_5-xSc_x)O₁₂ (x = 0, 0.1, 0.2, 0.3) thermal barrier coating materials were synthesized by a combination of sol-gel method and ball milling refinement method. The thermal properties of the (Y_3-xYb_x)(Al_5-xSc_x)O₁₂ ceramics were significantly improved by increasing Yb and Sc doping content. Among designed ceramics, (Y_2.8Yb_0.2)(Al_4.8Sc_0.2)O₁₂ (YS-YAG) showed the lowest thermal conductivity (1.58 Wm^?1K^?1, at 800 °C) and the highest thermal expansion coefficient (10.7 × 10^?6 K^?1, at 1000 °C). In addition, calcium-magnesium- aluminum -silicate (CMAS) corrosion resistance of YS-YAG was further investigated. It was observed that YS-YAG ceramic effectively prevented CMAS corrosion due to its chemical inertness to CMAS as well as its unique and complex structure. Due to the excellent thermal properties and CMAS corrosion resistance, YS-YAG is considered to be prospective material for thermal barrier coatings.     

Fabrication of Yb-doped Lu2O3-Y2O3-La2O3 solid solutions transparent ceramics by self-propagating high-temperature synthesis and vacuum sintering

A comparative analysis of sintering and grain growth processes of lutetium oxide and lutetium-yttrium-lanthanum oxides solid solutions, as well as optical properties, luminescence and laser generation of (Lu_xY_0.9-xLa_0.05Yb_0.05)₂O₃ transparent ceramics are reported. Fabrication of highly dispersed initial powders of these compounds was performed via nitrate-glycine self-propagating high-temperature synthesis (SHS) method. The powders were compacted at 300?MPa and vacuum sintered at temperatures up to 1750?°С. Optical ceramics of (Lu_0.65Y_0.25La_0.05Yb_0.05)₂O₃ elemental composition were shown to have the highest in-line transmittance, which achieved 78% at the wavelength of 800?nm. Generation of laser radiation at a wavelength of 1032?nm with the differential efficiency of 20% was demonstrated in the (Lu_0.65Y_0.25La_0.05Yb_0.05)₂O₃ ceramics.     

Fantastic valence impacts of Pr on microstructures and Faraday magneto-optical effects of transparent (Ho,Pr)2O3 ceramics

Polycrystalline magneto-optical (Ho_1-xPr_x)₂O₃ (x = 0.05?0.2) ceramics were fabricated by vacuum sintering using layered rare-earth hydroxides as the precursors, among which the 5 at.% Pr doped specimen exhibits the highest in-line transmittance of ～76.1 % at 700 nm (～94.5 % of the theoretical value of defect-free Ho₂O₃ single crystal) and the largest Verdet constant of ?82 ± 6 rad?T^?1 m^?1 at 1064 nm (～2.3 times that of the commercial Tb₃Ga₅O₁₂ crystal and ～1.8 times that of the pure Ho₂O₃ ceramic). More Pr addition not only leads to a higher thermal decomposition temperature for the precursor but also a decreasing particle size for the oxide. A 5 at.% Pr dopant in Ho₂O₃ matrix generally exists in the oxidation state of +3, while an increasing Pr concentration up to 10 at.% induces coexisting valences of +3 and +4. The grain growth was suppressed by the present Pr⁴⁺ based on interstitial mechanism. The substitution of Pr³⁺ for Ho³⁺ is helpful for the rising Verdet constant of the binary ceramic, but Pr⁴⁺ has little positive contribution to it.     

Structure and thermal properties of Al2O3-doped Gd3TaO7 as potential thermal barrier coating

In this paper, a series of solid solutions ceramics of (Al_xGd_1-x)₃TaO₇ (x = 0, 0.01, 0.03, 0.05) were synthesized via solid-state reaction. X-ray diffraction (XRD) and Raman spectroscopy analysis indicated that the crystal structure of (Al_xGd_1-x)₃TaO₇ ceramics is weberite in spite of the content of Al³⁺ is up to 5 mol.%. The thermal conductivities of (Al_xGd_1-x)₃TaO₇ ceramics range from 1.37 W?m^?1 K^?1 to 1.47 W?m^?1 K^?1 at 900 ℃, which is much lower than that of 7–8 YSZ (about 2.5 W?m^?1 K^?1). The thermal expansion coefficients (TECs) of (Al_xGd_1-x)₃TaO₇ ceramics vary in the range of 6–10 × 10^-6 K^-1 within the temperature range 100–1200 ℃, and the values are close to the TECs of 7–8 YSZ. Given the low thermal conductivity and high thermal expansion coefficients of (Al_xGd_1-x)₃TaO₇ ceramics, they have the potential to be the next generational thermal barrier coating materials.     

Fabrication and laser operation of Yb:Lu2O3 transparent ceramics from co-precipitated nano-powders

In this article, 5 at.% Yb:Lu₂O₃ transparent ceramics were fabricated by vacuum sintering combined with hot isostatic pressing (HIP) posttreatment using co-precipitated nano-powders. The influence of precipitant molar ratio, ammonium hydrogen carbonate, to metal ions (AHC/M³⁺, R value) on the properties of Yb:Lu₂O₃ precursors and calcined powders was investigated systematically. It was found that the powders with different R value calcined at 1100°C for 4 hours were pure cubic Lu₂O₃ but the morphologies of precursors and powders behaved differently. The opaque samples pre-sintered at 1500°C for 2 hours grew into transparent ceramics after HIP posttreatment at 1750°C for 1 hour. The final ceramic with R = 4.8 showed the best optical quality with the in-line transmittance of 79.7% at 1100 nm. The quasi-CW laser operation was performed at 1034 nm and 1080 nm with a maximum output power up to 8.15 W as well as a corresponding slope efficiency of 58.4%.     

Enhanced negative thermal expansion of (KMg)3+-substituted Fe2Mo3O12 ceramics

Herein, we report the solid-state synthesis of (KMg)_xFe_2-xMo₃O₁₂ (0 = x ≤ 1.5) ceramics. Phase composition, crystal structure, morphology, phase transition and thermal expansion behavior of the (KMg)_xFe_2-xMo₃O₁₂ ceramics were investigated by XRD, Raman, XPS, HRTEM, EDX, SEM, TMA and high-temperature XRD. Results indicate that (KMg)³⁺ dual-cations have successfully replaced Fe³⁺ in Fe₂Mo₃O₁₂ ceramics and single-phase monoclinic (KMg)_xFe_2-xMo₃O₁₂ ceramics were prepared for 0.25 = x ≤ 1. (KMg)³⁺ introduction can increase the density of (KMg)_xFe_2-xMo₃O₁₂ ceramics and effectively improve their negative thermal expansion (NTE) performance. In addition, the phase transition temperature (Tc) of Fe₂Mo₃O₁₂ was reduced from 508.1 °C to room temperature with the increase of (KMg)³⁺-substitution. Monoclinic KMgFeMo₃O₁₂ ceramics was observed to show stronger NTE in a wider temperature range of 30–700 °C for the first time. Its corresponding coefficient of thermal expansion (CTE) is as high as ?17.21 × 10^?6 °C^?1. The distortion of [FeO₆/MgO₆] polyhedra in (KMg)_xFe_2-xMo₃O₁₂ caused by (KMg)³⁺-substitution contributed to the stronger NTE.