ZrO2-doped Y2O3 transparent ceramics via slip casting and vacuum sintering

Commercial Y₂O₃ powder was used to fabricate highly transparent Y₂O₃ ceramics with the addition of ZrO₂ via slip casting and vacuum sintering. The effects of ZrO₂ addition on the transparency, grain size and lattice parameter of Y₂O₃ ceramics were studied. With addition of ZrO₂ the transparency of Y₂O₃ ceramics increased markedly and the grain size of Y₂O₃ ceramics decreased markedly by cation diffusivity mechanism and the lattice parameter of Y₂O₃ ceramics slightly decreased. The highest transmittance (at wavelength 1100 nm) of the 5.0 mol% ZrO₂–Y₂O₃ ceramic (1.0 mm thick) sintered at 1860 °C for 8 h reached 81.7%, very close to the theoretical value of Y₂O₃.     

High optical quality Y2O3 transparent ceramics with fine grain size fabricated by low temperature air pre-sintering and post-HIP treatment

High optical quality Y₂O₃ transparent ceramics with fine grain size were successfully fabricated by air pre-sintering at various temperature ranging from 1500 to 1600 °C combined with a post-hot-isostatic pressing (HIP) treatment using co-precipitated powders as the starting material. The fully dense Y₂O₃ transparent ceramic with highest transparency was obtained by pre-sintered at 1550 °C for 4 h in air and post-HIPed at 1600 °C for 3 h (the pressure of HIP 200 MPa), and it had fine microstructure and the average grain size was 0.96 μm. In addition, the in-line transmittance of the ceramic reached 81.7% at 1064 nm (1 mm thickness). By this approach, the transparent Y₂O₃ ceramics with fine grain size (<1.6 μm) were elaborated without any sintering aid.     

Fabrication and properties of Y2O3 transparent ceramic by sintering aid combinations

Transparent Y₂O₃ ceramics were fabricated by the solid-state reaction and vacuum sintering method using La₂O₃, ZrO₂ and Al₂O₃ as sintering aids. The microstructure of the Y₂O₃ ceramics sintered from 1550 °C to 1800 °C for 8 h were analyzed by SEM. The sintering process of the Y₂O₃ transparent ceramics was optimized. The results showed that when the samples were sintered at 1800 °C for 8 h under vacuum, the average grain sizes of the ceramics were about 3.5 µm. Furthermore, the transmittance of Y₂O₃ ceramic sintered at 1800 °C for 8 h was 82.1% at the wavelength around the 1100 nm (1 mm thickness), which was close to its theoretical value. Moreover, the refractive index of the Y₂O₃ transparent ceramic in the temperature range from 30 °C to 400 °C were measured by the spectroscopic ellipsometry method.     

Fabrication and characterization of highly transparent Er:Y2O3 ceramics with ZrO2 and La2O3 additives

In this study, we report highly transparent Er:Y₂O₃ ceramics (0–10 at% Er) fabricated by a vacuum sintering method using compound sintering additives of ZrO₂ and La₂O₃. The transmittance, microstructure, thermal conductivity and mechanical properties of the Er:Y₂O₃ ceramics were evaluated. The in-line transmittance of all of the Er:Y₂O₃ ceramics (1.2 mm thick) exceeds 83% at 1100 nm and 81% at 600 nm. With an increase in the Er doping concentration from 0 to 10 at%, the average grain size, microhardness and fracture toughness remain nearly unchanged, while the thermal conductivity decreases slightly from 5.55 to 4.89 W/m K. A nearly homogeneous doping level of the laser activator Er up to 10 at% in macro-and nanoscale was measured along the radial direction from the center to the edge of a disk specimen, which is the prominent advantage of polycrystalline over single-crystal materials. Based on the finding of excellent optical and mechanical properties, the compound sintering additives of ZrO₂ and La₂O₃ are demonstrated to be effective for the fabrication of transparent Y₂O₃ ceramics. These results may provide a guideline for the application of transparent Er:Y₂O₃ laser ceramics.     

Tb3+/Yb3+ co-doped Y2O3 upconversion transparent ceramics: Fabrication and characterization for IR excited green emission

Tb³⁺/Yb³⁺ co-doped Y₂O₃ transparent ceramics were fabricated by vacuum sintering of the pellets (prepared from nanopowders by uniaxial pressing) at 1750 °C for 5 h. Zr⁴⁺ and La³⁺ ions were incorporated in Tb³⁺/Yb³⁺ co-doped Y₂O₃ nanoparticle to reduce the formation of pores which limits the transparency of ceramic. An optical transmittance of ∼80% was achieved in ∼450 to 2000 nm range for 1 mm thick pellet which is very close to the theoretical value by taking account of Fresnel’s correction. High intensity luminescence peak at 543 nm (green) was observed in these transparent ceramics under 976 and 929 nm excitations due to Yb–Tb energy transfer upconversion.     

Effects of ZrO2-La2O3 co-addition on the microstructural and optical properties of transparent Y2O3 ceramics

Commercial Y₂O₃ powder was used to fabricate Y₂O₃ ceramics sintered at 1600 °C and 1800 °C with concurrent addition of ZrO₂ and La₂O₃ as sintering aids. One group with different contents of La₂O₃ (0–10 mol%) with a fixed amount of 1 mol% ZrO₂ and another group with various contents of ZrO₂ (0–7 mol%) with a fixed amount of 10 mol% La₂O₃ were compared to investigate the effects of co-doping on the microstructural and optical properties of Y₂O₃ ceramics. At low sintering temperature of 1600 °C, the sample single doped with 10 mol% La₂O₃ exhibits much denser microstructure with a few small intragranular pores while the samples with ZrO₂ and La₂O₃ co-doping features a lot of large intergranular pores leading to lower density. When the sintering temperature increases to 1800 °C, samples using composite sintering aids exhibit finer microstructures and better optical properties than those of both ZrO₂ and La₂O₃ single-doped samples. It was proved that the grain growth suppression caused by ZrO₂ overwhelms the acceleration by La₂O₃. Meanwhile, 1 mol% ZrO₂ acts as a very important inflection point with regard to the influence of additive concentration on the transmittance, pore structure and grain size. The highest in-line transmittance of Y₂O₃ ceramic (1.2 mm in thickness) with 3 mol% of ZrO₂ and 10 mol% of La₂O₃ sintered at 1800 °C for 16 h is 81.9% at a wavelength of 1100 nm, with an average grain size of 11.2 µm.     

Transparent cubic-ZrO2 ceramics for application as optical lenses

Optical transparent polycrystalline ZrO₂ ceramics were fabricated by solid-state sintering process using first vacuum sintering followed by hot isostatic pressing. In the visible wavelength range (400–800 nm), the in-line transmittance of 5.6-mm thick samples reaches 68% at exemplary wavelength 600 nm (corresponding to an in-line absorbance based on 10 of A₁₀ = 0.08 cm^?1), which is approximately 90% of theoretical limit. The refractive indices of the ZrO₂ optoceramics at 630 nm (n_d) are varying between 2.10 and 2.20, depending on TiO₂ contents, the latter being used as sintering aid. The appearance of birefringence is strongly correlated to the addition of TiO₂ as sintering additive in the ceramic samples, whereas addition of TiO₂ and simultaneous increase in Y₂O₃ content resulted in a decrease of birefringence.     

Fabrication of transparent yttria ceramics by alcoholic slip-casting

Y₂O₃ transparent ceramics were prepared from alcoholic slurries of Y₂O₃ nanopowders via a slip-casting method to avoid the hydrolysis issue. Polyvinyl pyrrolidone (PVP), polyethylene glycol (PEG) and polyethylenimine (PEI) were used as dispersants to improve the rheological properties of the slurries. It was found that PEI is the most effective dispersant in ethanol. The adsorbed amount of PEI was evaluated by infrared absorption and rheology measurements. Y₂O₃ slurry with a solid loading of 20.8 vol% and a viscosity of <0.1 Pa s at the shear rate of 10 s⁻¹ was obtained using 1.5 wt% PEI. The slurry yielded a homogeneous green body, and finally resulted in a high-quality Y₂O₃ ceramic with the in-line transmittance of 80% at 800 nm.     

Influence of heat treatment of powder mixture on the microstructure and optical transmission of Nd:YAG transparent ceramics

Transparent Nd:YAG ceramics were fabricated by solid-state reactive sintering of Y₂O₃, α-Al₂O₃ and Nd₂O₃ powders with TEOS and MgO as sintering aids. The powders were ball-milled, dried, sieved and calcined at different temperatures. Samples sintered at 1745 °C for 10 h were utilized to observe the microstructure and the optical transmission. It is found that heat treatments of the powder mixtures above 600 °C for 1 h are necessary to remove the carbon contamination but below 800 °C for 4 h can avoid strong aggregation of the powder. So there is a room for heat-treatment, between 600 °C and 800 °C that can obtain Nd:YAG ceramics with almost pore-free microstructures and high transparency. Highly transparent Nd:YAG ceramic with 84.3% in-line transmission at 1064 nm was fabricated by sintering the 800 °C-1 h-heat-treated powder mixture at 1745 °C for 50 h. Even at wavelength of 400 nm, the transmittance of the sample reached 82.9% and the optical scattering coefficient was as low as 0.71% cm⁻¹.     

Sintering,microstructure and mechanical properties of Al2O3–Y2O3–ZrO2 (AYZ) eutectic composition ceramic microcomposites

We report on how the mechanical properties of sintered ceramics (i.e., a random mixture of equiaxed grains) with the Al₂O₃–Y₂O₃–ZrO₂ eutectic composition compare with those of rapidly or directionally solidified Al₂O₃–Y₂O₃–ZrO₂ eutectic melts. Ceramic microcomposites with the Al₂O₃–Y₂O₃–ZrO₂ eutectic composition were fabricated by sintering in air at 1400–1500 °C, or hot pressing at 1300–1400 °C. Fully dense, three phase composites of Al₂O₃, Y₂O₃-stabilized ZrO₂ and YAG with grain sizes ranging from 0.4 to 0.8 μm were obtained. The grain size of the three phases was controlled by the size of the initial powders. Annealing at 1500 °C for 96 h resulted in grain sizes of 0.5–1.8 μm. The finest scale microcomposite had a maximum hardness of 19 GPa and a four-point bend strength of 282 MPa. The fracture toughness, as determined by Vickers indentation and indented four-point bending methods, ranged from 2.3 to 4.7 MPa m^1/2. Although strengths and fracture toughnesses are lower than some directionally or rapidly solidified eutectic composites, the intergranular fracture patterns in the sintered ceramic suggest that ceramic microcomposites have the potential to be tailored to yield stronger, tougher composites that may be comparable with melt solidified eutectic composites.     

Sintering of Yb3+:Y2O3 transparent ceramics in hydrogen atmosphere

Highly transparent Yb³⁺:Y₂O₃ ceramics with doping concentration up to 40.0 at.% had been fabricated successfully via hydrogen atmosphere sintering, where the raw powders were synthesized by co-precipitation method. The sintering temperature is about 600 °C lower than its melting temperature. SEM investigation revealed the average grain size of Yb³⁺:Y₂O₃ ceramics sintered at 1850 °C for 9 h was about 7 μm. The highest transmittance of as-prepared 1 mm thickness samples around wavelength of 1050 nm reached 80%, which is close to the theoretical value of Y₂O₃. The optical spectroscopic properties of Yb³⁺:Y₂O₃ transparent ceramics have also been investigated, which shows that it is a very good laser material for diode laser pumping and short pulse mode-locked laser.     

Fabrication of LaGdZr2O7 transparent ceramic

A simple combustion method was used to synthesize LaGdZr₂O₇ powder and LaGdZr₂O₇ transparent ceramic was prepared by vacuum sintering at 1850 °C for 6 h. The final transparent ceramic, with a density of 6.46 g/cm³, has an in-line transmittance of 70.7% at 1000 nm and a refractive index of 2.08 at 632.8 nm.     

Fabrication and optical properties of Y2O3-based ceramics with broad emission bandwidth

In this article, we report on the fabrication and optical properties of highly transparent yttria ceramics for lasers active media with broadband gain profile. Laser synthesis method was used to produce Y₂O₃-based nanopowders doped with 1 mol.% Nd³⁺ or Yb³⁺ for these transparent ceramics. The additives of sesquioxides Lu₂O₃ and Sc₂O₃ were used along with ZrO₂ to disorder the crystalline structure. The porosity and average grain size decrease with these additives and the emission bandwidths of Nd³⁺ (⁴F_3/2 → ⁴I_11/2) and Yb³⁺ (²F_5/2 → ²F_7/2) transitions widen to 40 and 60 nm, respectively. Laser operation with the slope efficiency of 29% was obtained in [(Yb_0.01Lu_0.24Y_0.75)₂O₃]_0.88(ZrO₂)_0.12 ceramic sample.     

Fabrication and properties of transparent Tb:YAG fluorescent ceramics with different doping concentrations

Terbium doped yttrium aluminum garnet (Tb:YAG) transparent ceramics with different doping concentrations were fabricated by the solid-state reaction method using commercial Y₂O₃, α-Al₂O₃ and Tb₄O₇ powders as raw materials. Samples sintered at 1750 °C for 20 h were utilized to observe the optical transmittance, microstructure and fluorescence characteristics. It is found that all the Tb: YAG ceramics with different doping concentrations exhibit homogeneous structures with grain size distributions around 22–29 µm. For the 5 at% Tb:YAG transparent ceramics, the grain boundaries are clean with no secondary phases. The photoluminescence spectra show that Tb:YAG ceramics emit predominantly at 544 nm originated from the energy levels transition of ⁵D₄→⁷F₅ of Tb³⁺ ions, and the intensity of the emission peak reaches a maximum value when the Tb³⁺ concentration is 5 at%. The in-line transmittance of the 5 at% Tb:YAG ceramics is 73.4% at the wavelength of 544 nm, which needs to be further enhanced by optimizing the fabrication process. We think that Tb:YAG transparent ceramics may have potential applications in the high-power white LEDs.     

Spark plasma sintering of Sm3+ doped Y2O3 transparent ceramics for visible light lasers

Transparent Sm:Y₂O₃ ceramics were fabricated by spark plasma sintering (SPS). The effects of LiF additive and sintering temperature on the microstructure and optical transmittance of the Sm:Y₂O₃ ceramics were investigated. The optimal content of LiF additive and sintering temperature was found to be 0.3 wt% and 1500 ℃. The transmittance of Sm:Y₂O₃ ceramics with a thickness of 1.7 mm reached 75.3% at 609 nm, which is about 94% of the theoretical value. The average grain size of the sample was about 50 µm.     

Comparing the deposition mechanisms in suspension plasma spray (SPS) and solution precursor plasma spray (SPPS) deposition of yttria-stabilised zirconia (YSZ)

Thermal spraying using liquid feedstock has emerged as a promising technology for the deposition of finely structured ceramic coatings. In order to provide a comparative assessment of the deposition mechanisms occurring when spraying suspension or solution feedstock, suspensions of 300 nm-sized ZrO₂–4.5 mol.% Y₂O₃ particles dispersed in water and in ethanol and solutions of zirconium and yttrium salts, corresponding to ZrO₂–4.5 mol.% Y₂O₃ and ZrO₂–8 mol.% Y₂O₃ stoichiometries, were processed by plasma spraying using different parameter settings. In-flight diagnostics of sprayed droplets, together with the morphological, microstructural and phase analysis of individual lamellae collected onto polished substrates, performed by SEM, FIB, AFM and micro-Raman spectroscopy, led to the identification of deposition mechanisms, which were subsequently verified through the characterisation of complete coating layers.     

Mechanical and optical properties of spark plasma sintered transparent Y2O3 ceramics

Commercial Y₂O₃ nanopowder was used to fabricate transparent Y₂O₃ ceramics by spark plasma sintering under the pressure of 100 MPa for 20 min with the heating rate of 100 °C/min. The microstructures, mechanical and optical properties of the Y₂O₃ ceramics sintered at different temperatures were investigated in detail. Densification occurred up to a sintering temperature of 1500 °C, and above 1500 °C, rapid grain growth and pore growth occurred. The highest relative density of 99.58% and the minimum average grain size of 0.58±0.11 µm were obtained at 1500 °C. The flexural strength, hardness and fracture toughness of the optimal spark plasma sintered Y₂O₃ ceramic were 122 MPa, 7.60 GPa and 2.06 MPa.m^1/2, respectively. The Y₂O₃ ceramic sintered at 1500 °C had the in-line transmission of about 11–54% and 80% in the wavelength range of 400–800 nm and 3–5 µm, respectively.     

Development of ZrO2–WC composites by pulsed electric current sintering

ZrO₂–WC ceramic composites with 40 vol% WC were consolidated by pulsed electric current sintering (PECS) for 4 min at 1450 °C under a pressure of 60 MPa. The effect of ZrO₂ stabilizers and the source of WC powder on the densification, phase constitution, microstructure and mechanical properties of the ZrO₂–WC composites were investigated and analyzed. The experimental results revealed that the amount and type of ZrO₂ stabilizers played a primary role on the phase constitution and mechanical properties of the composites in comparison to the morphology and size of the WC powder. The 2 mol% Y₂O₃-stabilized composites exhibited much better mechanical properties than that of 1.75 mol% Y₂O₃-stabilized or 1 mol% Y₂O₃ + 6 or 8 mol% CeO₂ co-stabilized composites. A Vickers hardness of 16.2 GPa, fracture toughness of 6.9 MPa m^1/2, and flexural strength of 1982 MPa were obtained for the composites PECS from a mixture of nanometer sized WC and 2 mol% Y₂O₃-stabilized ZrO₂ powder.     

Hot isostatic pressing of optically active Nd:YAG powders doped by a colloidal processing route

In this work, 1 at.% Nd doped Yttrium Aluminum Garnet Y₃Al₅O₁₂ (YAG) nano-sized powder prepared by colloidal route was investigated thoroughly concerning agglomeration control and preparation of transparent ceramic by post-HIP. Electrostatic and mechanical deagglomeration process followed by freeze-drying turned out to be an effective method to alleviate agglomeration, yielding a powder with a homogeneous particle size distribution around 100 nm. Transparent Nd:YAG ceramic samples have been successfully prepared by post-HIP without the aid of sintering additives. The optical properties varied markedly with the sintering and hot isostatic pressing conditions used. In-line transmittance values of 56% at 680 nm and close to 80% in the infrared region were recorded.     

Novel amorphous precursor densification to transparent Nd:Y2O3 Ceramics

A novel approach of neodymium ion doped yttrium oxide (Nd:Y₂O₃) amorphous precursor compaction and sintering is being reported for the first time. Precursor of 2 at.% Nd³⁺ doped Y₂O₃ was synthesized by gelation of sol of yttrium and neodymium nitrates with l-alanine at 80 °C for 16 h followed by gel combustion in microwave. A part of microwave precursor was heat treated at 700 °C for 5 h to give the partially crystalline Nd:Y₂O₃ amorphous precursor. Thermogravimetric analysis (TGA) of partially crystalline amorphous precursor of Nd:Y₂O₃ gave 8.5% total weight loss indicating removal of maximum organics. X-Ray diffraction (XRD) showed broad peaks indicating incomplete crystallization of cubic Nd:Y₂O₃. Morphology was found to be close to spherical with particles in size range 17–19 nm by TEM. Another part of microwave precursor on calcination at 1000 °C for 3 h led to formation of fully crystalline Nd:Y₂O₃ with particles in size range of 35–85 nm. Both partially crystalline amorphous precursor and fully crystalline Nd:Y₂O₃ were compacted at 400 MPa by cold isostatic press and sintered at 1750 °C for 10 h under vacuum (10^?5 mbar). The partially crystalline Nd:Y₂O₃ amorphous precursor densified to 99% with 65% transmission at 2500 nm (0.5 mm thickness) compared to 96% densification with 34% transmission for fully crystalline Nd:Y₂O₃ without any sintering aids. Retention of cubic phase purity of Y₂O₃ was observed in both the ceramic pellets post sintering by XRD. Good grain fusion with grain growth to ≤2 μm was observed by scanning electron microscope (SEM) for partially crystalline Nd:Y₂O₃ amorphous precursor. Thus partially crystalline Nd:Y₂O₃ amorphous precursor nanopowders, with homogeneous close to spherical fine particles and high reactivity due to ionic mobility of amorphous phase, led to better densification.