Flame-Sprayed Y<Subscript>2</Subscript>O<Subscript>3</Subscript> Films with Metal-EDTA Complex Using Various Cooling Agents

In this study, yttrium oxide (Y₂O₃) films were synthesized from a metal-ethylenediaminetetraacetic (metal-EDTA) complex by employing a H₂-O₂ combustion flame. A rotation apparatus and various cooling agents (compressed air, liquid nitrogen, and atomized purified water) were used during the synthesis to control the thermal history during film deposition. An EDTA·Y·H complex was prepared and used as the staring material for the synthesis of Y₂O₃ films with a flame-spraying apparatus. Although thermally extreme environments were employed during the synthesis, all of the obtained Y₂O₃ films showed only a few cracks and minor peeling in their microstructures. For instance, the Y₂O₃ film synthesized using the rotation apparatus with water atomization units exhibited a porosity of 22.8%. The maximum film’s temperature after deposition was 453 °C owing to the high heat of evaporation of water. Cooling effects of substrate by various cooling units for solidification was dominated to heat of vaporization, not to unit’s temperatures.     

Effects of rare earth oxide additives on the thermal behaviors of aluminum nitride ceramics

The effects of Y₂O₃ and Er₂O₃ on the sintering behaviors, thermal properties and microstructure of AlN ceramics were investigated. The experimental results show that the sintering temperature can be decreased; the relative density and thermal behavior can be improved by adding rare earth oxide in AlN ceramics. For AlN ceramics with 3 wt.% Er₂O₃ additive, the relative density is 98.8%, and the thermal conductivity reaches 106 W·m⁻¹·K⁻¹. The microstructure research found that no obvious aluminum erbium oxide was found in AlN ceramics doped with 3 wt.% Er₂O₃, which favored the improvement of the thermal conductivity of AlN ceramics.     

Single-Step Synthesis of Cubic Y<Subscript>2</Subscript>O<Subscript>3</Subscript>:Eu<Superscript>3+</Superscript> Nanophosphor by Flame Spray Pyrolysis

In this report, we investigated a single-step process for formation of high crystallinity Y₂O₃:Eu³⁺ red nanophosphor by flame spray pyrolysis (FSP) without post-heat treatments. Crystallinity of as-formed nanophosphor particle was improved by addition of urea to the nitrate-based liquid precursor. Urea increased the temperature in the flame zone thus ensuring Y₂O₃:Eu³⁺ formation at higher flame temperature. Higher temperature reached during combustion of urea promoted the formation of better crystallinity, nano-sized and spherical-shaped particles. The effect of urea in the precursor to obtain high-efficiency Y₂O₃:Eu³⁺ nanophosphor was studied.     

Enhancement of upconversion luminescence of Y2O3:Er nanocrystals by codoping Li-Zn

The upconversion (UC) luminescence in sol-gel synthesized Li⁺, Zn²⁺, or Li⁺-Zn²⁺ codoped Y₂O₃:Er³⁺ nanocrystals were investigated under the excitation of a 970 nm diode laser. Compared to undoped Y₂O₃:Er³⁺ samples, proper doping of Li⁺-Zn²⁺ leads to an drastic increase of the UC luminescence centered at 560 nm by a factor of 28. The UC luminescence enhancement is a result of the increased lifetime of the intermediate state ⁴I_11/2 (Er). The intensity ratio of the green over red emissions (green/red) is also affected by the codoping of Zn²⁺, Li⁺ and Li⁺-Zn²⁺ ions. Our results demonstrated that the Li⁺-Zn²⁺ codoping in Y₂O₃:Er³⁺ phosphors produced remarkable enhancement of the UC luminescence and green/red ratio, making this nanocrystal a promising candidate for photonic and biological applications.     

High luminance YAG:Ce nanoparticles fabricated from urea added aqueous precursor by flame process

High luminance Y₃Al₅O₁₂:Ce³⁺ (YAG:Ce) nanoparticles were prepared from urea-added nitrate aqueous precursor by flame-assisted spray pyrolysis (FASP). The addition of urea into nitrate precursor plays an important role in YAG:Ce nanoparticle formation and in improving its optical performance. The decomposition and combustion of urea in the flame zone provides additional heat to the particles, which coupled with the evolution of large volumes of gasses, contributes to nanoparticle formation. The as-prepared nanoparticles are hexagonal YAlO₃, that are nearly spherical, rough on the surface and dense—and they can be converted to YAG:Ce after being annealed at 1200 °C for 4 h. The heat-treated particles are single crystalline, smooth in surface and dense with an average size around 50 nm. The optimum cerium-doping concentration of YAG:Ce nanoparticles is 4.0 at.%, which exhibits quantum efficiency of 45.0%. This quantum efficiency is comparable with that of YAG:Ce nanoparticles produced from other processes. The efficient emission of YAG:Ce nanoparticles also originates from a relatively good distribution of Ce ions incorporated into the host material of YAG as evidenced from the elemental mapping analysis.     

Mechanical properties of Mo-Si-B alloys fabricated by using core-shell powder with dispersion of yttria nanoparticles

In recent years, refractory materials with excellent high-temperature properties have been in the spotlight as a next generation’s high-temperature materials. Among these, Mo-Si-B alloys composed of two intermetallic compound phases (Mo₅SiB₂ and Mo₃Si) and a ductile α-Mo phase have shown an outstanding thermal properties. However, due to the brittleness of the intermetallic compound phases, Mo-Si-B alloys were restricted to apply for the structural materials. So, to enhance the mechanical properties of Mo-Si-B alloys, many efforts to add rare-earth oxide particles in the Mo-Si-B alloy were performed to induce the improvement of strength and fracture toughness. In this study, to investigate the effect of adding nano-sized Y₂O₃ particles in Mo-Si-B alloy, a core-shell powder consisting of intermetallic compound phases as the core and nano-sized α-Mo and Y₂O₃ particles surrounding the core was fabricated. Then pressureless sintering was carried out at 1400 °C for 3 h, and the mechanical properties of sintered bodies with different amounts of Y₂O₃ particles were evaluated by Vickers hardness and 3-point bending test. Vickers hardness was improved by dispersed Y₂O₃ particles in the Mo-Si-B alloy. Especially, Mo-3Si-1B-1.5Y₂O₃ alloy had the highest value, 589 Hv. The fracture toughness was measured using Mo-3Si-1B-1.5Y₂O₃ alloy and the value indicated as 13.5 MPa·√m.     

Spectroscopy features of Pr and Er ions in Li2O-ZrO2-SiO2 glass matrices mixed with some sesquioxides

The glasses of the composition Li₂O-ZrO₂-SiO₂: Pr₂O₃/Er₂O₃ mixed with three interesting sesquioxides (viz., Al₂O₃, Sc₂O₃, Y₂O₃) were synthesized. Optical absorption and fluorescence spectra (in the spectral range 350-2100 nm were studied at ambient temperature. The Judd-Ofelt theory was applied to characterize the absorption and luminescence spectra of Pr³⁺ and Er³⁺ ions in these glasses. Following the luminescence spectra, various radiative properties like transition probability A, branching ratio β and the radiative life time τ for different emission levels of two rare earth ions have been evaluated. The radiative life times for the upper levels ³P₀ (Pr³⁺) and ⁴S_3/2 (Er³⁺) have also been measured and quantum efficiencies were estimated. The variations observed in these parameters were discussed in the light of changing environment of rare earth ions due to mixing of different sesquioxides in the glass network.     

Preparation and optical properties of Y<Subscript>2</Subscript>O<Subscript>3</Subscript>/SiO<Subscript>2</Subscript> powder

Y(NO3)3 and NH3·H2O were used as a raw materials,and nano-Y2O3 powder was successfully synthesized by a precipitation method.Employing TEOS as a raw material,SiO2 powder was successfully prepared by a alkoxide-hydrolysis method,and a Y2O3/SiO2 composite powder was obtained by coating.The Y2O3,SiO2,and Y2O3/SiO2 powders were characterized using X-ray diffraction(XRD),scanning electron microscopy(SEM),and Fourier transform infrared spectrophotometer(FT-IR);the Y2O3 and Y2O3/SiO2 powders were further examined ...     

Effects of shape and size of second phase on mechanical properties of sintered Mo-Y2O3 alloys

The morphology and size of second phase greatly influence the strengthening effect on oxidation dispersion strengthened Mo alloys. In this work, a novel nanostructuring strategy is adopted to modify the second phase of Y₂O₃, and the corresponding effects of particle shape and size on mechanical properties of sintered Mo-Y₂O₃ alloys were investigated. It is found that spherical particles with sizes below 200 nm are preferred due to the dominant intragranular distribution of second phases associated with better strengthening effect originating from dislocation pinning. With smaller particle size of Y₂O₃ nanospheres (105 nm), the tensile strength of corresponding Mo alloy is enhanced by about 43.8%, much higher than that (8.3%) reinforced by second phase nanospheres with larger particle size (322 nm). Meanwhile, with similar particle size (around 100 nm), the spherical shape exhibits better strengthening effect than the one reinforced by one-dimensional rod-like second phase.     

Effect of MoSi2/rare earth composite particles on microstructure and mechanical properties of molybdenum

MoSi₂/La₂O₃ and MoSi₂/Y₂O₃ composite particles were prepared by mechanical milling and doped into molybdenum by solid-solid method, respectively. Rods with a diameter of 17 mm were made by pressing and sintering. The effects of different composite particles on microstructures and strength of the as-sintered molybdenum were investigated. Results show that the MoSi₂/La₂O₃ and MoSi₂/Y₂O₃ composite particles transformed to La₂O₃/Mo₅Si₃ and Y₂O₃/Mo₅Si₃ composite particles due to the in situ reaction between Mo and MoSi₂ during sintering process. Mo₅Si₃/La₂O₃ and Mo₅Si₃/Y₂O₃ composite particles can reduce the grain size and improve both strength and toughness of sintered molybdenum significantly. Mo₅Si₃/Y₂O₃ composite particles contribute more to the strength, while the effect of Mo₅Si₃/La₂O₃ on toughness is greater than that of Mo₅Si₃/Y₂O₃.     

Effects of chromium doping on performance of LiNi0.5Mn1.5O4 cathode material

In order to improve the cycle and rate performance of LiNi_0.5Mn_1.5O₄, LiCr_2YNi_0.5–YMn_1.5–YO₄ (0≤Y≤0.15) particles were synthesized by the sucrose-aided combustion method. The effects of Cr doping in LiNi_0.5Mn_1.5O₄ on the structures and electrochemical properties were investigated. The samples were characterized by X-ray diffractometry (XRD), scanning electron microscopy (SEM), cyclic voltammetry (CV), galvanostatic charge-discharge test and electrochemical impedance spectrum (EIS). The results indicate that the LiCr_2YNi_0.5–YMn_1.5–YO₄ possess a spinel structure and small particle size, and LiCr_0.2Ni_0.4Mn_1.4O₄ exhibits the best cyclic and rate performance. It can deliver discharge capacities of 143 and 104 mA·h/g at 1C and 10C, respectively, with good capacity retention of 96.5% at 1C after 50 cycles.     

Spectra and energy levels of Er3+ in Er2O3 powder

The emission and absorption spectra of Er³⁺ ions in Er₂O₃ powder are investigated at room temperature. The crystal field splitting of ⁴I_15/2, ⁴I_13/2, ⁴I_9/2 and ⁴S_3/2 multiplets of Er³⁺ was calculated using a parameterized Hamiltonian including crystal field terms. A final standard deviation of 5.3 cm⁻¹ is obtained between 22 calculated and experimental Stark. The strength crystal field parameters of Er₂O₃ powder are compared to those of erbium doped Y₂O₃ single crystal. In addition, the location of the ground and the first excited states of Er³⁺ in Er₂O₃ powder is determined. The ⁴I_15/2 ground state of Er³⁺ is located at 12750 cm⁻¹ below the valence band edge. The ⁴I_13/2 and ⁴I_11/2 multiplets are set in resonance with the valence band. A configuration coordinate diagram is proposed for Er³⁺ in Er₂O₃ powder.     

Plasma Sprayed Dense MgO-Y2O3 Nanocomposite Coatings Using Sol-Gel Combustion Synthesized Powder

MgO-Y₂O₃ nanostructured composite powder (volume ratio of 50:50) was synthesized by a sol-gel combustion process which generated crystal sizes in the 10-20 nm range. The MgO-Y₂O₃ nanopowder was plasma sprayed using a conventional, DC arc plasma spray system. X-ray diffraction analysis shows that the as-sprayed MgO-Y₂O₃ coating is composed of cubic MgO and Y₂O₃ phases and has ~95% density. Microstructure characterization by SEM reveals that the as-sprayed coating has fine grain sizes of 100-300 nm as a result of rapid solidification. The hardness of the coating, 7.5 ± 0.6 GPa, is higher than that of coarse-grained, dense MgO, and Y₂O₃ ceramics. This approach demonstrates the potential of plasma spray processes for making thick, dense MgO-Y₂O₃ nanocomposite performs for applications as durable, infrared windows.     

Effect of Y2O3 crucible on contamination of directionally solidified intermetallic Ti–46Al–8Nb alloy

The effect of Y₂O₃ crucible on contamination of Ti–46Al–8Nb (at.%) alloy directionally solidified (DS) in a Bridgman-type apparatus was studied. Directional solidification experiments were performed in dense Y₂O₃ crucibles using different growth rates, melt temperatures and various reaction time between the melt and the crucible. The main mechanism responsible for the contamination of the DS samples is diffusion controlled dissolution of the Y₂O₃ crucible in the melt which leads to an increase of oxygen and yttrium content in γ(TiAl) + α₂(Ti₃Al) matrix and precipitation of non-metallic particles in interdendritic region. Transmission electron microscopy (TEM), energy-dispersive spectroscopy (EDS) and X-ray diffraction analysis (XRD) showed that these particles are Y₂O₃ phase. The oxygen content and volume fraction of Y₂O₃ particles increase with increasing melt temperature and reaction time. The activation energy for increase of oxygen content is calculated to be Q_O = 412.1 kJ/mol and the kinetics of this process is suggested to be controlled by long-range diffusion with the oxygen content exponent of 3. The activation energy for Y₂O₃ particle formation is calculated to be Q_Y = 421.8 kJ/mol and the time exponent is determined to be m = 0.55. Vickers microhardness measurements in lamellar γ + α₂ matrix without Y₂O₃ particles can be used as an indirect evidence of the level of contamination of DS samples with statistically identical α₂–α₂ interlamellar spacing.     

Synthesis and characteristics of W–Ti alloy dispersed with Y2Ti2O7 oxides

Tungsten based ODS alloys are the focus of attention in developing plasma-facing materials for future fusion devices. The stable Y₂Ti₂O₇ dispersed oxide phase has recently attracted considerable interest due to good lattice coherence with the matrix and refinement of the oxide particles. In this present work, the Y₂Ti₂O₇ oxide phase has been successfully synthesized. New W–Ti model alloys with different amounts of the dispersed oxide particles fabricated by mechanical alloying were investigated. The effect of Y₂Ti₂O₇ on the microstructure and mechanical properties of the model alloys has been examined. The results show that an appropriate amount of Y₂Ti₂O₇ in the tungsten matrix exhibits homogeneous microstructure with a uniform distribution of Ti-rich oxide particles, resulting in an increase in hardness and elastic modulus of the alloys. Oxidation of the materials and formation of complex Ti–Y–O oxides during ball milling and sintering are also discussed.     

Effects of Bi doping on the optical properties of Er:Y2O3

The influences of Bi³⁺ doping on the optical properties of Er³⁺:Y₂O₃ are investigated under UV and IR excitations. The emission intensity of Er³⁺ is remarkably enhanced by the introduction of Bi³⁺ under both two excitations. The emission enhancement under UV excitation originates from the energy transfer from Bi³⁺ to Er³⁺, while under IR excitation it can be attributed to the modification of the local crystal field around the Er³⁺.     

New ternary Yb5Sb3-type R5PtX2 compounds (R = Y,Gd and Er; X = Sb and Bi) and their magnetic properties

Six novel Yb₅Sb₃-type compounds (space group Pnma) have been synthesized: Y₅PtSb₂, Gd₅PtSb₂, Er₅PtSb₂, Y₅PtBi₂, Gd₅PtBi₂ and Er₅PtBi₂. The Gd₅PtSb₂, Gd₅PtBi₂, Er₅PtSb₂ and Er₅PtBi₂ undergo a ferromagnetic-type ordering followed by lower-temperature field sensitive magnetic transitions.     

Upconversion luminescence in Er/Yb codoped Y2CaGe4O12

Calcium yttrium tetrametagermanates Y₂CaGe₄O₁₂ doped with Er³⁺ and Er³⁺/Yb³⁺ reveal upconversion emission in visible spectral range under near-infrared excitation, λ_ex = 980 nm. For the solid solution Er_xY_2−xCaGe₄O₁₂ concentration dependencies for the green and red lines of the visible emission around 526 nm (²H_11/2 → ⁴I_15/2), 545 nm (⁴S_3/2 → ⁴I_15/2) and 670 nm (⁴F_9/2 → ⁴I_15/2) show the optimal value for the sample x = 0.2. The power dependence of the visible luminescence measured at room temperature in the low-power limit indicates two-photon upconversion process. Direct intensification of the upconversion emission signals has been achieved by ytterbium sensitizing. The other upconversion excitation mechanism in Y₂CaGe₄O₁₂:Er³⁺ is discussed for an 808 nm incident laser irradiation. A scheme of excitation and emission routes involving ground/excited state absorption, energy transfer upconversion, nonradiative multiphonon relaxation processes in trivalent lanthanide ions in Y₂CaGe₄O₁₂:Er³⁺ and Y₂CaGe₄O₁₂:Er³⁺, Yb³⁺ has been proposed. Conditions for visible emission occurrence under quasi-resonance λ_ex = 1064 nm excitation depending on pump power values are considered. In the low-power regime only near-infrared emission caused by the transition ⁴I_13/2 → ⁴I_15/2 in erbium ions has been detected.     

Preparation of Al2O3–ZrO2–Y2O3 Composite Coatings by a Modified Sol–Gel Technique for Thermal Barrier Application

Spatial-network Al₂O₃–ZrO₂–Y₂O₃ composite coatings were prepared by a modified sol–gel technique, so-called thermal pressure and filtration of sol–gel paint. The composite coatings were derived from a composite paint of yttria partially stabilized zirconia (YSZ) particles, Al₂O₃ particles and Al₂O₃–Y₂O₃ sol. Their microstructure showed that YSZ particles were covered with spatial-network Al₂O₃–Y₂O₃ blanket. Cyclic oxidation at 1,050 °C in air for 200 h demonstrates that the oxygen diffusion rate in the coatings could be effectively inhibited. Meanwhile, suitable coefficients of thermal expansion (CTE) gave the composite coatings better spallation resistance than that of Al₂O₃–Y₂O₃ or ZrO₂–Y₂O₃ coatings. The positive results of cyclic oxidation indicated that the composite coating can be used as an interlayer between the bond coat and the top ceramic layer in traditional TBCs. Not only the depletion rate of aluminum-rich phase in MCrAlY alloy could be slowed down by spatial-network Al₂O₃–Y₂O₃, but also different thermal expansion between thermally grown oxides layer and top layer could be relieved by suitable CTE. In this paper, the mechanisms of the inhibition of oxygen diffusion and thermal match between ceramic coating and alloy are also discussed.     

Isothermal section of the Co-Er-Y ternary system at 500 °C

The isothermal section of the phase diagram of the Co-Er-Y ternary system at 500 °C was investigated by X-ray powder diffraction technique, differential thermal analysis, scanning electron microscopy with energy dispersive analysis and optical microscopy. The 500 °C isothermal section consists of 14 single-phase regions, 19 two-phase regions, and 6 three-phase regions. Six pairs of corresponding compounds Er₂Co₁₇ and Y₂Co₁₇, Er₂Co₇ and Y₂Co₇, ErCo₃ and YCo₃, ErCo₂ and YCo₂, Er₄Co₃ and Y₄Co₃, Er₃Co and Y₃Co and metals Y and Er form a continuous series of solid solutions. The maximum solid solubility of Y in the compounds Er₁₂Co₇ is about 19 at.% Y.