钇铝石榴石(YAG)激光透明陶瓷研究进展

钇铝石榴石(YAG)激光透明陶瓷由于具有单晶、玻璃激光材料无可比拟的优势而成为研究热点,并得到迅速发展,高性能的稀土元素掺杂YAG透明激光陶瓷被相继报导.本文综述了近年来国内外关于YAG激光透明陶瓷的最新研究成果.主要包括YAG微细粉体合成、烧结添加刺及多晶YAG透明陶瓷的致密化烧结技术,并对比了YAG透明陶瓷相对于Y...     

Grain Boundary Grooving Studies of Yttrium Aluminum Garnet (YAG) Bicrystals

Grain boundary grooving experiments were conducted with Σ5 (210) twist boundaries in Y₃Al₅O₁₂ (YAG) with the goal of extracting information on diffusion in YAG. Planar boundaries oriented 90° to the surface were annealed in air at various times and temperatures. Atomic force microscopy was used to characterize the subsequent grooves. The Mullins approach leads to the following expression for the diffusion coefficient: D (m²/s) = 3.9 × 10⁻¹⁰ exp[−330 ± 75 (kJ/mol)/ RT ]. The relatively low activation energy agrees well with earlier oxygen tracer diffusion measurements on YAG, suggesting that oxygen is the limiting diffusing species in boundary grooving of YAG.     

Low-Temperature Fabrication of Transparent Yttrium Aluminum Garnet (YAG) Ceramics without Additives

A carbonate precursor of yttrium aluminum garnet (YAG) with an approximate composition of NH₄AlY_0.6(CO₃)_1.9(OH)₂·0.9H₂O was synthesized via a coprecipitation method from a mixed solution of ammonium aluminum sulfate and yttrium nitrate, using ammonium hydrogen carbonate as the precipitant. The precursor precipitate was characterized using chemical analysis, differential thermal analysis/thermogravimetry, X-ray diffractometry, and scanning electron microscopy. The sinterability of the YAG powders was evaluated by sintering at a constant rate of heating in air and vacuum sintering. The results showed that the precursor completely transforms to YAG at ∼1000°C via the formation of a yttrium aluminate perovskite (YAP) phase. YAG powders obtained by calcining the precursor at temperatures of ≤1200°C were highly sinterable and could be densified to transparency under vacuum at 1700°C in 1 h without additives.     

Yttrium Aluminum Garnet (YAG) Films through a Precursor Plasma Spraying Technique

Coatings of yttrium aluminum garnet (Y₃Al₅O₁₂, YAG), which is a promising high-temperature ceramic, were developed for the first time using a novel precursor plasma spraying (PPS) technique. The precursor sol was sprayed using a radio-frequency induction plasma technique. X-ray diffraction analysis of the as-sprayed coatings confirmed that a metastable hexagonal yttrium aluminate (H-YAlO₃) was the major phase. The above-described specimen, on further treatment with plasma, was converted to cubic garnet (YAG) as the major phase, with a minor amount of orthorhombic YAlO₃ (O-YAP) phase. ²⁷Al magic-angle spinning nuclear magnetic resonance of the YAG coating corroborated the X-ray results and confirmed the presence of YAG and O-YAP phases. Formation of the garnet phase through the PPS technique is proof that the chemistry can be controlled in the plasma. This finding opens up new avenues for developing complex functional oxide deposits.     

热处理温度对钇铝石榴石(Y3Al5O12)析晶的影响

透明YAG多晶陶瓷具有优良的光学、机械与化学性能,逐渐成为新一代固体激光基质材料.分散均匀、团聚轻、超细颗粒的纳米前驱体粉末有利于制备出高度透明的激光陶瓷.以Y2O3,Al(NO3)3·9H2O和柠檬酸为原料,采用柠檬酸-凝胶法和低温自蔓延燃烧反应相结合制备出黑色粉末,经1100℃烧结出YAG纳米前驱体粉末.采用TG-DTA,XRD,FT-IR和TEM测试手段对YAG前驱体粉末进行表征,采用谢莱公式计算出不同烧结温度下晶粒尺寸.研究结果表明:随热处理温度升高,晶粒平均尺寸增加,标准偏差以小幅度增加,晶粒尺寸分布曲线保持一致,晶格参数减小.随热处理时间增加,晶粒主要以晶界扩散形式线性长大.纳米晶粒表面原子呈不规则分布,导致晶格参数增加,前驱体颗粒由单个晶粒所构成.     

Ytterbium Cation Diffusion in Yttrium Aluminum Garnet (YAG)—Implications for Creep Mechanisms

The lattice and grain-boundary diffusion coefficients of ytterbium, which substitutes for yttrium, have been determined in high-purity, stoichiometric yttrium aluminum garnet (YAG) polycrystals in the temperature range 1400°–1550°C, in air. Ytterbium oxide thin films were produced on the YAG surfaces by a dipping method. After diffusion treatments, the penetration profiles were established by secondary ion mass spectroscopy, and the diffusion coefficients were calculated from the thin-film solution of Fick's equation. The difference between the volume and grain-boundary diffusion coefficients is ∼5 orders of magnitude in the temperature range studied. The cation activation energies (∼550 kJ/mol) are much larger than those for oxygen (∼300–350 kJ/mol). The effective diffusion coefficient deduced from high-temperature deformation data reported in the literature for YAG polycrystals, assuming grain-boundary sliding accommodated by volume diffusion, is in excellent agreement, both in magnitude and activation energy, with the cation diffusion data.     

The Influence of Cation Additives on Grain‐Boundary Mobility in Yttrium Aluminum Garnet (YAG)

Pure yttrium aluminum garnet (YAG) nano‐powders, doped with 1.4 at.% of La₂O₃, ZrO₂, MgO, Nb₂O₅, and SiO_2, were vacuum sintered to full density and subjected to grain growth at 1700°C, for up to 15 h. The YAG intrinsic grain‐boundary (GB) mobility, determined from the pure fully dense YAG specimens, was 2.9 × 10^?16 [m³·N^?1·s^?1]. All dopants, except for La₂O₃, increased the GB mobility compared to pure YAG (La₂O₃ didn't cause any significant change in YAG's GB mobility). All GBs were found to be free of secondary phases or intergranular films. These findings differ from numerous publications where dopants were found to either inhibit grain growth by solute drag, or to enhance grain growth due to liquid phase sintering. It was found that the GB mobility systematically increased with the decrease in the dopant cation radius. Moreover, it seems that vacancy population plays an important role in determining the GB mobility of YAG.     

软机械力化学辅助固相法合成铈掺杂钇铝石榴石荧光粉及其发光性能

采用机械研磨方法(振动磨和介质搅拌磨)对混合原料(氧化钇、氧化铝、氧化铈、氯化铵和氟化钡粉末)进行软机械力化学预处理,获得前驱体,利用高温固相法合成铈掺杂钇铝石榴石(YAG:Ce3+)荧光粉。借助X射线衍射、扫描电子显微镜和激光粒度分析仪,分析了YAG:Ce3+荧光粉的物相、显微结构和粒度分布。结果表明:混合原料经软机械力化学方法预处理后,后续高温固相法合成温度可降低300℃。相对于振动磨,采用介质搅拌磨进行软机械力化学预处理,可使前驱体的颗粒细度减小,晶格缺陷增多,非晶化程度增加。对于氧化钇(222)晶面,介质搅拌磨处理后,结晶度可降低至45.7%,而振动磨处理后晶度降低至73.02%,介质搅拌磨机械力化学处理,可使后续合成过程中粉体反应活性增加。在较低合成温度(1 300℃)烧成,经软机械力化学预处理前驱体粉体的合成晶相为完整而无杂相的YAG晶相,并可在蓝光激发下发出黄光。此种合成的荧光粉可应用于白光发光二极管。     

Segregation in Yttrium Aluminum Garnet: II, Theoretical Calculations

Calculations based on ionic space-charge models of doped yttrium aluminum garnet (YAG) have been compared to experimental measurements of surface segregation in crystals of various compositions. The comparison allows limits for vacancy-formation energies to be set. The range for anion:cation formation-energy ratios has been established to be 0.20-0.23, based on the reasonable assumptions that the formation energy of the yttrium ion is 75% of that of the aluminum ion and the Schottky defect formation energy is 4.2 eV. The model explains the experimental observation of calcium at the surface regardless of net acceptor excess or net donor excess. The relationship between vacancy-formation energy and dopant excess has been used to construct segregation maps for YAG, which are useful in materials design strategies.     

Segregation in Yttrium Aluminum Garnet: I, Experimental Determination

Single crystals of yttrium aluminum garnet (YAG) that were doped with various cations were annealed in air at different temperatures for varying amounts of time. Dopants were chosen to probe the effect of size, charge, and site occupancy on surface segregation. Of the dopants that were chosen for the study (calcium, silicon, neodymium, chromium, and strontium), calcium was the only one that consistently segregated upon annealing in air. Calcium enrichment to the (111) surface was measured using Auger electron spectroscopy, and the segregation enthalpy was determined to be δ H _seg≈−32 ± 10 kJ/mol. Enrichment occurred according to variations in valence, as opposed to variations in size; therefore, it is suggested that surface segregation is electrostatically driven. The results indicate that aliovalent substituents could be used for interface property tailoring, whereas isovalent dopants would not be useful.     

Microstructure Development in Yttrium Iron Garnet

Sintering and grain-growth rates were determined for yttrium iron garnet as a function of the yttrium/iron ratio. Rates decreased with an increase in this ratio; this behavior is interpreted as a result of the oxygen content variation through the garnet field. For constant sintering time, density and grain size, as well as microstructure-dependent properties, varied through the garnet field. Remanent magnetization and coercive force in particular depended on composition and sintering temperature. The rf field for nonlinear spin-wave excitation, h _crit, measured for dense samples with grain sizes from ∼4 to 30 μm, varied by a factor of four.     

Spherical Yttrium Aluminum Garnet Embedded in a Glass Matrix

Containerless processing was used to investigate the glass-forming behavior of Al₂O₃–Y₂O₃ glass. The amorphous bulk samples were obtained at compositions with 25–37.5 mol% yttria when the melt was cooled at a cooling rate of ∼250 K/s. Although small spherical particles (∼10 μm) with the same composition of the matrix were detected in the amorphous samples with 32.5–37.5 mol% yttria, the microfocus X-ray diffraction result indicated that the small spherical particles were crystalline Y₃Al₅O₁₂ garnet (YAG), rather than being amorphous. This observation suggested that small YAG particles could not grow larger after their nucleation, because of the high viscosity at high undercooling and the high cooling rate, which would graze the nose of the continuous cooling temperature diagram of YAG.     

Eutectic Precipitation of the Spinel Solid Solution-Yttrium Aluminum Garnet (YAG) System

Isothermally solidified microstructures of the alumina-rich spinel solid solution—yttrium aluminum garnet (YAG) composite was investigated. It was identified that the eutectic phase relation of the YAG—spinel system could be maintained with the formation of an alumina-rich spinel solid solution, despite the significant change in eutectic compositions. In addition, divorced eutectic precipitates that have a spinel-rich composition were observed surrounding the YAG dendrites.     

Microstructural Development and Creep Deformation in an Alumina–5% Yttrium Aluminum Garnet Composite

An alumina–5 vol% yttrium aluminum garnet (YAG) composite was obtained through in situ reaction of alumina and yttria during sintering. Analysis of creep experiments together with microstructural data indicated that both pure alumina and alumina–5 vol% YAG composite deform by a Coble grain boundary diffusion creep process. Comparison with other data suggests that at temperatures greater than ∼1650 K, an isolated or interconnected fine-grained YAG phase does not significantly affect creep in alumina. However, an isolated YAG phase retards both static and dynamic grain growth in the composite.     

Effect of Composition on the Oxygen Tracer Diffusion in Transparent Yttrium Aluminium Garnet (YAG) Ceramics

The grain boundary structure and oxygen tracer diffusion in transparent yttrium aluminum garnet (YAG) ceramics varying from 2% excess of Y₂O₃ to 0.5% excess of Al₂O₃ were studied. The characterization of the specimens is as follows: (i) For the Y₂O₃-excess specimen, a second phase (yttrium aluminum perovskite: YAP) containing silicon in the grain boundary was found, (ii) For the Al₂O₃-excess specimen, both aluminum-rich particles (alumina) and a silicon-rich segregant layer were observed in the grain boundary. The volume diffusion of the oxygen tracer is little influenced by the excess composition. In contrast, the grain boundary diffusion of the oxygen tracer is suppressed in the Y₂O₃-excess specimens, compared to Al₂O₃-excess specimens. These differences are thought to result from the chemical reaction between the second phase and the intergranular liquid phase during the sintering.     

钇铝石榴石纤维的制备和应用研究进展

钇铝石榴石纤维具有耐高温、抗氧化、低导热率、优异的抗高温蠕变性和良好的光学性能,是一种理想的结构增强材料、绝热耐火材料和光学材料.本文重点评述了近年来钇铝石榴石纤维制备和应用的研究进展,并展望了钇铝石榴石纤维制备和应用的发展趋势.     

Undercooled Melt Formation and Shaping of Alumina–Yttrium Aluminum Garnet Eutectic Ceramics

Undercooled melt was produced in the alumina-rich portion of the Al₂O₃–Y₂O₃ system, heating the metastable eutectic structure to above the metastable eutectic temperature but below the equilibrium eutectic temperature, followed immediately by solidification along the equilibrium path in the undercooled melt. Coupling the melting and solidification enabled a nearly adiabatic transformation from the metastable eutectic structure to the equilibrium eutectic structure. The eutectic structure produced through the solidification was uniform and fine throughout the castings. A fin-type casting with a thickness of 300 μm was successfully produced. This paper proposes a novel casting process using the undercooled melt formation.