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1.
Ivar E. Reimanis M. E. Hawley T. E. Mitchell D. S. Zhou 《Journal of the American Ceramic Society》1995,78(8):2282-2286
The fracture surfaces of single-crystal Y3 A15 O12 (YAG) have been examined in detail using differential interference microscopy and atomic force microscopy. In YAG crystals grown in 1977 by the Czochralski method strikingly regular undulations of microscopic and submicroscopic dimensions (4–20 nm in amplitude, 1–20 μm in wavelength) are observed on every fracture surface. The undulations do not exhibit typical characteristics of Wallner lines; furthermore, they are not observed in identical fracture tests for YAG crystals grown in 1990 by the Czochralski method. Transmission electron microscopy reveals that the crystals grown in 1977 exhibit a periodic fluctuation of the ratio of the concentrations of aluminum to yttrium, suggesting that the fracture surface features are caused by periodic astoichiometry. 相似文献
2.
Yong S. Cho Vernon L. Burdick Vasantha R. W. Amarakoon 《Journal of the American Ceramic Society》1997,80(6):1605-1608
The influences of processing parameters such as mineralizer, temperature, and nonstoichiometry on reaction product and morphology were investigated in the hydrothermal synthesis of yttrium iron garnet, Y3 Fe5 O12 (YIG). A cubic YIG phase was synthesized successfully under hydrothermal conditions of 200°C and 6 h from yttrium and iron hydroxide coprecipitates obtained by adjusting the pH to 10.5 using NH4 OH. The other mineralizer, NaOH, was not effective in forming the garnet phase. Nonstoichiometric compositions utilizing excess Y content tended to increase the yield of the garnet phase, but did not affect the morphology. Different morphology characteristics were observed by changing the synthesis temperature. Isometric YIG particles disappeared at a relatively high temperature of 250°C, resulting in irregular star-shaped particles of YIG due to the preferential orientation during particle growth. 相似文献
3.
Kentaro Fukuda Teiichi Hanada Setsuhisa Tanabe Takeshi Yao 《Journal of the American Ceramic Society》2002,85(4):915-920
Amorphous films in the system Al2 O3 –Y2 O3 were prepared by the rf sputtering method in the range of 0–76 mol% Y2 O3 , and their density, refractive index, and elastic constants were measured. All of the physical properties of the amorphous Al2 O3 –Y2 O3 films had a similar compositional dependence; that is, they increased continuously, but not linearly with increasing Y2 O3 content. To confirm the coordination states of aluminum and yttrium ions in the amorphous Al2 O3 –Y2 O3 films, the Al K α X-ray emission spectra and the X-ray absorption near edge structures (XANES) were measured. The average coordination number of aluminum ions in the amorphous films containing up to about 40 mol% Y2 O3 content was 5, that is a mixture of 4-fold- and 6-fold-coordinated states. In the region of more than about 50 mol% Y2 O3 , the fraction of the 6-fold-coordinated aluminum ions increased with increasing Y2 O3 content, while the results led to the conclusion that the coordination number of yttrium ions was always 6, regardless of composition. These results indicate that, in amorphous films in the system Al2 O3 –Y2 O3 , the change of the coordination state of aluminum ions has an important effect on physical properties. 相似文献
4.
A novel and cost-effective electrostatic spray-assisted vapor deposition (ESAVD) was used to deposit Y3 Al5 O12 (YAG) coatings. Polycrystalline single-phase Y3 Al5 O12 coatings were synthesized using the ESAVD method in an open atmosphere at 650°C, and then annealed at 700°–900°C for 1 h. The ESAVD process involves the decomposition and chemical reactions of charged aerosol in vapor phase. The low-temperature coating deposition characteristics of the ESAVD process using a suitable sol precursor decreases the reaction and crystallization temperatures for forming Y3 Al5 O12 coatings. The microstructure of the Y3 Al5 O12 coating prepared using the ESAVD method is columnar and such strain-resistance microstructure could be useful for thermal barrier coating applications. 相似文献
5.
Joanna McKittrick Carlos F. Bacalski G. A. Hirata Kevin M. Hubbard S. G. Pattillo Kenneth V. Salazar M. Trkula 《Journal of the American Ceramic Society》2000,83(5):1241-1246
The purpose of this study was to identify and correlate the microstructural and luminescence properties of europium-doped Y2 O3 (Y1– x Eu x )2 O3 thin films deposited by metallorganic chemical vapor deposition (MOCVD), as a function of deposition time and temperature. The influence of deposition parameters on the crystallite size and microstructural morphology were examined, as well as the influence of these parameters on the photoluminescence emission spectra. (Y1– x Eu x )2 O3 thin films were deposited onto (111) silicon and (001) sapphire substrates by MOCVD. The films were grown by reacting yttrium and europium tris(2,2,6,6-tetramethyl–3,5-heptanedionate) precursors with an oxygen atmosphere at low pressures (5 torr (1.7 × 103 Pa)) and low substrate temperatures (500°–700°C). The films deposited at 500°C were smooth and composed of nanocrystalline regions of cubic Y2 O3 , grown in a textured [100] or [110] orientation to the substrate surface. Films deposited at 600°C developed, with increasing deposition time, from a flat, nanocrystalline morphology into a platelike growth morphology with [111] orientation. Monoclinic (Y1– x Eu x )2 O3 was observed in the photoluminescence emission spectra for all deposition temperatures. The increase in photoluminescence emission intensity with increasing postdeposition annealing temperature was attributed to the surface/grain boundary area-reduction effect. 相似文献
6.
Phase relations of the system Fe2 O3 -Y2 O3 -Al2 O3 were studied at 1500° and 1525°C in air and in oxygen at 1 atm. Isothermal-isobaric sections indicate that the liquids phase field at 1500°C is larger in oxygen than in air. In either atmosphere, at this temperature, the composition of the garnet phase in equilibrium with a liquid is enriched in aluminum relative to the liquid. In the same manner, yttrium orthoferrite is enriched in aluminum relative to garnet in equilibrium between these two phases. The limit of solid solubility of excess iron-aluminum and/or yttrium in the garnet phase Y3 Fe4 AlO12 was determined by X-ray diffraction techniques to be 0.2 ± 0.05 mole % Y2 .O3. 相似文献
7.
Monika Agarwal Mark R. de Guire Arthur H. Heuer 《Journal of the American Ceramic Society》1997,80(12):2967-2981
Undoped or Y2 O3 -doped ZrO2 thin films were deposited on self-assembled monolayers (SAMs) with either sulfonate or methyl terminal functionalities on single-crystal silicon substrates. The undoped films were formed by enhanced hydrolysis of zirconium sulfate (Zr(SO4 )·4H4 O) solutions in the presence of HCl at 70°C. Typically, these films were a mixture of two phases: nanocrystalline tetragonal- ( t -) ZrO2 and an amorphous basic zirconium sulfate. However, films with little or no amorphous material could be produced. The mechanism of film formation and the growth kinetics have been explained through a coagulation model involving homogeneous nucleation, particle adhesion, and aggregation onto the substrate. Annealing of these films at 500°C led to complete crystallization to t -ZrO2 . Amorphous Y2 O3 -containing ZrO2 films were prepared from a precursor solution containing zirconium sulfate, yttrium sulfate (Y2 (SO4 )3 8·H2 O), and urea (NH2 CONH2 ) at pH 2.2–3.0 at 80°C. These films also were fully crystalline after annealing at 500°C. 相似文献
8.
Tai-Il Mah Kristin A. Keller Sankar Sambasivan Ronald J. Kerans 《Journal of the American Ceramic Society》1997,80(4):874-878
Heat treatments in several environments were performed on a series of compounds in the Al2 O3 and Y2 O3 system: Al2 O3 Y3 Al5 O12 eutectic, Y3 Al5 O12 , YAlO3 , Y4 Al2 O9 , and Y2 O3 . The yttrium aluminates were found to be stable at high temperatures under vacuum and in air. However, when they were heat-treated under vacuum in proximity to SiC, degradation was observed. This was found to be primarily a result of carbothermal reduction. In a similarly reducing environment without Si, the yttrium aluminates, and Al2 O3 and Y2 O3 , all exhibited degradation by carbothermal reduction. Based upon the experimental results, a degradation mechanism for yttrium aluminates was proposed. 相似文献
9.
The electrical conductivities of single crystal and polycrystalline MgAl2 O4 and Y3 Al5 O12 were measured to 1260 K using a three-contact, guard-ring technique. The electrical conduction mechanisms change with temperature, with anomalous oxygen pressure and time-dependent inflections in log σ versus T−1 curves between 900 to 1000 K. The conduction processes of Y3 Al5 O12 and MgAl2 O4 appear to be similar and possibly related to A13+ ion diffusion. 相似文献
10.
Measurements were made of temperature and ternary composition for coexisting liquid and crystalline phases on the air isobar in the system Fe2 O3 -Fe3 O4 -YFeO3 with particular regard to the stability range and compositional limits of yttrium iron garnet. Phase equilibrium relations were determined by conventional quenching techniques combined with measurements of loss in weight at the reaction temperature to locate true ternary compositions. The intersection of the air isobar with the ternary univariant boundary curve for coexisting magnetite, garnet, and liquid phases results in a eutectic-type situation at the composition Y0.27 Fe1.73 O2.87 and 1469°± 2°C. A similar intersection of the isobar with the boundary curve for coexisting garnet, orthoferrite, and liquid phases gives rise to a peritectic-type reaction at 1555° 3°C. and Y0.44 Fe1.56 O2.89 The yttrium iron garnet crystallizing from liquids within these temperature and composition limits contains up to 0.5 mole % iron oxide in excess of the stoichiometric formula in terms of the starting composition 37.5 mole % Y2 O3 , 62.5 mole % Fe2 O3 . At 1470° C. the garnet phase in equilibrium with oxide liquid contains 2 mole % FeO in solid solution. The small solubility of excess of iron oxide and partial reduction of the garnet phase in air are unavoidable during equilibrium growth from the melt. 相似文献
11.
Guo-Jun Zhang Hideki Kita Naoki Kondo Tatsuki Ohji 《Journal of the American Ceramic Society》2005,88(8):2246-2248
The effect of Y2 O3 addition (0–5 wt%) on the densification and properties of reactive hot-pressed alumina (Al2 O3 )–boron nitride composites based on the reaction between aluminum borate (2Al2 O3 ·B2 O3 ) and aluminum nitride (AlN) was investigated. The densification process was very sensitive to the amount of Y2 O3 . Compared with a low relative density of 79.3 theoretical density (TD)% for material with no Y2 O3 addition, the material density reached 98.6 TD% with 0.25% Y2 O3 addition. High Y2 O3 additions resulted in the formation of a new phase Al5 Y3 O12 . The grain growth of the Al2 O3 matrix was promoted by the Y2 O3 addition. Owing to the high density and the small Al2 O3 particle size the sample with 0.25% Y2 O3 addition demonstrated the highest bending strength of 540 MPa. 相似文献
12.
Nallusamy Venkatachalam Yu Saito Kohei Soga 《Journal of the American Ceramic Society》2009,92(5):1006-1010
The synthesis and characterization of yttrium hydroxyl carbonate (Y(OH)CO3 2− ) and yttrium nitrate hydroxide hydrate (Y(OH)NO3 H2 O) precursor materials as well as Y2 O3 nanoparticles are reported. The resultant precursor particle size is about 10–12 nm with a narrow size distribution by the enzymatic decomposition method, whereas the particle size was smaller than those acquired by the homogeneous and alkali precipitation methods. The formation of Y(OH)CO3 2− and Y(OH)NO3 H2 O species was also evident from the fourier-transform infrared spectrometry (FT-IR) analysis. Precipitated Y(OH)CO3 2− precursors have an amorphous nature whereas Y(OH)NO3 H2 O precursors have a crystalline nature, which was manifested from the XRD analysis. Moreover, precipitated Y(OH)NO3 H2 O precursors were found in the agglomerated form and Y(OH)CO3 2− was established in the monodispersed form, as determined from the FE-SEM, TEM and DLS measurements. It was demonstrated that calcination of precursor materials at 900°C eventually removed the inorganic anions from the precursors and consequently produced crystalline Y2 O3 nanoparticles, which was evident from the XRD and FT-IR analysis. The EDS analysis confirms Er3+ doping in the Y2 O3 nanoparticles. The morphology and the size of the Y2 O3 nanoparticles are almost unchanged before and after the calcination. 相似文献
13.
Mark I. Jones Hideki Hyuga Kiyoshi Hirao Yukihiko Yamauchi 《Journal of the American Ceramic Society》2004,87(4):710-713
α-SiAlONs with equiaxed and elongated microstructures stabilized with Y2 O3 and Lu2 O3 were produced by hot pressing, and the phase structure and room- and high-temperature mechanical properties were assessed. Additional liquid added to the starting composition in the form of 5 wt% rare-earth monosilicate resulted in the formation of elongated microstructures and improvements in room-temperature strength and fracture toughness. The elongated grain growth was promoted by the additional liquid phase, which crystallized to form a secondary grain-boundary phase thought to be J ' (Re4 Si2– x Al x O7+ x N2– x ). For the equiaxed and the elongated samples, those sintered with Lu2 O3 showed higher hardness than the comparable Y2 O3 -sintered materials, and, at elevated temperature, the strength retention of the elongated Lu2 O3 SiAlON was much higher than that of the Y2 O3 sample, which was attributed to properties of the residual grain-boundary phase associated with the difference in the cationic radius of the stabilizing cation. 相似文献
14.
The eutectic composition between Y4 Al2 O9 and Y2 O3 was determined using electron probe microanalysis (EPMA) on directionally solidified specimens with hypo- and hypereutectic compositions. The microstructures of the specimens as a function of composition differ considerably with small deviation from the eutectic composition (70.5 mol% Y2 O3 and 29.5 mol% Al2 O3 ). Based on the current results and other published data, the pseudobinary system between Al2 O3 and Y2 O3 is revised. 相似文献
15.
The phase relations for the system y2 o3 –Ta2 o5 in the composition range 50 to 100 mol% Y2 O3 have been studied by solid-state reactions at 1350°, 1500°, or 17000C and by thermal analyses up to the melting temperatures. Weberite-type orthorhombic phases (W2 phase, space group C2221 ), fluorite-type cubic phases (F phase, space group Fm3m )and another orthorhombic phase (O phase, space group Cmmm )are found in the system. The W2 phase forms in 75 mol% Y2 O3 under 17000C and O phase in 70 mol% Y2 O3 up to 1700°C These phases seem to melt incongruently. The F phase forms in about 80 mol% Y2 O3 and melts congruently at 2454° 3°C. Two eutectic points seem to exist at about 2220°C 90 mol% Y2 O3 , and at about 1990°C, 62 mol% Y2 O3 . A Phase diagram including the above three phases were not identified with each other. 相似文献
16.
Liquidus equilibrium relations for the air isobaric section of the system Y2 O3 –Fe2 O3 –FeO–Al2 O3 are presented. A Complete solid-solution series is found between yttrium iron garnet and yttrium aluminum garnet as well as extensive solid solutions in the spinel, hematite, orthoferrite, and corundum phases. Minimum melting temperatures are raised progressively with the addition of alumina from 1469°C in the system Y–Fe–O to a quaternary isobaric peritectic at 1547°C and composition Y 0.22 Fe 1.08 Al 0.70 O 2.83 * Liquidus temperatures increase rapidly with alumina substitutions beyond this point. The thermal stability of the garnet phase is increased with alumina substitution to the extent that above composition Y 0.75 Fe 0.65 Al 0.60 O 3 garnet melts directly to oxide liquid without the intrusion of the orthoferrite phase. Garnet solid solutions between Y 0.75 Fe 1.25 O 3 and Y 0.75 Fe 0.32- Al 0.93 O 3 can be crystallized from oxide liquids at minimum temperatures ranging from 1469° to 1547°C, respectively. During equilibrium crystallization of the garnet phase, large changes in composition occur through reaction with the liquid. Unless care is taken to minimize temperature fluctuations and unless growth proceeds very slowly, the crystals may show extensive compositional variation from core to exterior. 相似文献
17.
J. LLorca José Y. Pastor Pedro Poza José I. Peña Isabel de Francisco Angel Larrea Victor M. Orera 《Journal of the American Ceramic Society》2004,87(4):633-639
The effect of Y2 O3 content on the flexure strength of melt-grown Al2 O3 –ZrO2 eutectics was studied in a temperature range of 25°–1427°C. The processing conditions were carefully controlled to obtain a constant microstructure independent of Y2 O3 content. The rod microstructure was made up of alternating bands of fine and coarse dispersions of irregular ZrO2 platelets oriented along the growth axis and embedded in the continuous Al2 O3 matrix. The highest flexure strength at ambient temperature was found in the material with 3 mol% Y2 O3 in relation to ZrO2 (Y2 O3 ). Higher Y2 O3 content did not substantially modify the mechanical response; however, materials with 0.5 mol% presented a significant degradation in the flexure strength because of the presence of large defects. They were nucleated at the Al2 O3 –ZrO2 interface during the martensitic transformation of ZrO2 on cooling and propagated into the Al2 O3 matrix driven by the tensile residual stresses generated by the transformation. The material with 3 mol% Y2 O3 retained 80% of the flexure strength at 1427°C, whereas the mechanical properties of the eutectic with 0.5 mol% Y2 O3 dropped rapidly with temperature as a result of extensive microcracking. 相似文献
18.
The mechanism of parahydrogen conversion was studied on Gd2 O3 and Y2 O3 powders and on Gd and Y evaporated metal films at low and high temperatures (77° to 90°K and 298° to 418°K). Absolute rates of conversion are compared to theoretical values for 3 possible reaction mechanisms, and it is concluded that a paramagnetic vibrational mechanism is operative on Gd2 O3 , Gd, and Y. On Y2 O3 the reaction rate is enhanced by additional surface paramagnetic sites. The portion of the surface which is active is ∼1 for the metals and ∼0.01 for the oxides. 相似文献
19.
JONG-HEE PARK WAYNE E. KING STEVEN J. ROTHMAN 《Journal of the American Ceramic Society》1987,70(12):880-885
The cation diffusivities in the lattice and along dislocations and grain boundaries have been measured on sintered polycrysals of Cr2 O3 ; and Cr2 Cr2 O3 -0.09 wt% Y2 O3 at1100°C and at the pO2 corresponding to that of Cr/Cr2 O3 equilibrium at that temperature. Results for lattice and dislocation diffusivities in pure Cr2 O3 are in good agreement with previous work. The present results indicate that yttrium additions have negligible effect on lattice and dislocation diffusion. However, grain-boundary diffusion in pure Cr2 O3 is significantly slower than grain-boundary diffusion in Cr2 O3 -0.09 wt% Y2 O3 . The results are discussed in terms of their implications for the reactive-element effect in high-temperature oxidation of chromium-containing alloys. 相似文献
20.
Osamu Yokota Masatomo Yashima Naoki Yamamoto Masahiro Yoshimura 《Journal of the American Ceramic Society》1997,80(9):2429-2432
Melts of x mol% Ta2 O5 –Y2 O3 (x = 0–32.5) were rapidly quenched to investigate the formation of metastable fluorite solid solutions. C-type Y2 O3 , fluorite, and fergusonite phases existed in the compositional regions of 0 x 16, 8 x 32.5, and 27.5 x 32.5, respectively. Their lattice parameters were precisely measured through either Rietveld analysis or a least-squares fit of the individual X-ray diffraction peak positions. The lattice parameter of the fluorite phase decreased linearly with increasing Ta2 O5 content, strongly suggesting the formation of compositionally homogeneous metastable solid solutions. Ta2 O5 was almost insoluble into Y2 O3 at 1700°C in the equilibrium state. 相似文献