共查询到20条相似文献,搜索用时 31 毫秒
1.
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
2.
Sea-Fue Wang K. Koteswara Rao Yuh-Ruey Wang Yung-Fu Hsu Shih-Hsin Chen Yi-Ching Lu 《Journal of the American Ceramic Society》2009,92(8):1732-1738
A series of rare earth molybdates, Y2− x Eu x (MoO4 )3 for x =0.4, 0.8, 1.2, 1.6 and 2.0 were prepared by solid-state method and their crystal structures, photo luminescent characteristics were investigated. The powders are mainly studied for their red light emission efficiency under near UV excitation. The crystal structures of the powders were found to depend on annealing temperature and the yttrium concentration. Mixtures of monoclinic ( C 2 /c ) and orthorhombic ( Pba 2, Pbna ) structures were formed in varying proportions depending on the value of x and annealing temperatures (700°–800°C). The luminescence behavior depended on the resultant composition of the crystal phase and the Eu3+ concentration. The excitation spectra showed the characteristic and broad O→Mo charge transfer (CT) band of the MoO4 tetrahedra and the sharp intra-configurational 4 f –4 f transitions of Eu3+ in the host lattice. The integrated emission ratio (5 D0 →7 F2 /5 D0 →7 F1 ) of Eu3+ depends on the annealing temperature and reveals that the local site symmetry of Eu3+ ions decreases with increasing concentration of Eu3+ . The emission spectra obtained by exciting at 396 nm, gave highest red emission intensity for Y0.4 Eu1.6 (MoO4 )3 annealed at 700°C/6 h among this series of samples. 相似文献
3.
Shinobu Fujihara Shinnosuke Koji Yasuhiro Kadota Toshio Kimura 《Journal of the American Ceramic Society》2004,87(9):1659-1662
Pr3+ -doped YF3 (orthorhombic), YO0.80 F1.40 (orthorhombic), YOF (rhombohedral), and Y2 O3 (cubic) films were synthesized on quartz-glass substrates through pyrolysis of a single-source trifluoroacetate precursor at temperatures between 400° and 900°C in air. Phase-selective deposition was achieved by controlling heating temperature and time. YF3 , which formed first from the precursor, was transformed to YO0.80 F1.40 , YOF, and Y2 O3 . Photoluminescent properties of Pr3+ -doped films were examined using ultraviolet excitation. An intense green photoluminescence was observed in the YOF:Pr3+ film, which was deposited at 700°C, through an efficient charge transfer (O2− –Pr3+ ) excitation. 相似文献
4.
Zhong Zhuang Xian Ping Wang Dan Li Tao Zhang Qian Feng Fang 《Journal of the American Ceramic Society》2009,92(4):839-844
Dense, crack-free, and uniform La2 Mo2− x W x O9 ( x =0, 0.1, and 0.2) nanocrystalline films were successfully synthesized on poly-alumina substrates via a modified sol–gel method, with inorganic salt of La(NO3 )3 ·6H2 O, (NH4 )6 Mo7 O24 ·4H2 O, and (NH4 )6 H2 W12 O24 as precursors. Pure La2 Mo2 O9 phase was confirmed by X-ray diffractometer when the annealing temperature was >500°C. The average grain size of the La2 Mo2− x W x O9 films is in the range of 90–400 nm, depending upon the conditions of thermal treatment, and the thickness of films can reach 1 μm by repetitive spin-coating. The electrical conductivity increases with decreasing grain size and reaches 0.074 S/cm at 600°C in the film with a grain size of 90 nm, which is one order of magnitude higher than that in the corresponding bulk materials. W-doping can suppress the phase transition that occurs at 580°C in pure La2 Mo2 O9 and enhance the low-temperature ionic conductivity. Furthermore, the activation energy of conductivity in the nanocrystalline La2 Mo2 O9 films decreases to about 0.6 eV in comparison with 1.0 eV in the bulk ones, which implies that the grain resistance prevails in the total resistance, when grain size reduces to nanometer domain. 相似文献
5.
Yun Chan Kang Hyun Sook Roh Seung Bin Park 《Journal of the American Ceramic Society》2001,84(2):447-49
Na2 CO3 flux was introduced in the preparation of phosphor particles by spray pyrolysis to improve the photoluminescence (PL) characteristics of (Y0.5 Gd0.5 )2 O3 :Eu phosphor particles. The phosphor particles directly prepared by spray pyrolysis at 1300°C from solutions with 20 wt% Na2 CO3 flux had the highest PL intensity, which corresponded to 130% of that of particles prepared from solution without flux. On the other hand, the maximum PL intensity of the annealed particles, which were as-prepared at 900°C and posttreated at 1200°C for 3 h, was obtained from a solution with 5 wt% Na2 CO3 flux. The maximum PL intensity of particles directly prepared by spray pyrolysis without posttreatment was 86% of that of posttreated phosphor particles. Na2 CO3 flux was also important in control of morphology of (Y0.5 Gd0.5 )2 O3 :Eu phosphor particles. 相似文献
6.
Li+ ions have been successfully doped into the La sites of (La0.95 Eu0.05 )2 Ti2 O7 nanocrystals through a facile citric acid sol–gel method. The doping concentration of Li+ ions can be as high as 15 mol%. Photoluminescence (PL) performances of the obtained samples have been investigated. The results showed that a doping with small number of Li+ ions improves the PL intensity of the synthesized La2 Ti2 O7 :Eu3+ nanophosphors. The highest emission intensity was observed using the formula of (La0.92 Eu0.05 Li0.03 )2 Ti2 O7 , whose brightness was increased by almost 20% in comparison with that of (La0.95 Eu0.05 )2 Ti2 O7 . 相似文献
7.
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
8.
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
9.
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
10.
Hisanori Yamane Kazuhiro Ogawara Mamoru Omori Toshio Hirai 《Journal of the American Ceramic Society》1995,78(9):2385-2390
Lattice parameters of RE4 Al2 O9 (RE = Y, Sin, Eu, Gd, Tb, Dy, Ho, Er, Tm, and Yb) prepared at 1600–1800°C and those of RE4 Ga2 O9 (RE = La, Pr, Nd, Sm, Eu, and Gd) prepared at 1400–1600°C were refined by Rietveld analysis for the X-ray powder diffraction patterns. The parameters increased linearly with the ionic radius of the trivalent rare-earth elements ( r RE ). High-temperature differential calorimetry and dilatometry revealed that both RE4 Al2 O, and RE4 Ga2 O, have reversible phase transitions with volume shrinkages of 0.5–0.7% on heating and thermal hystereses. The transition temperatures (7tr ) decreased from 1300°C (Yb) to 1044°C (Sm) for RE4 A12 O9 , except for Y4 Al2 O9 ( Ttr = 1377°C), and from 1417°C (Gd) to 1271°C (La) for RE4 Ga2 O, with increasing ionic radius of the rare-earth elements. These transition temperatures were plotted on a curve against the ionic radius ratio of Al3+ or Gd3+ and RE3+ ( r A1 Ga /rRE ) except for Y4 Al2 O9 . 相似文献
11.
Subsolidus phase relations were established in the system Si3 N4 -SiO2 -Y2 O3 . Four ternary compounds were confirmed, with compositions of Y4 Si2 O7 N2 , Y2 Si3 O3 N4 , YSiO2 N, and Y10 (SiO4 )6 N2 . The eutectic in the triangle Si3 N4 -Y2 Si2 O7 -Y10 (SiO4 )6 N2 melts at 1500°C and that in the triangle Si2 N2 O-SiO2 -Y2 Si2 O7 at 1550°C. The eutectic temperature of the Si3 N4 -Y2 Si2 O7 join was ∼ 1520°C. 相似文献
12.
Yoshihito Mizoguchi Masahiro Kagawa Yasuhiko Syono Toshio Hirai 《Journal of the American Ceramic Society》2001,84(3):651-653
Thin films of yttrium aluminum garnet (YAG, Y3 Al5 O12 ) and yttrium iron garnet (YIG, Y3 Fe5 O12 ) were synthesized on single-crystal Al2 O3 substrates by a modification of spray pyrolysis using a high-temperature inductively coupled plasma at atmospheric pressure (spray–ICP technique). Using this technique, films could be grown at faster rates (0.12 μm/min for YAG and 0.10 μm/min for YIG) than using chemical vapor deposition (0.005–0.008 μm/min for YAG) or sputtering (0.003–0.005 μm/min for YIG). The films were dense and revealed a preferred orientation of (211). The growth of YIG was accompanied by coprecipitation of α-Fe2 O3 . The coprecipitation, however, could be largely suppressed by preliminary formation of a Y2 O3 layer on the substrate. 相似文献
13.
Pb(Mg1/3 Ta2/3 )0.7 Ti0.3 O3 thin films of single perovskite phase were successfully synthesized by using the RF sputtering deposition technique, followed by post-thermal annealing. While the perovskite structure of Pb(Mg1/3 Ta2/3 )0.7 Ti0.3 O3 is rather unstable, phase evolution in the thin films was manipulated by controlling both working pressure during the sputtering process and post-thermal annealing temperature. The desirable perovskite phase was promoted by increasing the working pressure in the range of 10–25 mTorr, followed by thermal annealing at 600°C. The ferroelectric, dielectric, and polarization behaviors of Pb(Mg1/3 Ta2/3 )0.7 Ti0.3 O3 films were characterized over a wide range of frequencies. They are strongly affected by the film thickness, where the relative permittivity and remanent polarization increase, while the coercive field decreases with increasing film thickness in the range of 115–360 nm. 相似文献
14.
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
15.
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
16.
Single-phase garnet solid solutions can be synthesized between the composition limits of x =4.18 and x =4.22 in Y2.66 Gd0.34 Fe x Al0.677 Mn0.09 O12 at temperatures between 1340° and 1500°C in O2 . Solid solutions occur only on the Y2 O3 -excess side of the stoichiometric garnet composition. Electromagnetic properties and microstructural features of sintered garnets depend critically on small changes in Fe content in the vicinity of the garnet solid-solution region. An intergranular spinel-type second phase exists for compositions when x >4.22 and has a deleterious effect on remanent induction and magnetic loss at 3 GHz. The relative density of powder compacts sintered for 16 h at 1500°C in O2 increases with increasing Fe content (i.e. as x increases) in the garnet solid solution. 相似文献
17.
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
18.
Microstructure and Properties of Co2+ : ZnAl2 O4 /SiO2 Nanocomposite Glasses Prepared by Sol–Gel Method
Xiu-Lan Duan Duo-Rong Yuan Xiu-Feng Cheng Hai-Qing Sun Zhi-Hong Sun Xin-Qiang Wang Zeng-Mei Wang Dong Xu Meng-Kai Lv 《Journal of the American Ceramic Society》2005,88(2):399-403
Transparent bulk Co2+ : ZnAl2 O4 /SiO2 nanocomposites containing nanocrystalline Co2+ : ZnAl2 O4 dispersed in silica glass matrix were obtained by the sol–gel method. The gels of composition 89SiO2 –6Al2 O3 –5ZnO− x CoO ( x =0.2, 0.4, 0.6, 0.8, 1.0) (mol%) were prepared at room temperature by using two different aluminum salts, aluminum nitrate and aluminum alkoxide (aluminum-iso-propoxide, Al(OPri )3 ), as starting materials. The transparent gels were converted to the crystalline phase of gahnite by heating above 900°C. The microstructural evolution of gels was characterized. The effect of Co2+ concentration on spectroscopic properties was also discussed. Co2+ : ZnAl2 O4 nanocrystals dispersed in the SiO2 -based glass are formed at lower heat-treatment temperature and shorter heating time by using Al(OPri )3 as raw material. 相似文献
19.
Several unusual microstructural features, i.e., 90° tetragonal ZrO2 twins containing antiphase domain boundaries, tetragonal ZrO2 precipitates in a colony morphology, and precipitate-free zones at the perimeter of cubic ZrO2 grains containing fine tetragonal ZrO2 precipitates, were observed in a single ZrO2 -12 wt% Y2 O2 ceramic annealed at 1550°, 1400°, and 1250°C, respectively. The type of phase transformation responsible for each microstructural feature is described. 相似文献
20.
The effects of substituting Nb5+ with Ta5+ on the microwave dielectric properties of the ZnNb2 O6 ceramics were investigated in this study. The forming of Zn(Nb1− x Ta x )2 O6 ( x =0–0.09) solid solution was confirmed by the measured lattice parameters and the EDX analysis. By increasing x , not only could the Q × f of the Zn(Nb1− x Ta x )2 O6 ( x =0–0.09) solid solution be tremendously boosted from 83 600 GHz at x =0 to a maximum 152 000 GHz at x =0.05, the highest ɛr ∼24.6 could also be achieved simultaneously. It was mainly due to the uniform grain morphology and the highest relative density of the specimen. A fine combination of microwave dielectric properties (ɛr ∼24.6, Q × f ∼152 000 GHz at 8.83 GHz, τf ∼–71.1 ppm/°C) was achieved for Zn(Nb0.95 Ta0.05 )2 O6 solid solution sintered at 1175°C for 2 h. 相似文献