共查询到20条相似文献,搜索用时 15 毫秒
1.
Basak Yazgan Kokuoz Karn Serivalsatit Baris Kokuoz Olt Geiculescu Exley McCormick John Ballato 《Journal of the American Ceramic Society》2009,92(10):2247-2253
Nanoparticles of erbium-doped yttria (Er:Y2 O3 ) are important precursors to transparent ceramics for high-power solid-state lasers systems. As structure influences properties and, subsequently, performance the purpose of this work is to compare the morphological and chemical nature of the nanoparticles synthesized using two common methods: solution precipitation and combustion synthesis. A thorough characterization of as-prepared and calcined powders was performed using Fourier transform infrared spectroscopy, X-ray diffraction, conventional and high-resolution transmission electron microscopy, and Brunauer–Emmet–Teller methods. Solution precipitation was found to lead to two different precursor compositions (yttrium carbonate or yttrium hydroxide) depending on the precipitating reagent whereas combustion synthesis yielded only phase-pure, cubic Er:Y2 O3 . The hydroxide precipitation and combustion synthesis methods exhibited agglomerated particles with low surface area after calcining the precursors at 900°C. The addition of a small amount of ammonium sulfate during combustion synthesis was found to reduce the level of agglomeration, resultant particle size, and degree of crystallinity of the calcined Er:Y2 O3 nanoparticles. The amount of carbon dioxide (CO2 ) and water (H2 O) on the surface of the Er:Y2 O3 powders is dependent on the powder surface area, however, increasing levels of gas absorption on the particle surfaces do not have a detrimental effect on the sinterability. The sintered density increases with increasing surface area and decreasing agglomeration. 相似文献
2.
F. G. BUTTLER L. S. DENT GLASSER H. F. W. TAYLOR 《Journal of the American Ceramic Society》1959,42(3):121-126
Single-crystal X-ray and electron-diffraction studies show the existence in one polymorph of 4CaO.Al2 O3 . 13H2 O of a hexagonal structural element with α= 5.74 a.u., c = 7.92 a. u. and atomic contents Ca2 (OH)7 - 3H2 O. These structural elements are stacked in a complex way and there are probably two or more poly-types as in SiC or ZnS. Hydrocalumite is closely related to 4CaO.A12 O3 .13H2 O, from which it is derived by substitution of CO3 2- for 20H- + 3H2 O once in every eight structural elements; similar substitutions explain the existence of compounds of the types 3CaO Al2 O3 .Ca Y 2 - xH2 O and 3CaO Al2 O3 Ca Y xH2 O. On dehydration, 4CaO.Al2 O3 .13H2 O first loses molecular water and undergoes stacking changes and shrinkage along c. At 150° to 250°C., Ca(OH)2 and 4CaO.3Al2 O3 .3H2 O are formed and, by 1000°C., CaO and 12CaO.7Al2 O8 . The dehydration of hydrocalumite follows a similar course, but no 4CaO.3Al2 O3 .3H2 O is formed. 相似文献
3.
Ji-Guang Li Takayasu Ikegami Toshiyuki Mori Yoshiyuki Yajima 《Journal of the American Ceramic Society》2004,87(6):1008-1013
Hydroxyl-type Sc2 O3 precursors have been synthesized via precipitation at 80°C with hexamethylenetetramine as the precipitant. The effects of starting salts (scandium nitrate and sulfate) on powder properties are investigated. Characterizations of the powders are achieved by elemental analysis, X-ray diffractometry (XRD), differential thermal analysis/thermogravimetry (DTA/TG), high-resolution scanning electron microscopy (HRSEM), and Brunauer-Emmett-Teller (BET) analysis. Hard-aggregated precursors (γ-ScOOH·0.6H2 O) are formed with scandium nitrate, which convert to Sc2 O3 at temperatures ≥400°C, yielding nanocrystalline oxides of low surface area. The use of sulfate leads to a loosely agglomerated basic sulfate powder having an approximate composition of Sc(OH)2.6 (SO4 )0.2 ·H2 O. The powder transforms to Sc2 O3 via dehydroxylization and desulfurization at temperatures up to 1000°C. Well-dispersed Sc2 O3 nanopowders (∼64.3 nm) of high purity have been obtained by calcining the basic sulfate at 1000°C for 4 h. The effects of SO4 2− on powder properties are discussed. 相似文献
4.
Junying Zhang Zhongtai Zhang Zilong Tang Yuanhua Lin 《Journal of the American Ceramic Society》2002,85(4):998-1000
A (Ce0.67 Tb0.33 )Mn x Mg1− x Al11 O19 phosphor powder was synthesized, using a simple sol–gel process, by mixing citric acid with CeO2 , Tb4 O7 , Al(NO3 )3 ·9H2 O, Mg(OH)2 ·4MgCO3 ·6H2 O, and Mn(CH3 COO)2 . The phosphor crystallized completely at 1200°C, and the phosphor particle size was between 1 and 5 μm. The excitation spectrum was characteristic of Ce3+ , while the emission spectrum was composed of lines from Tb3+ and Mn2+ . The Mn2+ gave a green fluorescence band, and concentration quenching occurred when x > 0.10. The luminescent properties of the phosphor were explained by a configurational coordinate model. 相似文献
5.
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
6.
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
7.
Structural evolution in the X-ray amorphous precursors to La2 Sn2 O7 and La2 Ti2 O7 is examined using IR and Raman spectroscopy. These precursors are prepared by rapid coprecipitation from mixed aqueous solutions of the corresponding metal chlorides. Rapid coprecipitation from an SnCl2− 6 and La3+ -containing aqueous solution yields microcrystalline particles of SnO2 · n H2 O and La(OH)3 , which instantaneously interconnect to form an ultimate, complex colloid particle. The Ti(OH)2+ 2 and La3+ in the other solution system coprecipitate into a different, complex colloid (an unidentified phase), which is definitely not a mixed dispersion of single-component colloids. A comparative examination of the vibrational spectra of the coprecipitates heated to various temperatures indicates that the SnO2 and anatase phases develop in the respective precursors before crystallization of the desired double oxides. Crystallization itself can be attributed to a solid-state reaction among the various microcrystallites of each single-metal oxide in a gel particle of the precursor. 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.
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
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.
Jing-Feng Li Ryuzo Watanabe Bo-Ping Zhang Katsuhiko Asami Koji Hashimoto 《Journal of the American Ceramic Society》1996,79(12):3109-3112
2 mol% Y2 O3 -ZrO2 polycrystals were annealed in water and under vacuum to highlight the effect of the presence of H2 O on the low-temperature degradation transformation. The specimen surfaces with monoclinic phases transformed during annealing in the different environments were analyzed by X-ray photoelectron spectroscopy with special interest on the electron binding energy change of the constituent ions of the 2 mol% Y2 O3 -ZrO2 ceramics after the degradation transformation. It was found that no change occurred for the electron-bonding energies of core levels of zirconium ions after the transformation, whereas Y-OH bonds were formed during annealing in water. This result suggested a possibility that the preferred hydration of yttrium took place at the surface of Y2 O3 -partially-stabilized ZrO2 , which is likely to be the reason for the low-temperature degradation accelerated by the presence of H2 O. 相似文献
12.
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
13.
Krzysztof Borowiec Jan Przyluski Krystyna Kolbrecka 《Journal of the American Ceramic Society》1991,74(8):2007-2010
The intrinsic kinetics, unaffected by diffusional and masstransfer effects, of the CO2 degradation of superconducting particles have been determined using a nonisothermal technique. Below 900°C, the carbonization of YBa2 Cu3 O7- x leads to formation of BaCO3 , Y2 Cu2 O5 , CuO, and Cu2 O. A further increase in temperature results in formation of BaCuO2 from BaCO3 and CuO. The carbonization rate shows the 1.5th-order dependence on the amount of unreacted YBa2 Cu3 O7- x for the temperature range of 550° to 815°C. The activation energy of carbonization was determined to be 95.1 kJ · mol−1 . 相似文献
14.
Debao Zhang Baoyu Chen Zhuping Liu Shunguang Li Lili Hu 《Journal of the American Ceramic Society》2004,87(12):2228-2231
Er3+ -doped sodium lanthanum aluminosilicate glasses with compositions of (90− x )(0.7SiO2 ·0.3Al2 O3 )· x Na2 O·8.2La2 O3 · 0.6Er2 O3 ·0.2Yb2 O3 ·1Sb2 O3 (in mol%) ( x = 12, 20, 24, 40, 60 mol%) were prepared and their spectroscopic properties were investigated. Judd–Ofelt analysis was used to calculate spectroscopic properties of all glasses. The Judd–Ofelt intensity parameter Ω t ( t = 2, 4, 6) decreases with increasing Na2 O. Ω2 decreases rapidly with increasing Na2 O while Ω4 and Ω6 decrease slowly. Both the fluorescent lifetime and the radiative transition rate increase with increasing Na2 O. Fluorescence spectra of the 4 I 13/2 to 4 I 15/2 transition have been measured and the change with Na2 O content is discussed. It is found that the full width at half-maximum decreases with increasing Na2 O. 相似文献
15.
Ho-Yong Lee Chan-Joong Kim Gye-Won Hong 《Journal of the American Ceramic Society》1996,79(11):2912-2916
The formation of spherical pores and regions free of Y2 BaCuO5 (2-1-1) has been studied by melt processing Y1.6 Ba2.3 Cu3.3 O x: in two different atmospheres (air and oxygen). When the sintered Y1.6 Ba2.3 Cu3.3 O x specimens are melted at 1050°C, many spherical pores form in the melted specimens. During the subsequent cooling, the pores are filled by liquid flow and finally solidified to Y2 BaCuO5 -free regions. Melt processing in an oxygen atmosphere produces more pores and regions free of 2-1-1 than in air. Because peritectic melting of YBa2 Cu3 O7-y in an oxygen atmosphere produces more oxygen gas than that in air, the formation of the pores and Y2 BaCuO5 -free regions is suggested to be attributed to the oxygen evolution during the peritectic melting of YBa2 Cu3 O7−y 相似文献
16.
Adam J. G. Ellison Paul C. Hess Gerald C. Naski 《Journal of the American Ceramic Society》1998,81(12):3215-3220
The saturation surface of cassiterite, SnO2 , was determined for liquids in the system K2 O–Al2 O3 –SiO2 as a function of bulk composition and temperature. At fixed K2 O/Al2 O3 cassiterite solubility varies weakly with SiO2 concentration (76 to 84 mol%), temperature (1350° to 1550°C), and log ( f O 2 ) (−0.7 to −5.3). Cassiterite solubility is also approximately independent of composition in liquids with molar ratios of K2 O/Al2 O3 lessthan equal to 1 (peraluminous liquids). As K2 O/Al2 O3 increases from 1 (peralkaline liquids), however, cassiterite solubility increases steeply and approximately linearly with K2 O in excess of Al2 O3 . It is proposed that potassium in excess of aluminum combines with Sn4+ to form quasi-molecular complexes with an effective stoichiometry of K4 SnO4 . 相似文献
17.
Masayuki Nogami Naoya Hayakawa Naoya Sugioka Yoshihiro Abe 《Journal of the American Ceramic Society》1996,79(5):1257-1261
Samarium ions (Sm2+ ) incorporated into aluminosilicate glasses by a sol-gel process showed persistent spectral hole burning at room temperature. Gels of the system Na2 O-Al2 O3 SiO2 synthesized by the hydrolysis of Si(OC2 H5 )4 , Al(OC4 H9 )3 , CH3 COONa, and SmCl3 ·6H2 O were heated in air at 500°C, then reacted with H2 gas to form Sm2+ ions. Whereas Al3+ ions effectively dispersed the Sm3+ ions in the glass structure, Na+ ions were not effective. The Al2 O3 -SiO2 glasses proved appropriate for reacting the Sm3+ ions with H2 gas and exhibited the intense photoluminescence of Sm2+ ions. The reaction of Sm3+ ions with H2 in the Al2 O2 -SiO2 glasses was determined by first-order kinetics, and the activation energy equaled 95 kJ/mol. At 800°C, the maximum photoluminescence of the Sm2+ ions was achieved within 20 min. 相似文献
18.
The precursor [NH4 ]2 [Ti(catecholate)3 ] · 2H2 O is known to react with Ba(OH)2 · 8H2 O in an acid/base process that generates Ba[Ti(catecholate)3 ] · 3H2 O, a compound which undergoes low-temperatue calcination to produce BaTiO3 powder. Attempts to develop similar routes to PbTiO3 have been frustrated, since lead(II) hydroxide does not exist. The amphoteric yellow PbO and the basic oxide, Pb6 O(OH)6 4+ , are both insufficiently basic to react with [NH4 ]2 [Ti(catecholate)3 ] · 2H2 O. Based on the large sizes of both the [Ti(catecholate)3 ]2- anion and the Pb2+ cation, a precipitation method has been developed in which lead nitrate and [NH4 ]2 [Ti(catecholate)3 ] · 2H2 O are added together in an aqueous medium causing precipitation and leaving only NH4 NO3 in solution. The lead-titanium-catecholate complex that forms in this manner undergoes low-temperature pyrolysis to produce PbTiO3 . SEM indicates a submicrometer ultimate crystallite size. 相似文献
19.
Zinc oxide (ZnO) nanoparticles coated with 1–5 wt% Bi2 O3 were prepared by precipitating a Bi(NO3 )3 solution onto a ZnO precursor. Transmission electron microscopy showed that a homogeneous Bi2 O3 layer coated the surface of the ZnO nanoparticles and that the ZnO particle size was ∼30–50 nm. Scanning electron microscopy showed that ZnO grains sintered at 1150°C were homogeneous in size and surrounded by a uniform Bi2 O3 layer. When the ZnO grains were surrounded fully by Bi2 O3 liquid phases, further increases in the ZnO grain size were not affected by the Bi2 O3 content. This predesigned ZnO nanoparticle structure was shown to promote homogeneous ZnO grains with perfect crystal growth. 相似文献
20.
Microstructural changes occurring during oxidation of the reduced form of donor-doped BaTiO3 (Ba1− X D X . Ti1− X 4+ Ti X 3+ O3 ) and during reduction of the oxidized form of donor-doped BaTiO3 (Ba1− X D X . Ti1− X /4 4+ ( V Ti ) X /4 O3 ) were studied using TEM. Samples of both types of solid solutions, containing different La concentrations (from 2 to 20 mol% La), were prepared by sintering under reducing conditions and in air, respectively. The reduced form of donor-doped BaTiO3 was oxidized by annealing at high temperatures (1150° and 1350°C) in air, while the oxidized form was reduced by annealing under reducing conditions. Because of oxidation of the reduced phase of donor-doped BaTiO3 , the Ti-rich phases Ba6 Ti17 O40 and BaLa2 Ti4 O12 were precipitated. Reduction of the oxidized form caused precipitation of the Ba-rich phase Ba2 TiO4 preferentially inside the matrix grains. All precipitates had well-defined orientational relationships with the perovskite matrix. 相似文献