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1.
Setsuhisa Tanabe Naohiro Saga Kazuyuki Hirao Teiichi Hanada† 《Journal of the American Ceramic Society》1990,73(6):1733-1736
SiO2 –Al2 O3–Eu2 O3 glasses were prepared for the composition 50siO2 ·(50 – x )Al2 O3·x Eu2 O3 , and their density, sound velocity, and elastic modulus were measured. The chemical shift of the AIK a band emission spectra and the isomer shift of 151 Eu by Mössbauer effect were obtained to determine the coordination states of Al3+ and Eu3+ ions in these glasses. It was found that the coordination number of Eu3+ ions was 12 and that the average coordination number of A13+ ions was almost 5 in these glasses. By introducing Eu2 O3 , the packing of constituent ions was strongly enhanced and the elastic modulus increased in this system. The compositional dependence of the molar volume and elastic modulus were explained by these states of high coordination number for Eu3+ and low coordination number for Al3+ ions compared with those in the corresponding M2 O3 crystals. 相似文献
2.
Takahiro Murata Masanori Torisaka Hiromichi Takebe Kenji Morinaga 《Journal of the American Ceramic Society》1998,81(8):2135-2139
Point defects were found in as-quenched GeO2 , 65CaO35Al2 O3 , and 65SrO35Ga2 O3 glasses on the basis of electron paramagnetic resonance (EPR) measurements. These defects were identified as Ge É centers in GeO2 glass and O- 2 , O- 3 , and M-OHC (oxygen hole center) (where M = Al, Ga) in 65CaO35Al2 O3 and 65SrO35Ga2 O3 glasses. The formation of Ge É centers in as-quenched GeO2 glass was due to the thermodynamic stability of GeO at the melting temperature. The latter oxygen-excess defects are supposed to be formed by excess oxygen ions derived from the modifiers in the aluminate and gallate glasses during the formation of these glasses. To investigate some of the properties of the oxygen-excess defects in the calcium aluminate and strontium gallate glasses, chromium ions were doped in these glasses as a probe and the relationship between the valency state of the chromium ion and the defects was determined. We conclude that the peroxy bonding (-O-O-) oxidizes the Cr3+ species to Cr4+ . Similar defects have been identified in host compounds that are used for Cr4+ tunable lasers. These results reveal that the point defects are necessary to stabilize the Cr4+ ions in glasses and crystals. 相似文献
3.
Emission properties and energy transfer of PbO–Bi2 O3 –Ga2 O3 –GeO2 glasses codoped with Tm3+ and Tb3+ ions were investigated. The 1.48-μm emission due to the Tm3+ :3 H4 →3 F4 transition can be used to amplify the S-band (1460–1530-nm) signal light. With Tb3+ addition, the lifetime and emission intensity of the Tm3+ :3 F4 level decreased sharply via the Tm3+ :3 F4 →Tb3+ :7 F0,1,2 energy transfer. Population densities of the 3 F4 and 3 H4 levels in Tm3+ calculated from rate equations clearly verified that population inversion in Tm3+ ions became possible with as little as 0.1 mol% of Tb3+ addition. 相似文献
4.
Tooru Katsumata Kazuhito Sasajima Takehiko Nabae Shuji Komuro Takitaro Morikawa 《Journal of the American Ceramic Society》1998,81(2):413-416
Sr3 Al2 O6 , SrAl2 O4 , SrAl4 O7 , and SrAl12 O19 that have been doped with Eu2+ and Dy3+ ions have been grown by a floating-zone technique for application as long-duration phosphors. Long-duration phosphorescence with a variety of colors has been observed in SrAl2 O4 , SrAl4 O7 , and SrAl12 O19 crystals that have been doped with Eu2+ and Dy3+ ions. The peak wavelength of the phosphorescence is 520 nm for SrAl2 O4 , 480 nm for SrAl4 O7 , and 400 nm for SrAl12 O19 . The phosphorescence is characterized by decay times that have been analyzed by a curve-fitting technique. 相似文献
5.
Ming-Yih Su Christine E. Elsbernd Thomas O. Mason 《Journal of the American Ceramic Society》1990,73(2):415-419
Data for the normal state of the superconducting oxide systems YBa2 Cu3 O6+y , and the nonsuperconducting system La3 Ba3 Cu6 O12.5+y , when plotted as thermoelectric coefficient versus logarithm of conductivity, exhibit Jonker "pear" behavior, confirming the semiconducting character of these materials. The symmetry of the plots indicates similar conduction parameters (density-of-states (DOS), transport constants, and mobilities) for p - and n -type mechanisms. Band gaps on the order of 0.5 eV are obtained. DOS—mobility products for the above-mentioned systems and La2-x Bax CuO4 and Bi2 Sr2 CaCu2 O8 scale roughly according to the density of copper ions in these materials and fall in the range 1020 to 1021 (cm·V·s)−1 . Assuming DOS equal to copper content results in mobilities on the order of 0.15 cm2 ·V−1 · s−1 . These results are discussed in terms of possible semiconduction mechanisms. 相似文献
6.
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
7.
Katsuhisa Tanaka Takash Mukai Tsuguo Ishihara Kazuyuki Hirao Naohiro Soga Seiji Sogo Masaaki Ashida Riso Kato 《Journal of the American Ceramic Society》1993,76(11):2839-2845
Transparent glass-ceramics containing ZnAl2 O4 :Co2+ and LiGa5 O8 :Co2+ crystallites have been prepared by heat treatment of glasses in the zinc aluminosilicate and lithium gallate silicate systems, respectively. Crystalline LiGa5 O8 was already precipitated in an as-prepared specimen, while ZnAl2 O4 :Co2+ precipitated from the glass upon heat treatment. The crystallite size varies from about 5 to 20 nm with increasing heat treatment temperature for both systems, and glass-ceramics containing crystallites of less than about 10 nm are transparent. The low-temperature optical absorption and emission spectra are compared with those of single crystals, indicating that almost all of the Co2+ ions replace Zn2+ ions in the ZnAl2 O4 system, while some of the Co2+ ions are incorporated into the LiGa3 O8 system, although the amount of Co2+ which remains in the glass matrix is rather large in the latter system. 相似文献
8.
On heat treatment in air the solubility of MgO or TiO2 , in Al2 3 is too small to detect by lattice parameter shifts. The solubility of MgTiO3 in Al2 O3 in air increased to the measured values, expressed as atomic fractions Mg:A1or Ti:A1of0.82 × lo-2 , 1.43 × 10-2 , and 1.75 × 10-2 at 1250°, 1650°, and 1850°C, respectively. In 1 atm hydrogen the TiO2 solubility expressed as the atomic fraction Ti:A1 is 0.55 × lo-2 , 0.75 × 10W2 , 1.15 × 10-2 , and 1.50 × 10p2 at 1400°, 1500°, 1600°, and 1700°C, respectively. The increased solubility in H2 was attributed to reduction of the titanium ion. The solubility of MgO in A12 O3 in vacuum (0.3μ) expressed as the atomic fraction Mg:A1 was measured as 1.10 × loW4 , 3.00 × 10"4 , 6.80 × 10–4 , and 1.40 × 10-3 at 1530°, 1630°, 1730°, and 183O°C, respectively. These contents did not cause an observable change in lattice parameter, but a slight change was observed when MgO was dissolved in A12 O3 in a hydrogen atmosphere. 相似文献
9.
C. GRESKOVICH 《Journal of the American Ceramic Society》1970,53(9):498-502
The reaction kinetics for NiCr2 O4 formation and the diffusion of Cr3+ ions into single-crystal NiO were studied between 1300° and 1600°C in air. The experimental activation energy for NiCr2 O4 formation was about 83 kcal/mol. After incubation, NiCr2 O4 formed by a diffusion-controlled process. The origin of pores at the NiO/NiCr2 O4 interface is discussed. The concentration profiles of Cr3+ in NiO were linear because the interdiffusion coefficient was directly proportional to the mol fraction Cr3+ . Theoretical considerations indicate that the interdiffusion coefficient equals 3/2 the self-diffusion coefficient of Cr3+ , which is rate-determining. The interdiffusion coefficient at 1 mol% Cr2 O3 can be expressed as =4×10−3 exp (−55,000/RT) cm2 s−1 . 相似文献
10.
Ehrenfried Zschech Paris N. Kountouros Günter Petzow Peter Behrens Alex Lessmann Ronald Frahm 《Journal of the American Ceramic Society》1993,76(1):197-201
Valence state and site symmetry of Ti ions in TiO2 –Y2 O3 –ZrO2 powders with 2 mol% Y2 O3 and 5, 10, 15, and 20 mol% TiO2 , respectively, are studied by X-ray absorption near-edge spectroscopy (XANES). Tetravalent Zr4+ ions are replaced predominantly by Ti4+ ions. Within the solubility region of Ti ions, a subsequent displacement of Ti ions from the center of symmetry is observed with increasing TiO2 content in TiO2 –Y2 O3 -stabilized tetragonal ZrO2 polycrystals (Ti-Y-TZP) under investigation. This behavior cannot be interpreted with a random substitution of Ti4+ ions on Zr4+ lattice sites. On the contrary, this correlation between the TiO2 content in Ti-Y-TZP and the shift of Ti ions indicates an increasing interaction between the Ti ions with growing TiO2 content, caused by a subsequent clustering of Ti ions. 相似文献
11.
Darko Makovec Irena Priboic Zoran Samardija Miha Drofenik 《Journal of the American Ceramic Society》2001,84(11):2702-2704
The solid solubility of the aliovalent dopants Fe3+ and Nb5+ in the BaBi4 Ti4 O15 compound, a member of the family of Aurivillius bismuth-based layer-structure perovskites, has been studied using quantitative wavelength-dispersive spectroscopic microanalysis (SEM/EPMA) in combination with X-ray powder diffractometry (XRPD). The samples with nominal (starting) compositions corresponding to the chemical formulas BaBi4 Ti4–4 X Fe4 X O15 and BaBi4 Ti4–4 X Nb4 X O15 were prepared by hot forging a mixture of BaTiO3 and Bi4 Ti3 O12 with additions of Fe2 O3 or Nb2 O5 followed by a long annealing at 1100°C. The study showed that an excess charge introduced into the structure by the substitution of Ti4+ ions with aliovalent dopants was preferentially compensated by a change in the ratio of Ba2+ to Bi3+ ions in the host structure according to the general formulas of the solid solutions Ba1–4 X Bi4+4 X Ti4–4 X Fe' 4 X O15 and Ba1+4 X Bi4–4 X Ti4–4 X Nb· 4 X O15 . 相似文献
12.
Yuan-Hua Lin Ming Li Ce-Wen Nan Zhongtai Zhang 《Journal of the American Ceramic Society》2007,90(9):2992-2994
CaAl2 O4 -based phosphors with Eu2+ and La3+ codoped have been prepared by the traditional solid-sintering method, and the photoluminescence intensity can be efficiently enhanced by codoped La3+ ions. Positron annihilation spectroscopy proves that a large amount of vacancies exist in the CaAl2 O4 host and the complex defects form on increasing the concentration of doped La3+ ions. The thermoluminescence spectra demonstrate that some new trap levels with various trap depths are produced on increasing the concentration of the doped La3+ ions, which are correlated to the La3+ -associated complex defects in the CaAl2 O4 -based phosphor. 相似文献
13.
Low-Temperature Fabrication of Cordierite Ceramics from Kaolinite and Magnesium Hydroxide Mixtures with Boron Oxide Additions 总被引:3,自引:0,他引:3
Katsuhiro Sumi Yuichi Kobayashi Etsuro Kato 《Journal of the American Ceramic Society》1999,82(3):783-785
Thermal reactions of mixtures of ultrafine particles of magnesium hydroxide (Mg(OH)2 ) and kaolinite in a composition of MgO:Al2 O3 :2SiO2 were investigated to obtain dense cordierite ceramics at temperatures <1000°C. While heating the mixture of kaolinite and Mg(OH)2 with the equivalent of 2 mass% of boron oxide (B2 O3 ) (in the form of magnesium borate, 2MgOB2 O3 ), an amorphous phase formed at a temperature of ∼850°C after thermal decomposition. Firing the mixture at a temperature of 900°C yielded dense ceramics with an apparent porosity of almost zero. The addition of B2 O3 promoted the densification at 850°-900°C and accelerated the crystallization of alpha-cordierite. The specimen with 3 mass% of B2 O3 that was fired at a temperature of 950°C showed a linear thermal expansion coefficient of ∼3 × 10−6 K−1 , a bending strength of >200 MPa, and a relative dielectric constant of 5.5 at 1 MHz. These cordierite ceramics may be used as substrate materials for semiconductor interconnection applications. 相似文献
14.
Jie Fu 《Journal of the American Ceramic Society》1997,80(7):1901-1903
Fast lithium ion conducting glass-ceramics have been successfully prepared from the pseudobinary system 2[Li1+ x Ti2 Si x P3− x O12 ]-AlPO4 . The major phase present in the glass-ceramics was LiTi2 P3 O12 in which Ti4+ ions and P5+ ions were partially replaced by Al3+ ions and Si4+ ions, respectively. Increasing x resulted in a considerable enhancement in conductivity, and in a wide composition range extremely high conductivity over 10−3 S/cm was obtained at room temperature. 相似文献
15.
Daniel Caurant Odile Majérus Edward Fadel Marion Lenoir Christel Gervais Olivier Pinet 《Journal of the American Ceramic Society》2007,90(3):774-783
Crystallization of the poorly durable Na2 MoO4 phase able to incorporate radioactive cesium must be avoided in SiO2 –Al2 O3 –B2 O3 –Na2 O–CaO glasses developed for the immobilization of Mo-rich nuclear wastes. Increasing amounts of B2 O3 and MoO3 were added to a SiO2 –Na2 O–CaO glass, and crystallization tendency was studied. Na2 MoO4 crystallization tendency decreased with the increase of B2 O3 concentration whereas the tendency of CaMoO4 to crystallize increased due to preferential charge compensation of BO4 − entities by Na+ ions. 29 Si MAS NMR showed that molybdenum acts as a reticulating agent in glass structure. Trivalent actinides surrogate (Nd3+ ) were shown to enter into CaMoO4 crystals formed in glasses. 相似文献
16.
Alumina powders with varying iron oxide contents were prepared by coprecipitation. The powders were spheroidized by passing them through an oxygen-acetylene flame. The spheres were sized, annealed, and sintered in air and in N2 with 132 ppm O2 . Isothermal studies were combined with constant-rate-of-heating studies to identify the mechanism of sintering and to calculate the diffusion coefficients. The contribution of surface diffusion during initial-stage sintering of Fe-doped Al2 O3 was estimated by combining shrinkage and neck-growth data. The effect of Ti on the sintering rate of Fe-doped Al2 O3 was also studied. Both Fe2+ and Ti4+ ions enhanced the sintering rate of Al2 O3 . A defect model for corundum is proposed to explain the sintering data for transition-metal-ion-doped Al2 O3 . 相似文献
17.
Transparent Cr4+-Doped YAG Ceramics for Tunable Lasers 总被引:1,自引:0,他引:1
Akio Ikesue Kunio Yoshida Kiichiro Kamata 《Journal of the American Ceramic Society》1996,79(2):507-509
Transparent Cr4+ :YAG (Y3 AlS O12 ) ceramics doped with Ca and Mg as counterions and SiO2 as a sintering aid were fabricated by a solid-state reaction method using high-purity powders of Al2 O3 , Y2 O3 , and Cr2 O3 . The mixed powder compacts were sintered at 1750°C for 10 h in oxygen, or 1750°C for 10 h under vacuum, and then annealed at 1400°C for 10 h in oxygen. Cr-doped YAG ceramics sintered in oxygen had a brown color and characteristic absorption by Cr4+ ions, whereas these YAG ceramics sintered under different conditions (vacuum + oxygen) had a green color and absorption at ∼590 and 430 nm by Cr3+ ions. The absorption behavior of YAG ceramics sintered in oxygen was almost equivalent to that of Cr4+ :YAG single crystals fabricated by the Czochralski method. 相似文献
18.
The effect of Cr and Fe in solid solution in γ-Al2 O3 on its rate of conversion to α-Al2 O3 at 1100°C was studied by X-ray diffraction. The δ form of Al2 O3 was the principal intermediate phase produced from both pure γ-Al2 O3 and that containing Fe3+ in solid solution, although addition of Fe greatly reduced crystallinity. Reflectance spectra and magnetic susceptibilities showed that Cr exists as Cr6+ in γ-Al2 O3 and as Cr3+ in α-Al2 O3 , with θ-Al2 O3 as the intermediate phase. The intermediates formed rapidly, and the rates of their conversion to α-Al2 O3 were increased by 2 and 5 wt% additions of Fe and decreased by 2 and 4 wt% additions of Cr. An approximately linear relation observed between α-Al2 O3 formation and decrease in specific surface area was only slightly affected by the added ions. This relation can be explained by a mechanism in which the sintering of δ- or θ-Al2 O3 , within the aggregates of their crystallites, is closely coupled with conversion of cubic to hexagonal close packing of O2- ions by synchro-shear. 相似文献
19.
Zhen-Yan Deng Fang-Fang Xu Jihong She Yoshihisa Tanaka Yoshio Bando 《Journal of the American Ceramic Society》2004,87(3):493-495
In this work, 800 ppm of Zr4+ dopants were added to Al2 O3 -5 vol% SiC particle composite. Zr4+ doping led to a weak Al2 O3 grain-boundary bonding so that the fracture mode changed from transgranular in undoped composite to intergranular in Zr4+ -doped composite. The fracture mode change increased the fracture toughness of the composite. Transmission electron microscopy and energy-dispersive spectroscopy examinations revealed that the weak grain-boundary bonding in the doped composite was caused by the segregation of Zr4+ and Si4+ ions at the Al2 O3 grain boundary. 相似文献
20.
Diffusion of Iron and Nickel in Magnesium Oxide Single Crystals 总被引:1,自引:0,他引:1
Diffusion kinetics and mechanisms were studied in the Fex O-MgO (vacuum), NiO-MgO (vacuum and air), and Fe2 03 -MgO (air) systems. In the Fex O-MgO system, Fe entered MgO by a redox reaction; the diffusivity and activation energy depended on concentration. In the NiO-MgO system in air the diffusivity depended on concentration and the activation energy did not; in vacuum both the diffusivity and activation energy were concentration-independent. In the Fe2 O3 -MgO system in the MgO phase the activation energy and diffusivity did not depend on concentration. Because of impurities, the diffusion results were for the extrinsic region. Formation of trivalent ions and consequent chemically created vacancies in the Fex O-MgO and NiO-MgO (air) systems resulted in the concentration dependence of diffusivity. Concentration dependence of activation energy in the Fex O-MgO system is associated with structural changes due to a change with concentration of the Fe3+ octahedraI/Fe3+ tetrahedral ratio. In the Fe2 O3 -MgO system structural changes do not occur during diffusion because this ratio remains constant. 相似文献