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1.
Yoshio Sakka Yasumichi Oishi Ken Ando Shoji Morita 《Journal of the American Ceramic Society》1991,74(10):2610-2614
Zr–Hf interdiffusions were carried out at 1350° to 1520°C for polycrystalline tetragonal solid solutions of 14CeO2 ·86(Zr1- x Hf x )O2 with X = 0.02 and 0.10. Lattice and grain-boundary interdiffusion parameters were calculated from the concentration distributions by using Oishi and Ichimura's equation. Lattice interdiffusion coefficients were described by D = 3.0 × 103 exp[-623 (kJ/mol)/ RT ] cm2 /s and grain-boundary interdiffusion parameters by δ D ' = 0.29 exp[-506 (kJ/mol)/ RT ] cm3 /s. The cation diffusivity was lower than the anion diffusivity. The results were compared with diffusivities in the fluorite-cubic solid solution. The critical grain radii for stabilization of the tetragonal phase in CeO2 -doped ZrO2 were 11 and 6 μm for the solutions with 2 and 10 mol% HfO2 substitution, respectively, both of which are much greater than in the Y2 O3 -doped ZrO2 solid solution. 相似文献
2.
Interdiffusion coefficients were determined in single-crystal (Ca,Sr)F2 solid solutions in the temperature range 1100° to 1320°C. The composition dependence of the coefficients passes through a maximum that shifts toward higher CaF2 concentrations at higher temperatures. Extrapolation of the interdiffusion coefficient to extremes of composition provides impurity diffusion coefficients that agree well with tracer results. The changes in activation energy with composition can be explained readily on the basis of cationic radii and lattice parameters. 相似文献
3.
Yoshio Sakka Yasumichi Oishi Ken Ando Yoji Ikeda 《Journal of the American Ceramic Society》1993,76(5):1381-1383
Zr–Hf interdiffusion was studied in the temperature range of 1650° to 1850°C in air for polycrystalline fluorite-cubic systems of 90CeO2 ·10(Zr1- x Hf x )O2 and 60CeO2 ·40(Zr1- x Hf x )O2 . Lattice and grain-boundary diffusion parameters were calculated from the Zr–Hf concentration distributions by using the grain-boundary diffusion equation of Oishi and Ichimura. The cation iattice diffusivity was close to that in the fluorite-cubic Y2 O2 -ZrO2 solid solution. 相似文献
4.
A microprobe study of interdiffusion between 1033° and 1238°C in the system SrF2 -BaF2 was conducted using single crystals. The interdiffusion coefficient, D , generally decreased with increasing SrF2 concentration, but the composition dependence of D decreased with decreasing temperature. Extrapolation of D values to infinite dilution allowed the impurity cation self- diffusion coefficients:
The values for DSr in BaF2 are in excellent agreement with tracer results. An analysis of the activation energies for cations diffusing in alkaline-earth fluorides shows a direct correlation between constriction ratio and migration energy for a single ion diffusing in different fluorides. An apparent anomaly arises when attempting to correlate migration energy with structural information for different cations diffusing in the same fluoride. 相似文献
The values for D
5.
Pavel Diko Paul.-H. Duvigneaud Alain Lanckbeen ré Van Moer Georges Naessens Robert Deltour 《Journal of the American Ceramic Society》1993,76(11):2859-2864
Porosity, grain growth, phase composition, and microstructural defects were studied in sintered YBa2 (Cu1−x )3 O7−x ceramics for x values up to 0.3. The porosity of the samples, related to the sintering mechanism, was independent of iron concentration. A linear dependence of the grain size with the inverse of the iron concentration was found, strongly suggesting grain boundary segregation of iron. The solubility limit was estimated to be x = 0.18 at 950°C in O2 . Beyond this limit, a new microstructural component was found consisting of YBa2 (Cu1−x Fex )3 O7−δ , YBaCuFeO5 and Ba(Cu,Fe)O2 . The transition from an orthorhombic twin to an orthorhombic tweed phase and a tetragonal phase was detected by polarized light microscopy. 相似文献
6.
Kazunari Sasaki Petr Bohac Ludwig J. Gauckler 《Journal of the American Ceramic Society》1993,76(3):689-698
Phase equilibria in the system ZrO2 ─InO1.5 have been investigated in the temperature range from 800° to 1700°C Up to 4 mol%, InO1.5 is soluble in t -ZrO2 at 1500°C. The martensitic transformation temperature m → t of ZrO2 containing InO1.5 is compared with that of ZrO2 solid solutions with various other trivalent ions with different ionic radii. The diffusionless c → t ' A phase transformation is discussed. Extended solid solubility from 12.4 ± 0.8 to 56.5 ± 3 mol% InO1.5 is found at 1700°C in the cubic ZrO2 phase. The eutectoid composition and temperature for the decomposition of c -ZrO2 solid solution into t -ZrO2 +InO1.5 solid solutions were determined. A maximum of about 1 mol% ZrO2 is soluble in bcc InO1.5 phase. Metastable supersaturation of ZrO2 in bcc InO 1.5 and conditions for phase separation are discussed. 相似文献
7.
Single-phase, cubic solid solutions of baseline composition 25% Y2 O3 —75% Bi2 O3 with and without aliovalent dopants were fabricated by pressureless sintering of powder compacts. CaO, SrO, ZrO2 , or ThO2 was added as an aliovalent dopant. Sintered samples were annealed between 600° and 650°C for up to 4000 h. Samples doped with ZrO2 or ThO2 remained cubic, depending upon the dopant concentration, even after long-term annealing. By contrast, undoped, CaO-doped, and SrO-doped samples transformed to the low-temperature, rhombohedral phase within ∼ 200 h. Conductivity measurements showed no degradation of conductivity in samples that did not undergo the transformation. In samples that underwent the transformation, a substantial decrease in conductivity occurred. The enhanced stability of the ZrO2 - and ThO2 -doped samples is rationalized on the basis of suppressed interdiffusion on the cation sublattice. 相似文献
8.
Activity-composition relations in Mn-Co orthosilicate and metasilicate solid solutions were determined at 1200° to 1250°C by equilibrating selected phase assemblages with metallic cobalt and a gas phase of known oxygen potentials at a total pressure of 1 atm. The orthosilicate solid solution shows a slight negative departure from ideality, whereas the metasilicate solid solution is ideal. The stability data derived for the Mn2 SiO4 and MnSiO3 end-members are in good agreement with those previously determined from the system MnO-"FeO"-SiO2 . The free-energy change for the reaction 2CoSiO3 = Co2 -SiO4 + SiO2 was determined to be -3.8 kcal at 1250°C. 相似文献
9.
R. G. VISSER† W. F. SCHIAVI‡ M. F. BERARD 《Journal of the American Ceramic Society》1975,58(9-10):438-441
An electron microprobe interdiffusion study was made in single crystals between 1200° and 1331°C over the solid-solution compositional range 0 to 20 mol% YF3 in CaF2 . At constant temperature, the value of δ , the interdiffusion coefficient, increased approximately exponentially with increasing YF3 content. As YF3 content increased, the temperature dependence of δ decreased. Extrapolation of δ to 0% YF3 combined with consideration of the defect formation mechanism at mite dilution allowed estimation of the impurity diffusion coefficient for Y in essentially pure CaF2 . 相似文献
10.
Kuan Zong Fung Anil V. Virkar David L. Drobeck 《Journal of the American Ceramic Society》1994,77(6):1638-1648
Cubic solid solutions in the Y2 O3 -Bi2 O3 system with ∼25% Y2 O3 undergo a transformation to a rhombohedral phase when annealed at temperatures ≤ 700°C. This transformation is composition-invariant and is thermally activated, and the product phase can propagate across matrix grain boundaries, indicating that there is no special crystallo-graphic orientation relationship between the product and the parent phases. Based on these observations, it is proposed that cubic → rhombohedral phase transformation in the Y2 O3 -Bi2 O3 system is a massive transformation. Samples of composition 25% Y2 O3 -75% Bi2 O3 with and without aliovalent dopants were annealed at temperatures ≤ 700°C for up to 10000 h. ZrO2 as a dopant suppressed while CaO and SrO as dopants enhanced the kinetics of phase transformation. The rate of cubic/rhombohedra1 interface migration (growth rate or interface velocity) was also similarly affected by the additions of dopants; ZrO2 suppressed while CaO enhanced the growth rate. Diffusion studies further showed that ZrO2 suppressed while CaO enhanced cation interdiffusion coefficient. These observations are rationalized on the premise that cation interstitials are more mobile compared to cation vacancies in cubic bismuth oxide. The maximum growth rate measured was ∼10−10 m/s, which is orders of magnitude smaller than typical growth rates measured in metallic alloys. This difference is explained in terms of substantially lower diffusion coefficients in these oxide systems compared to metallic alloys. 相似文献
11.
AlN, Al2 OC, and the 2 H form of SiC are isostructural. Both SiC–AlN and AlN–Al2 OC form homogeneous solid solutions above 2000° and 1950°C, respectively. The kinetics of phase separation in the two systems, however, are quite different. Interdiffusion in both SiC–AlN and AlN-Al2 OC systems was examined in the solid-solution regime in an attempt to elucidate differences in the kinetics of phase separation that occur in the two systems when annealed at lower temperatures. Diffusion couples of (SiC)0.3 (AlN)0.7 /(SiC)0.7 (AlN)0.3 and (AlN)0.7 (Al2 OC)0.3 /(AlN)0.3 (Al2 OC)0.7 were fabricated by hot pressing and were annealed at high temperatures by encapsulating them in sealed SiC crucibles to suppress loss due to evaporation. Interdiffusion coefficients in (SiC)0.3 -(AlN)0.7 /(SiC)0.7 (AlN)0.3 diffusion couples were measured at 2373, 2473, and 2573 K, and the corresponding activation energy was determined to be 632 kJ/mol. (AlN)0.7 (Al2 OC)0.3 / (AlN)0.3 (Al2 OC)0.7 samples were annealed at 2273 K. The interdiffusion coefficient measured in the AlN–Al2 OC system was much larger than that in the SiC–AlN system. 相似文献
12.
Takayuki Komatsu Chisai Hirose Tomohiro Ohki Kazumasa Matusita 《Journal of the American Ceramic Society》1990,73(12):3569-3574
Superconducting coupling nature at grain boundaries in Bi2 Sr2 CaCu2 O x glass-ceramics consisting mainly of the low- T c phase was first examined by measuring superconducting properties and temperature or ac field dependence of ac complex susceptibility. It was found from the ac loss peaks that superconducting coupling at grain boundaries was basically characterized by three types of weak links. The weak-link behaviors at grain boundaries depended strongly on cooling conditions after annealing and annealing time and temperature. Particularly, it was found that the weak links at grain boundaries were improved by prolonged annealing at 840°C. The furnace-cooled glass-ceramics obtained by annealing at 820° or 840°C for about 200 h exhibited a critical transport current density (77 K, zero magnetic field) of about 200 A/cm2 . 相似文献
13.
Grain growth in a high-purity ZnO and for the same ZnO with Bi2 O3 additions from 0.5 to 4 wt% was studied for sintering from 900° to 1400°C in air. The results are discussed and compared with previous studies in terms of the phenomenological kinetic grain growth expression: G n — G n 0 = K 0 t exp(— Q/RT ). For the pure ZnO, the grain growth exponent or n value was observed to be 3 while the apparent activation energy was 224 ± 16 kJ/mol. These parameters substantiate the Gupta and Coble conclusion of a Zn2+ lattice diffusion mechanism. Additions of Bi2 O3 to promote liquidphase sintering increased the ZnO grain size and the grain growth exponent to about 5, but reduced the apparent activation energy to about 150 kJ/mol, independent of Bi2 O3 content. The preexponential term K 0 was also independent of Bi2 O3 content. It is concluded that the grain growth of ZnO in liquid-phase-sintered ZnO-Bi2 O3 ceramics is controlled by the phase boundary reaction of the solid ZnO grains and the Bi2 O3 -rich liquid phase. 相似文献
14.
Yoshio Sakka Yasumichi Oishi Ken Ando Masaaki Masuda 《Journal of the American Ceramic Society》1989,72(11):2121-2125
Cation inter diffusion in cubic C-type solid solutions was investigated for the polycrystalline systems Y2 O3 —Zrx Hf1 -x-1 O2 and Y2 O3 –ZrO2 in the small-grain, deep-penetration condition at 1615° to 1822°C. Lattice and grain-boundary diffusion parameters were calculated from cation concentration distributions by using Oishi and Ichimura's grain-boundary diffusion equation. The results indicated that Zr–Y and Zr–Hf interdiffusion coefficients decreased with an increase in Y content. The cation diffusivities were lower than anion diffusivities, and the interdiffusion parameters were lower in the C-type cubic than in fluorite-type cubic solid solutions. The results were compared with diffusivities in other C-type cubic oxides. 相似文献
15.
The influence of Nd2 O3 doping on the reaction process and sintering behavior of BaCeO3 is investigated. Formation of BaCeO3 is initiated at 800°C and completed at 1000°C. When Nd2 O3 is added to the starting materials, the formation of BaCe1–x Ndx O3–δ is delayed and the temperature for complete reaction is increased to 1100°C. Only a BaCe1-x Ndx O3–δ solid solution with an orthorhombic crystal structure is present in the specimens for x ≤ 0.1. A secondary phase rich in Ce and Nd is formed within grains and at grain boundaries, when the Nd2 O3 content is greater than the solubility limit (x ≥ 0.2). Pure BaCeO3 is difficult to sinter, even at 1500°C, and only a porous microstructure could be obtained. However, doping BaCeO3 with Nd2 O3 markedly enhances its sinterability. The enhancement of the sinterability of Nd2 O3 -doped specimens at x ≤ 0.1 is attributed to the increase in the concentration of oxygen ion vacancies, which increases the diffusion rate. At x ≥ 0.2, the grain size is abnormally coarsened, which is caused by the formation of a liquid phase. While this liquid phase accelerates sintering, its beneficial effect on densification is counteracted by the segregation of the secondary grain-boundary phase which inhibits sintering. 相似文献
16.
The Li2 O-TiO2 pseudobinary phase diagram was determined from 50 to 100 mol% TiO2 by DTA, microscopy, and X-ray analysis; Li2 Ti3 O7 effectively melts congruently at 1300° and decomposes eutectoidally at 940°C. A solid solution based on Li2 TlO3 from 50 to ∼65 mol% TiO3 was observed to exist at >930°C. A new metastable phase was discovered with a composition of ∼75 mol% TiO2 and with a hexagonal unit cell (8.78 by 69.86 × 10−1 nm). Discrepancies in the literature regarding some of these phase equilibria are reconciled. 相似文献
17.
Chen Li Yuan Cailei Xue Junmin John Wang 《Journal of the American Ceramic Society》2005,88(11):3279-3282
Phase formation behaviors of double perovskite Sr2 FeMoO6 (SFMO) derived from mechanical activation were investigated. Polycrystalline double perovskite SFMO of grain sizes in nanometer range were synthesized by heat treatment of the precursors derived from mechanical activation of SrO, Fe2 O3 , and MoO3 at temperatures in the range of 600°–900°C in flowing atmosphere of H2 /Ar. Mechanical activation at room temperature led to formation of SFMO at 700°C, which is about 200°C lower than what is required in the conventional solid state reaction. The magnetization of thus-derived SFMO increases with increasing heat-treatment temperature in the range of 700°–900°C. Similarly, its magnetoresistance ratio also increases with increasing heat-treatment temperature, which is accounted for by the elimination of insulating SrMoO4 impurity phase and enhancement in crystallinity of the double perovskite SFMO phase. 相似文献
18.
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
19.
Hwi-Yeol Park Cheol-Woo Ahn Kyung-Hoon Cho Sahn Nahm Hyeung-Gyu Lee Hyung-Won Kang Duk-Hee Kim Kyeong-Soon Park 《Journal of the American Ceramic Society》2007,90(12):4066-4069
The sintering temperature of 0.95(Na0.5 K0.5 )NbO3 –0.05BaTiO3 (NKN–BT) ceramics needs to be decreased below 1000°C to prevent Na2 O evaporation, which can cause difficulties in poling and may eventually degrade their piezoelectric properties. NKN–BT ceramics containing CuO were well sintered at 950°C with grain growth. Poling was easy for all specimens. Densification and grain growth were explained by the formation of a liquid phase. The addition of CuO improved the piezoelectric properties by increasing the grain size and density. High piezoelectric properties of d 33 =230 pC/N, k p =37%, and ɛ3 T /ɛ0 =1150 were obtained from the specimen containing 1.0 mol% of CuO synthesized by the conventional solid-state method. 相似文献
20.
KUNIHITO KOUMOTO HIROAKI YANAGIDA SUSUMU MIZUTA 《Journal of the American Ceramic Society》1980,63(1-2):17-20
The mechanism for the evaporation of ZnO from powders of (Zn02 Co0.8 )O·Al2 O3 (ZCA) and (Zn0.2 Ni0.8 )O·Al2 O3 (ZNA) spinels was studied at 1335° to 1500°C in vacuum of 3×10−5 to 10−4 torr. The evaporation of ZnO occurred in two stages: at a constant rate in the first and a decreasing rate in the second. The rate-determining process was analyzed as a decomposition reaction at the first stage and as the conjugated process of decomposition reaction and diffusion in the solid at the second. The evaporation rate constant and surface emissivity showed a similar dependence on temperature. The ratio of the concentration of ZnO at the surface to the initial concentration was =0.7 when the first stage of evaporation changed to the second. 相似文献