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1.
An all-alkoxide route to films and nano-phase powders of the La0.5 Sr0.5 CoO3 perovskite is described. To our knowledge, this is the first purely alkoxide-based route to (La1− x Sr x )CoO3 , and it yields phase-pure and elementally homogeneous perovskite at 700°C by heating at 2°C/min. At 700°C, a cubic unit cell was obtained with a c =3.853Å, and after further heating to 1000°C, a rhombohedral cell could be indexed: a r =5.417 Å, αr =59.94°. Ninety to 130 nm thick films of La0.5 Sr0.5 CoO3 were obtained by spin coating. The gel-to-oxide conversion was studied in some detail, using thermo-gravimetric analysis, differential scanning calorimetry, powder X-ray diffraction, IR spectroscopy, and transmission electron microscope equipped with an energy-dispersive X-ray spectrometer. 相似文献
2.
Toshio Suzuki Piotr Jasinski Vladimir Petrovsky Harlan U. Anderson 《Journal of the American Ceramic Society》2005,88(5):1186-1189
The effects of microstructure on the optical properties of La0.4 Sr0.6 TiO3 thin films were investigated. Dense films with the thickness of ∼200 nm and grain size 14–30 nm were produced on monocrystalline sapphire substrates by using a polymeric precursor spin coating technique at annealing temperatures under 800°C. X-ray data showed the formation of a single-phase cubic perovskite-type structure similar to undoped SrTiO3 for annealing temperatures >500°C. The results of optical measurements showed that the optical spectra varied with the change of the grain size. From these data, the absorption coefficients were calculated and the band gap energy determined. In agreement with the quantum confinement model, it was shown that the band gap energy increased as the grain size decreased. 相似文献
3.
Jian-Gong Cheng Jun Tang Xiang-Jian Meng Shao-Ling Guo Jun-Hao Chu Min Wang Hong Wang Zhuo Wang 《Journal of the American Ceramic Society》2001,84(7):1421-1424
A sol-gel process was used to prepare pyroelectric Ba0.8 Sr0.2 TiO3 thin films with large columnar grains (100–200 nm in diameter) on Pt/Ti/SiO2 /Si substrates, via using a 0.05 M solution precursor. The relationship between dielectric constant and temperature (ɛr - T ) showed two distinctive phase transitions in the Ba0.8 Sr0.2 TiO3 thin films. Both the remnant polarization and the coercive field decreased as the temperature increased from −73°C to 40°C. Its low dissipation factor (tan δ= 2.6%) and high pyroelectric coefficient ( p = 4.6 × 10−4 C·(m2 ·K)−1 at 33°C), together with its good insulating properties, made the prepared Ba0.8 Sr0.2 TiO3 thin films promising for use in uncooled infrared detectors and thermal imaging applications. 相似文献
4.
Michael Rozumek Peter Majewski Heike Schluckwerder Fritz Aldinger Klaus Künstler Gerhard Tomandl 《Journal of the American Ceramic Society》2004,87(9):1795-1798
Ceramics of the melilite-type compound La1+ x Sr1− x Ga3 O7−δ were prepared by conventional ceramic processing. Samples prepared represented the entire homogeneity region of the phase (i.e., x =−0.15 to 0.60). Electrochemical characterization under variable temperature and atmospheric conditions in the vicinity of air entailed four-point direct-current conductivity measurements and electromotive force measurements. La1+ x Sr1− x Ga3 O7−δ samples exhibited a p -type behavior with generally increased conductivity with increased substitution of lanthanum for strontium, which reached a saturation value of ∼10−1 S·cm−1 at 950°C. 相似文献
5.
Hilde Lea Lein Kjell Wiik Mari-ann Einarsrud Tor Grande Edgar Lara-curzio 《Journal of the American Ceramic Society》2006,89(9):2895-2898
Steady-state compressive creep rate of La0.5 Sr0.5 Fe0.5 Co0.5 O3−δ (LSFC) and La0.5 Sr0.5 CoO3−δ (LSC) is reported in the temperature region 900°–1050°C and stress range 5–28 MPa. The stress exponents for the two materials were 1.71±0.18 and 1.24±0.15, respectively. The activation energy for creep was considerably higher for LSC (619±56 kJ/mol) than for LSFC (392±28 kJ/mol). The grain size exponent for LSC was 1.28±0.14. Considerably higher creep rates were observed for both materials in N2 compared with air. Relaxation by creep of chemical-induced stresses in oxygen-permeable membranes is addressed, especially at low partial pressure of oxygen. 相似文献
6.
Sung Min Rhim Heungjin Bak Seokmin Hong Ok Kyung Kim 《Journal of the American Ceramic Society》2000,83(12):3009-3013
The effects of heating rate on the sintering behavior and the dielectric properties of Ba0.7 Sr0.3 TiO3 ceramics prepared by boron-containing liquid-phase sintering were investigated. When 0.5 wt% B2 O3 was added to Ba0.7 Sr0.3 TiO3 , sintering was achieved at ∼1150°C, and the overdoped B2 O3 did not form an adequate amount of liquid phase or volatilize; it remained in the samples and formed a secondary phase. A transition broadening was observed as the heating rate increased. As the heating rate increased, the Curie temperature increased and the maximum dielectric constant ( k max ) at the Curie temperature decreased. This result is attributable to a decrease in the diffuseness parameter (δ) and the tetragonality ( c / a ). 相似文献
7.
The crystallization behavior of chemical-solution-deposited and amorphous Ba0.7 Sr0.3 TiO3 (BST) thin films was analyzed with respect to the evolution of the structural and dielectric properties of the films as a function of the annealing temperature. The amorphous films were produced by oxygen ion implantation into crystalline BST thin films. In the amorphous thin films, the crystallization to the perovskite phase occurred at T = 550°C, whereas the as-deposited CSD films showed the first crystalline XRD-reflex only after annealing at T = 650°C. Here a carbon-rich intermediate phase delayed the crystallization process to higher temperatures. 相似文献
8.
Yuanhua Lin Ce-Wen Nan Jianfei Wang Gang Liu Junbo Wu Ning Cai 《Journal of the American Ceramic Society》2004,87(4):742-745
The dielectric properties of Na0.5 Bi0.5 TiO3 (NBT) -based composites incorporating silver particles prepared by sintering at a low temperature of ∼900°C are reported. The dielectric constant increases with the amount of metal silver particles in the measured frequency range (150 Hz to 1 MHz), and could be enhanced up to ∼20 times higher than that of pure NBT ceramics, which was ascribed to the effective electric fields developed between the dispersed particles in the matrix and the percolation effect. Further investigation revealed that the dielectric constant of the composites has weak frequency and temperature dependence (−50°C to +50°C). 相似文献
9.
Phase equilibria of the La2 O3 –SrO–CuO system have been determined at 950°C at 30 kbar (3 GPa). Stable phases at the apexes of the ternary phase diagram are CuO, La2 O3 , and SrO. Stable intermediate phases are La2 , CuO4 and La2 Cu2 O5 in the LaO1.5 –CuO binary and Sr2 CuO3 , SrCuO2 , and Sr14 Cu24 O41 in the CuO–SrO binary. The La2– x Sr x -CuO4–δ solid solution is stable for 0.00 is ≤ x ≤ 1.29, the La2– x Sr1+ x Cu2 O6+δ solid solution is stable for 0.03 ≤ x ≤0.20, the La2– x Sr x Cu2 O5–δ solid solution is stable for 0.00 ≤ x ≤1.08, and the La x Sr14– x Cu24 O41 solid solution is stable for 0.00 ≤ x ≤ 6.15. The 30 kbar phase diagram differs from the 1 atm (0.1 MPa) and 10 kbar (1 GPa) results principally in the absence of La1– x Sr2+ x Cu2 O5.5+δ as a stable phase and the extended range of the La2– x Sr x Cu2 O5–δ solid solution at 30 kbar. 相似文献
10.
Phase equilibria of the La2 O3 -SrO-CuO system have been determined at 950°C and 10 kbar (1 GPa). Stable phases at the apices of the ternary phase diagram are CuO, La2 O3 , and SrO. Stable intermediate phases are La2 CuO4 in the LaO1.5 -CuO binary and Sr2 CuO3 , SrCuO2 , and Sr14 Cu24 O41 in the CuO-SrO binary. The La2-x Sr x CuO4-δ solid solution is stable where 0.0 ≤ x ≤ 1.3, the La2-x Sr1+x Cu2 O6+δ solid solution is stable where 0.0 ≤ x ≤ 0.2, the La8-x Sr x Cu8 O20-δ solid solution is stable where 1.3 ≤ x ≤ 2.7, the La x Sr14-x -Cu24 O41 solid solution is stable where 0 ≤ x ≤ 6, and the La1+x Sr2-x Cu2 O5.5+δ phase is stable where 0.04 ≤ x ≤ 0.16. The La2 O3 -SrO-CuO phase diagram at 950°C and 10 kbar is almost identical to that determined by other authors at 950°C and 1 atm, in terms of phase stability and solid-solution ranges. 相似文献
11.
Yoshiho Ito Shiro Shimada Michio Inagaki 《Journal of the American Ceramic Society》1995,78(10):2695-2699
Ba1– x Pb x TiO3 powder with a fixed composition was prepared by the reaction of BaTiO3 powders with molten PbCl2 at various PbCl2 /BaTiO3 molar ratios at 600° and 800°C in a nitrogen atmosphere. When 0.1 μm powder was used, the reaction was finished when x = 0.9. Two phases of BaTiO3 and a solid solution of Ba1– x Pb x TiO3 coexisted, but the final phase gave a solid solution of Ba1– x Pb x TiO3 at 800°C. When 0.5 μm powder was used, the two phases coexisted in the products at 600°C at PbCl2 /BaTiO3 = 1.0. A sintered compact of Ba1– x Pb x TiO3 powders solid solution was prepared by hot isostatic pressing, and its dielectric constant was measured in the temperature range 20°–550°C. 相似文献
12.
Qun Zeng Wei Li Jian-lin Shi Xian-lin Dong Jing-kun Guo 《Journal of the American Ceramic Society》2008,91(2):644-647
A group of new y M-phase/(1− y ) Li2+ x Ti1−4 x Nb3 x O3 composite ceramics with adjustable permittivities for low-temperature co-fired ceramic applications was initially investigated in the study. The 0.5 M-phase/0.5 Li2+ x Ti1−4 x Nb3 x O3 ( x =0.01, 0.02, 0.04, 0.06, 0.081) composite ceramics were first investigated to find the appropriate "Li2 TiO3 ss" composition ( x value). The best dielectric properties of ɛr =40.1, Q × f values up to 9318 GHz, τf =25 ppm/°C, were obtained for the ceramics composites at x =0.02. Based on the good dielectric properties, the suitable "Li2 TiO3 ss" composition with x =0.02 was mixed with the Li1.0 Nb0.6 Ti0.5 O3 powder as the ratio of y "M-phase"/(1− y ) "Li2 TiO3 ss" ( y =0.2, 0.4, 0.5, 0.6, 0.8). By adjusting the y values, the group of composite ceramics could exhibit largely are adjustable permittivities varying from ∼20 to ∼60, while Q × f and τf values relatively good. Nevertheless, in this study, because there are interactions between the M-phase and Li2 TiO3 ss during sintering process, their microwave dielectric properties could not be predicted precisely by the empirical model. 相似文献
13.
The ternary phase diagram of Al2 O3 -La2 O3 -TiO2 at 1400°C was determined with 12 compatibility triangles. Al2 O3 stabilizes the A-site-deficient La2/3 TiO3 perovskite structure. According to XRD and microstructural investigations, the solid solution extends along the La2/3 TiO3 -LaAlO3 tie line from at least 4 mol% LaAlO3 to pure LaAlO3 . With increasing LaAlO3 content, the stabilized La2/3 TiO3 structure changes from orthorombic via tetragonal to cubic. 相似文献
14.
Santanu Basu Amitava Chakraborty Parukuttyamma Sujatha Devi Himadri Sekhar Maiti 《Journal of the American Ceramic Society》2005,88(8):2110-2113
Nanocrystalline La0.9 Sr0.1 Al0.85 Co0.05 Mg0.1 O3 oxide powder was synthesized by a citrate–nitrate auto-ignition process and characterized by thermal analysis, X-ray diffraction, and impedance spectroscopy measurements. Nanocrystalline (50–100 nm) powder with perovskite structure could be produced at 900°C by this process. The powder could be sintered to a density more than 96% of the theoretical density at 1550°C. Impedance measurements on the sintered samples unequivocally established the potential of this process in developing nanostructured lanthanum aluminate-based oxides. The sintered La0.9 Sr0.1 Al0.85 Co0.05 Mg0.1 O3 sample exhibited a conductivity of 2.40 × 10−2 S/cm in air at 1000°C compared with 4.9 × 10−3 S/cm exhibited by La0.9 Sr0.1 Al0.85 Mg0.15 O3 . 相似文献
15.
Ulrich Hasenkox Carsten Mitze Rainer Waser 《Journal of the American Ceramic Society》1997,80(10):2709-2713
A flexible chemical solution deposition (CSD) method for the preparation of magnetoresistive La1−x (Ca,Sr)x MnO3 thin films based completely on metal propionates is pre-sented.A number of polycrystalline thin films with varying stoichiometries were deposited on different substrate ma-terials at temperatures between 550° and 850°C. The crys-tallization behavior on selected substrates was found to de-pend on the thin film stoichiometry. Magnetoresistivity and magnetization were measured as a function of temperature. For the selected samples, a magnetic Curie temperature TC, a metal–semiconductor transition, and magnetoresistive behavior were observed. These measurements demon-strated that La1−x (Ca,Sr)x MnO3 thin films with properties well known from films deposited by PLD or sputtering can be prepared by a simple, propionate-based CSD method. 相似文献
16.
Chun-Hsu Shen Cheng-Liang Huang Chuan-Feng Shih Chih-Ming Huang 《International Journal of Applied Ceramic Technology》2009,6(5):562-570
The microstructure and microwave dielectric properties of a (1− x )(Mg0.95 Ni0.05 )TiO3 − x Ca0.6 La0.8/3 TiO3 ceramics system have been investigated. The system was prepared using a conventional solid-state ceramic route. In order to produce a temperature-stable material, Ca0.6 La0.8/3 TiO3 was added for a near-zero temperature coefficient (τf ). With partial replacement of Mg2+ by Ni2+ , the dielectric properties of the (1− x )(Mg0.95 Ni0.05 )TiO3 − x Ca0.6 La0.8/3 TiO3 ceramics can be promoted. The microwave dielectric properties are strongly correlated with the sintering temperature and the composition. An excellent Q × f value of 118,000 GHz can be obtained for the system with x =0.9 at 1325°C. For practical application, a dielectric constant (ɛr ) of 24.61, a Q × f value of 102,000 GHz, and a temperature coefficient of resonant frequency (τf ) of −3.6 ppm/°C for 0.85(Mg0.95 Ni0.05 )TiO3 −0.15Ca0.6 La0.8/3 TiO3 at 1325°C are proposed. A parallel-coupled line band-pass filter is designed and simulated using the proposed dielectric to study its performance. 相似文献
17.
Kampurath P. Jayadevan Chi-Yi Liu Tseung-Yuen Tseng 《Journal of the American Ceramic Society》2005,88(9):2456-2460
Nanocrystalline x Ag–(1− x )Ba0.5 Sr0.5 TiO3 (Ag–BST, 0≤ x ≤0.1, where x is the mole fraction of Ag) thin films have been deposited on Pt/Ti/SiO2 /Si substrates by a sol–gel method. The films have been characterized by X-ray diffraction (XRD), scanning electron microscopy, and X-ray photoelectron spectroscopy (XPS). The core-level XPS of oxygen (O1 s ) of the Ag–BST films indicate that an optimum amount of Ag ( x =0.02 or 2 mol%) enhances the binding energy of oxygen, possibly through a mechanism in which the electrophilic oxygen dissociates from the Ag surface and fills the oxygen vacancies. Similarly, the binding energy of Ag (Ag3 d ) shows a shift toward a higher value with increasing Ag up to 4 mol%, probably because of the chemical shift of Ag in BST along the surface layers, surface relaxation, or changes in the Fermi level of small Ag particles in the solid solution range of Ag in BST films ( x ≤0.04). The leakage current density of 2 mol% Ag-added BST (∼10−6 A/cm2 ) is less by about an order of magnitude than pure BST at an electric field of 200 kV/cm. A defect model is proposed to explain the observed leakage current density of Ag–BST films satisfactorily. 相似文献
18.
Felipe Gutierrez-Mora Jules L. Routbort 《Journal of the American Ceramic Society》2002,85(9):2370-2372
Pieces of saw-cut La0.85 Sr0.15 MnO3 were joined at 1150° and 1250°C under a compressive stress. The strains to form the joints were ∼0.1. Joints formed by plastic deformation were examined using scanning electron microscopy, and they were indistinguishable from the bulk. The room-temperature direct-current resistivity of the joined pieces was identical to that measured in the bulk material. This indicated that a sound, electrically conducting joint could be formed using plastic deformation (grain-boundary sliding) with little surface preparation. 相似文献
19.
An addition of just 0.4 wt% Li2 O to (Ba0.6 Sr0.4 )TiO3 powder was able to reduce the sintering temperature to ≤900°C and produce ceramics with a relative density of 97%. Small amounts of two secondary phases were formed during this process: Li2 TiO3 and Ba2 TiO4 . The addition of Li2 O depresses the ferroelectric character of the (Ba0.6 Sr0.4 )TiO3 and, as a result, reduces the permittivity, improves the temperature coefficient of permittivity, and reduces the dielectric losses. The tunability shows no significant variation with Li2 O concentration and remains between 16.5% and 13.5%. A low-temperature sintering mechanism was proposed. The mechanism involves the intermediate formation of BaCO3 , its melting and the incorporation of Li+ into the BST. The sintering mechanism can be characterized as reactive liquid-phase sintering. 相似文献
20.
The phase diagram for the CuO-rich part of the La2 O3 ─CuO join was redetermined. La2 Cu2 O5 was found to have a lower limit of stability at 1002°± 5°C and an incongruent melting temperature of ∼1035°C. LagCu7 O19 had both a lower (1012°± 5°C) and an upper (1027°± 5°C) limit of stability. Subsolidus phase relations were studied in the La2 O3 ─CuO─CaO system at 1000°, 1020°, and 1050°C in air. Two ternary phases, La1.9 Ca1.1 Cu2 O5.9 and LaCa2 Cu3 O8.6 , were stable at these temperatures, with three binary phases, Ca2 CuO3 , CaCu2 O3 , and La2 CuO4 . La2 Cu2 O5 and La8 Cu7 O19 were stable only at 1020°C, and did not support solid-solution formation. 相似文献