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1.
Xuebin Zhu Shoubao Zhang Hechang Lei Xiangde Zhu Gang Li Bosen Wang Wenhai Song Zhaorong Yang Jianming Dai Yuping Sun Dongqi Shi Shixue Dou 《Journal of the American Ceramic Society》2009,92(4):800-804
Metallic and transparent La0.5 Sr0.5 TiO3+ x /2 films were prepared by the chemical solution deposition (CSD) method using topotactic reduction processing. The use of Si powder as the reducing agent was facile and allowed easy manipulation. It was observed that metallic (resistivity at 300 K ∼2.43 mΩ cm) and transparent (∼80% transmittance at visible light) La0.5 Sr0.5 TiO3+ x /2 films could be obtained with an annealing temperature of 900°C, which was significantly lower than the hydrogen reduction temperature (∼1400°C). The successful preparation of metallic and transparent La0.5 Sr0.5 TiO3+ x /2 films using CSD has provided a feasible route for depositing other perovskite-structured functional layers on La0.5 Sr0.5 TiO3+ x /2 films using this low-cost all CSD method. 相似文献
2.
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
3.
La0.8 Sr0.2 Cr0.9 Ti0.1 O3 perovskite has been designed as an interconnect material in high-temperature solid oxide fuel cells (SOFCs) because of its thermal expansion compatibility in both oxidizing and reducing atmospheres. La0.8 Sr0.2 Cr0.9 Ti0.1 O3 shows a single phase with a hexagonal unit cell of a = 5.459(1) Å, c = 13.507(2) Å, Z = 6 and a space group of R -3 C . Average linear thermal expansion coefficients of this material in the temperature range from 50° to 1000°C were 10.4 × 10−6 /°C in air, 10.5 × 10−6 /°C under a He–H2 atmosphere (oxygen partial pressure of 4 × 10−15 atm at 1000°C), and 10.9 × 10−6 /°C in a H2 atmosphere (oxygen partial pressure of 4 × 10−19 atm at 1000°C). La0.8 Sr0.2 Cr0.9 Ti0.1 O3 perovskite with a linear thermal expansion in both oxidizing and reducing environments is a promising candidate material for an SOFC interconnect. However, there still remains an air-sintering problem to be solved in using this material as an SOFC interconnect. 相似文献
4.
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
5.
Liang Fang Heping Su Qian Yu Hui Zhang Bolin Wu 《Journal of the American Ceramic Society》2008,91(8):2769-2771
A high dielectric constant and low-loss ceramic with composition Sr4 LaTiNb3 O15 has been prepared by the conventional solid-state ceramic route. This compound adopts an A5 B4 O15 cation-deficient hexagonal perovskite structure and crystallizes in the trigonal system with unit cell parameters a =5.6307(2), c =11.3692(3) Å, V =312.16(2) Å3 , and Z =1. The dielectric properties of dense ceramics sintered in air at 1460°C have been characterized at microwave frequencies. The results show that the material affords a relatively high dielectric constant ɛr ∼43, a high quality factor Q × f ∼44 718 GHz, and a low temperature coefficient of resonant frequency TCf ∼13 ppm/°C. 相似文献
6.
Rejini Rajamma Mailadil Thomas Sebastian 《Journal of the American Ceramic Society》2007,90(8):2472-2475
The microwave dielectric properties of two A-site-deficient perovskite-type ceramics in the La6 Mg4 A2 W2 O24 [A=Ta and Nb] system were investigated. The compounds were synthesized by the solid-state ceramic route. The structure and microstructure were analyzed using X-ray diffraction and scanning electron microscopy techniques. The dielectric properties were measured in the microwave frequency range [4–6 GHz] by the resonance method. La6 Mg4 Ta2 W2 O24 had Q u × f =13 600 GHz, ɛr =25.2, and τf =−45 ppm/°C and La6 Mg4 Nb2 W2 O24 had Q u × f =16 400 GHz, ɛr =25.8, and τf =−56 ppm/°C. 相似文献
7.
Hyun-Jai Kim Sergey Kucheiko Seok-Jin Yoon Hyung-Jin Jung 《Journal of the American Ceramic Society》1997,80(5):1316-1318
Dielectric properties of the system (1 − x)(La1/2 Na1/2 )TiO3 – x Ca(Fe1/2 Nb1/2 )O3 , where 0.4 # x # 0.6, have been investigated at microwave frequencies. The temperature coefficient of resonant frequency (τf ), nearly 0 ppm/°C, was realized at x = 0.58. These ceramics had perovskite structure and showed relatively low dielectric losses. A new dielectric material applicable to microwave devices having Q · f of 12000–14000 GHz and a dielectric constant (εr ) of 59–60 has been obtained at 1300–1350°C for 5–15 h sintering. 相似文献
8.
Guttamindapalli A. Ravi Feridoon Azough Robert Freer Robert J. Cernik Anthony M. T. Bell 《Journal of the American Ceramic Society》2007,90(12):3947-3952
Mixed-oxide prepared Ca0.7 Ti0.7 La0.3 Al0.3 O3 (CTLA) ceramics (≈96% dense), grain size 6–7 μm, with dielectric properties (at 4 GHz) of ɛr ≈46, Q × f ≈38 000 GHz, and τf +13 ppm/°C, were studied at 25°–1300°C using synchrotron X-ray powder diffraction. At room temperature, CTLA exhibits a distorted orthorhombic structure, with two tilt systems: a =5.40383 (4) Å, b =5.41106 (6) Å, and c =7.64114 (7) Å with space group Pbnm . At 1050°±25°C, there is a transition from orthorhombic ( Pbnm ) to tetragonal ( I 4/ mcm ), with a simpler tilt arrangement. The lattice parameters at 1100°C were: a =5.44285 (4) Å and c =7.68913 (8) Å. 相似文献
9.
Cone-shaped Sm-doped CeO2 (Ce0.8 Sm0.2 O1.9 , SDC) electrolyte cylinders have been fabricated using the slip-casting technique. A single solid oxide fuel cell has been prepared by applying a Sm0.5 Sr0.5 CoO3 cathode on the outside of the cylinders and a NiO–SDC (7:3 wt%) anode on the inside. The open circuit voltage of the cell was 0.93 V at 400°C, and a maximum power density of about 300 mW/cm2 at 700°C was obtained with humidified hydrogen (3% H2 O) as the fuel and ambient air as the oxidant. Impedance results showed that the performance of the cell was mainly influenced by the ohmic resistance of the electrolyte. 相似文献
10.
Pure and 5 wt% of Ag-doped (La1− x Y x )2 Ba2 CaCu5 Oz superconducting compounds for x =0–0.5 have been prepared. Analysis of X-ray diffraction patterns shows that the samples are essentially in the single-phase form and they could be refined using the P 4 /mmm space group in a tetragonal cell. The typical lattice parameters are found to be a = b =3.879 Å, c =11.646 Å for x =0 and a = b =3.856 Å, c =11.576 Å for x =0.5 samples. The detailed crystal structure parameters are presented. The average grain size values from scanning electron microscope images are found to be in the order of 1–3 μm. Temperature variations of ac susceptibility and electrical resistivity have been measured. Superconducting transitions with diamagnetic T c ranging from 60 to 75 K have been observed, with the maximum T c for the x =0.25 sample. Ag-doped samples exhibit improved inter-granular coupling and homogeneous oxygenation. 相似文献
11.
Kjersti Kleveland Nina Orlovskaya Tor Grande Anne Marie Mardal Moe Mari-Ann Einarsrud Kristin Breder George Gogotsi 《Journal of the American Ceramic Society》2001,84(9):2029-2033
LaCoO3 and La0.8 Ca0.2 CoO3 ceramics show a nonelastic stress–strain behavior during four-point bending experiments where hysteresis loops are observed during loading–unloading cycles. Permanent strain is stored in the material after unloading, and a mechanism related to ferroelastic domain switching in the rhombohedral perovskite is proposed. Domain switching in the materials has been confirmed using X-ray diffractometry. Fracture toughnesses of La0.8 Ca0.2 CoO3 measured using single-edge notched beam and single-edge V-notched beam methods coincide and are equal to 2.2 MPa·m1/2 at room temperature and decrease to ∼1 MPa·m1/2 at temperatures >300°C. A decrease in fracture toughness is consistent with ferroelastic behavior, because the rhombohedral distortion decreases with increasing temperature. 相似文献
12.
JOSEPH T. LEWANDOWSKI ROBERT A. BEYERLEIN JOHN M. LONGO RONALD A. McCAULEY 《Journal of the American Ceramic Society》1986,69(9):699-703
The K2 NiF4 -type phase in the La-Co-O system has been studied and vacancy formation on both the lanthanum and oxygen sublattices has been observed. The formula La2 CoO4 has generally been accepted for the K2 NiF4 -type phase in the La-Co-O system. However, a broad range of lattice constants are reported for this material, indicative of variations in composition. More recently, a range of stoichiometries has been suggested in the literature which is represented by the formula La2 CoO4+x . The variations in stoichiometry have previously been explained by the presence of excess oxygen or by inter-growths of Ruddlesden-Popper-type phases, (AO(ABO3 )n ). In this work, X-ray diffraction data confirmed the previous variations in lattice parameters but indicated that the material is lanthanum deficient, not rich in oxygen. Thermogravimetric analysis confirmed the existence of variable oxygen stoichiometry. These data were consistent with a range of compositions described by the general formula La1.83 CoO4-x , where 0 ≤ x ≤ 0.13. These materials contain a maximum of 50% trivalent cobalt when x = 0. In addition, thermo-gravimetric experiments in lower partial pressures of oxygen have enabled us to isolate a new, fully reduced form, La1.83 CoO3.75 , which contains only divalent cobalt. A two- phase region exists between La1.83 CoO3.75 and La1.83 CoO3.87 . 相似文献
13.
Antonio Feteira Lisa J. Gillie Ralf Elsebrock Derek C. Sinclair 《Journal of the American Ceramic Society》2007,90(5):1475-1482
The crystal structure and dielectric properties of LaYbO3 ceramics prepared by the mixed-oxide route have been investigated. Rietveld refinements performed on X-ray and neutron diffraction data show the room-temperature structure to be best described by the orthorhombic Pnma space group [ a =6.02628(9) Å, b =8.39857(11) Å, and c =5.82717(7) Å; Z =4, and theoretical density, D x =8.1 g/cm3 ] in agreement with electron diffraction experiments. LaYbO3 ceramics fired at 1600°C for 4 h attain ∼97% of D x and their microstructures consist of randomly distributed equiaxed grains with an average size of ∼8 μm. Conventional transmission electron microscopy shows densification to occur in the absence of a liquid phase and reveals domain-free grains. The relative permittivity, ɛr , of LaYbO3 ceramics at radio frequencies is ∼26 in the range ∼10–300 K; however, a small dielectric anomaly is detected at ∼15 K. At room temperature and microwave frequencies, LaYbO3 ceramics exhibit ɛr ∼26, Q × f r ∼20 613 GHz (at 7 GHz), and τf ∼−22 ppm/K. Q × f r show complex subambient behavior, decreasing from a plateau value of ∼20 000 GHz between ∼300 and 200 K to a second plateau value of ∼6000 GHz at ∼90 K before decreasing to <1000 GHz at ∼10 K. The large decrease in Q × f r at low temperature may be related to the onset of antiferromagnetism at ∼2.7 K. 1 相似文献
14.
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
15.
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
16.
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
17.
Michael Rozumek Peter Majewski Linda Sauter Fritz Aldinger 《Journal of the American Ceramic Society》2003,86(11):1940-1946
Phase stability studies were performed within the quasi-ternary system LaGaO3 -SrGaO2.5 -"LaMgO2.5 ". Emphasis was cast on the temperature dependence of the homogeneity region of La1− x Sr x Ga1− y Mg y O3−δ perovskite solid solutions. Isothermal sections were determined at 1100°, 1250°, 1400°, and 1500°C in a static air atmosphere. The single-phase homogeneity region was found to considerably diminish with decreasing temperature, indicating a reduction of the solid solubility of Sr and Mg, and below 1100°C the doped perovskite becomes unstable. Consequently, the cubic perovskite phase was found to exist only at elevated temperatures and for high Sr and Mg amounts. Sample preparation was performed by the mixed-oxide process as well as by a modified combustion synthesis. 相似文献
18.
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
19.
Rajamma Rejini Mailadil Thomas Sebastian 《International Journal of Applied Ceramic Technology》2006,3(3):230-235
The La5 CrTi3 O15 and La4 MCrTi3 O15 (M=Pr, Nd, and Sm) microwave dielectric ceramics were prepared by the conventional solid-state ceramic route. The structure and microstructure of the ceramics were studied by X-ray diffraction and scanning electron microscopy methods. The dielectric properties of the ceramics were measured in the microwave frequency region using a network analyzer by the resonance method. The ceramics show a dielectric constant (ɛr ) in the range of 37 to 39.5, a quality factor ( Q u × f o ) 17,300 to 34,000 GHz, and a temperature coefficient of resonant frequency (τf ) in the range from −22 to −38 ppm/°C. 相似文献
20.
Bo Wei Zhe Lü Xiqiang Huang Zhiguo Liu Jipeng Miao Na Li Wenhui Su 《Journal of the American Ceramic Society》2007,90(10):3364-3366
A cobalt-free perovskite oxide, Ba0.5 Sr0.5 Zn0.2 Fe0.8 O3−δ (BSZF), was investigated as a novel cathode material for intermediate-temperature solid-oxide fuel cells (IT-SOFCs). Room-temperature nonstoichiometry of BSZF was as high as 0.412, which was favorable for oxygen–reduction reaction. At 700°C, the polarization resistances were as low as 0.22 and 0.13 Ω·cm2 , respectively, for pure and impregnated BSZF cathodes under open-circuit conditions, suggesting that oxygen-deficient BSZF was a promising cathode candidate for IT-SOFCs. 相似文献