共查询到20条相似文献,搜索用时 31 毫秒
1.
Teen-Hang Meen Ying-Chung Chen Ken-Whie Liaw Hung-Duen Yang 《Journal of the American Ceramic Society》1993,76(8):1948-1952
X-ray diffraction patterns show that most samples of Y1-x Prx Ba2 Cu4 O8 examined in the present study contained a single YBa2 Cu4 O8 (1-2-4) superconductive phase for x<0.7.Lattice parameters a and b increased with Pr concentration, suggesting that most of the Pr is trivalent in Y1-x Prx- Ba2 Cu4 O8 . The zero-resistance temperature, T co , decreases monotonically from 80 K at x=0 to 12 K at x=0.65, and superconducting transition widths tend to broaden for x>0. The room-temperature resistivity changes linearly until x=0.7 and increases abruptly at x=-0.75. The critical concentration, xcr , thus was estimated to be 0.7. The effective magnetic moments of Pr in Y 1-x Prx Ba2 Cu4 O8 were 3.63., 3.35, and 3.23, μB for x=0.2, 0.4 and 0.6, respectively. In the R0.8 Pr0.2 Ba2 Cu4 O8 system, the depression of Tc weakly depends on the ionic radius of rare-earth elements. Similarities and differences between Y 1-x Prx Ba2 Cu4 O8 and Y1-x Prx- Ba2 Cu3 O7-y also were noted and are discussed in this paper. 相似文献
2.
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
3.
Anurag Dwivedi Mark A. Rodriguez Alastair N. Cormack 《Journal of the American Ceramic Society》1992,75(7):1993-1996
Compositions of La1- x Ba x CuO3 , where x ranges from 0.0 to 0.5, were fired in air, oxygen-enriched air, and oxygen. Studies show that BaO cannot make a solid solution with LaCuO3 without changing the basic structure. The resulting phases, in all attempts, were the binary compounds La2 CuO4 , La1- x Ba x CuO3-δ ( x = 0.2 to 0.5), or their mixtures. All samples showed metallic conductivity. Extra oxygen in the reaction atmosphere appeared to encourage the formation of the LaCuO3 -based phases of La1- x Ba x CuO3-δ ( x = 0.2 or 0.5). We provide a defect-chemical and thermodynamical explanation for this observation. 相似文献
4.
Takayuki Komatsu Michiko Ueta Tomohiro Ohki Ryuji Sato Kazumasa Matusita 《Journal of the American Ceramic Society》1992,75(7):1864-1869
The Ba-doped superconducting (Bi,Pb)2 Sr2- x Ba x Ca2 Cu3 O y and (Bi,Pb)2 Sr2 Ca2- x Ba x Cu3 O y (0 ≦ x ≦ 1.0) were prepared by using a melt-quenching method, and the effect of Ba additions on the glass-forming ability and the crystalline phase was examined. The glass-forming ability was not improved by substitution of Ba for Sr or Ca, and particularly BaPbO3 as well as CaO was observed in the melt-quenched sample of (Bi,Pb)2 SrBaCa2 Cu3 O y . BaPbO3 crystals were precipitated in all glass-ceramics with Ba substituted for Sr or Ca. The partial substitution of Ba substituted for Sr was effective for the formation of the high- T c phase, and (Bi,Pb)2 Sr1.4 Ba0.6 Ca2 Cu3 O y glass-ceramics obtained by annealing at 830°C for 100 h exhibited superconductivity with a T c of 103 K, although BaPbO3 and the low- T c phase were still largely present. 相似文献
5.
Asok K. Sarkar Lval O. Salyer Binod Kumar 《Journal of the American Ceramic Society》1989,72(7):1247-1248
A technique for preparing Y1 , Ba2 Cu3 O7-x /polymer composites showing superconducting resistive transition above liquid-nitrogen temperature has been developed. A sintered Y1 Ba2 Cu3 O7-x disk was impregnated with a low-viscosity 2-ethylhexyl acrylate monomer containing benzoyl peroxide and dicumyl peroxide as polymerization catalysts. The impregnation of sintered disks was carried out under moderate vacuum for 30 min followed by an overnight soaking. The polymerization treatment consisted of a heat treatment at 60°C for 24 h followed by a second heat treatment at 80°C for 8 to 10 h. The superconductorlpo1ymer specimens exhibited superconducting resistive transition at ≃80 K. The scanning electron micrograph reveals excellent welting, infiltration, and polymerization of the monomer into the superconducting material. 相似文献
6.
Gilles Bussod Alexander Pechenik Chung-tse Chu Bruce Dunn 《Journal of the American Ceramic Society》1989,72(1):137-139
The knowledge of the steady-state stress for plastic deformation as a function of temperature and strain rate is essential for hot-forming superconducting material into commercially useful shapes. In this paper, results are presented on the experimental determination of the rheology of fully dense polycrystalline Y1 Ba2 Cu3 O7−x superconducting material at temperatures ranging from 750° to 950°C and strain rates of 10−4 , 10−5 , and 10−6 s−1 . The data are best fitted by a power law: ε(s−1 )=8.9 × 10−17 . (s−1 ) σ2.5 (Pa) exp [−2.01 × 105 (J·mol−1 )|RT]. X-ray analysis shows that the superconducting material retains its phase composition after nearly 70% total strain of the sample. A strong anisotropy in the resistivity of the deformed samples is observed because of the development of a preferred orientation of the a or b axis of Y1 Ba2 Cu3 O7−x orthorhombic perovskite single crystals perpendicular to the principal maximum compressive stress. 相似文献
7.
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
8.
Katharine-G. Frase E. G. Liniger David R. Clarke 《Journal of the American Ceramic Society》1987,70(9):204-C
We report the compatibility relationships between compounds, including the newly discovered superconducting Y1 Ba2 Cu3 Ox phase, in the Y2 O3 -BaO-CuO system at 950°C. In addition to the previously reported ternary compounds, there is a new compound with a composition Yl Ba3 Cu2 Ox . The new compound is a perovskite 'space group P4mm) with lattice parameters a =4.078 Å (0.4078 nm) and c =4.01 Å (0.401 nm). There are also at least two structurally distinguishable binary phases between barium oxide and the known BaCuO2 , but they appear to be hygroscopic and are beyond our current capabilities of analysis. 相似文献
9.
Peter J. Majewski Arthur Jalowicki Stefanie Kaesche Fritz Aldinger 《Journal of the American Ceramic Society》2001,84(1):183-187
The phase relations within the system Tl2 O3 –BaO–CaO–CuO including Ag have been studied with emphasis on the high-temperature superconducting phases TlBa2 Ca2 Cu3 O8.5 (1223 phase), Tl2 Ba2 Ca2 Cu3 O10 (2223 phase), TlBa2 CaCu2 O6.5 (1212 phase), and Tl2 Ba2 CaCu2 O8 (2212 phase) at 890°C in an oxygen atmosphere. 1223 has been found to be in equilibrium with a liquid phase that is Tl poor. 2223 and 2212 exhibit varying Tl/(Ba + Ca) ratios. The three-phase field 1223 + 2223 + 2212 has been identified. The results of this study emphasize that multiphase samples can be prepared which consist of three superconducting phases, each exhibiting a critical temperature of 100 K or above. 相似文献
10.
Asha Mary John Rajan Jose Jose Kurian Poo Koodan Sajith Jacob Koshy 《Journal of the American Ceramic Society》1999,82(6):1421-1424
A new group of complex perovskites Ba2 REHfO5.5 (where RE = La, Pr, Nd, and Eu) has been synthesized and sintered as single-phase materials with high sintered density and stability using a solid-state reaction method for the first time. The structure of Ba2 REHfO5.5 has been studied by X-ray diffactometry (XRD) and all of the perovskites are isostructural and have a cubic structure. The dielectric constant and loss factor values of these materials are in a range suitable for their use as substrates for YBa2 Cu3 O7-delta superconductors. XRD and resistivity measurements show that there is no detectable reaction between YBa2 Cu3 O7-delta and Ba2 REHfO5.5 , even when the two substances are mixed thoroughly and sintered at 950°C for 15 h. The addition of Ba2 REHfO5.5 up to 20 vol% in YBa2 Cu3 O7-delta -Ba2 REHfO5.5 composite shows no detrimental effect on the superconducting transition temperature of YBa2 Cu3 O7-delta . Thick films of YBa2 Cu3 O7-delta fabricated on polycrystalline Ba2 REHfO5.5 substrate have a superconducting zero resistivity transition of 92 K, indicating the suitability of these new materials as substrates for YBa2 Cu3 O7-delta films. 相似文献
11.
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
12.
Subsolidus phase relations in the La2 O3 –BaO–CuO system were studied at 950°C. Three previously reported binary compounds exist (La2 CuO4 , BaLa2 O4 , and BaCuO2 ) and five previously reported ternary phases occur (La2-x Bax CuO4-(x/2)+δ , La4-2x Ba2+2x Cu2-x O10-2x , La2-x Ba1+x Cu2 O6-(x-2) , La3-x Ba3+x Cu6 O14±δ , and La4 BaCu5 O13+δ ). Of the seven phases in the diagram, all but BaLa2 O4 , BaCuO2 , and La4 BaCu5 O13+δ were shown to exhibit significant ranges of solubility. The diagram is important in that both >30 K (La2-x Bax CuO4-(x/2)+δ ) and >90 K (La3-x Ba3+x Cu6 O14+δ , x=1) superconductors occur. 相似文献
13.
Chung-Yi Tsai Anthony G. Dixon Yi Hua Ma William R. Moser Marina R. Pascucci 《Journal of the American Ceramic Society》1998,81(6):1437-1444
La1- x A' x Fe0.8 Co0.2 O3-δ (A'= Ca, Sr, Ba) perovskite powders were synthesized to attain the desired properties of high O2 flux and stability under reducing conditions. Steady-state oxygen permeation rates for La1- x A' x Fe0.8 -Co0.2 O3-δ perovskite membranes in nonreacting experiments with air on one side and helium on the other side of the membrane were in the order A' x = Ba0.8 > Ba0.6 > Ca0.6 > Sr0.6 . Partial oxidation of methane to syngas (CO + H2 ) was performed in a dense La0.2 Ba0.8 Fe0.8 Co0.2 O3-δ membrane reactor at 850°C in which oxygen was separated from air and simultaneously fed into the methane stream. The reducing atmosphere affected the membrane reaction-side surface while barium enrichment occurred on the air-side surface. Oxygen continuously transported from the air side appeared to stabilize the membrane interior, and the reactor was operated for up to 850 h. 相似文献
14.
Hee-Gyoun Lee Jong-Hyun Park Jin-Tae Song 《Journal of the American Ceramic Society》1995,78(7):1980-1982
Effects of melt chemistry and platinum doping in the refinement of Y2 Ba1 Cu1 Oy (211) particles were investigated for the system Y-Ba-Cu-O. The shapes of the 211 particles in the present study changed from needlelike in a (CuO + BaCuO) melt to nearly spherical in a CuO melt. Platinum plays a small role in the growth inhibition of 211 particles. Barium atoms clearly had no effect on the role of Pt in refining 211 particles, and Pt was found to affect the refinement as an elementary atom rather than as part of a Pt-related compound. The main role of Pt in the refinement process for the system Y-Ba-Cu-O seems to lie in changing the interfacial energy of the 211 particles . 相似文献
15.
Won-Hyuk Lee Yoshihiro Abe Eikichi Inukai 《Journal of the American Ceramic Society》1993,76(4):849-856
Ag2 O-doped superconducting Bi2 Sr2 Ca1 Cu2 O x ceramics were prepared by a melt-quenching–reheating method. It is found that the Ag2 O-doped, as-cast specimens exhibit superconductivity ( T c = around 80 K) by heat treatment at temperatures around 800°C even in an evacuated and sealed silica glass tube, while the undoped specimens do not and vaporize by the corresponding heat treatment. Conversion of the Ag2 O-doped, as-cast specimens into superconducting ceramics when heated in an evacuated vessel is explained in terms of the oxygen donor of Ag2 O in the specimen. This finding enables us to fabricate a desired shape of superconducting Bi2 Sr2 Ca1 Cu2 O x ceramics sealed in metals or glasses. The addition of Ag2 O to Bi2 Sr2 Ca1 Cu2 O x melt, however, had deleterious influences on the superconducting properties ( T c and J c ) of the resultant ceramics when obtained by heat treatment in air. 相似文献
16.
The stability of the (Bi,Pb)2 Sr2 Ca2 Cu3 O10±δ -type compound has been evaluated under conditions of elevated temperature (500°-860°C) and elevated oxygen fugacity (i.e., in O2 /Ar gas mixtures containing ≤120% O2 , at total pressures of 5207 MPa). At sufficiently high oxygen fugacities and temperatures, the (Bi,Pb)2 Sr2 Ca2 Cu3 O10±δ -type compound transformed into a mixture of a strontium-rich (Bi,Pb)1 -(Sr,Ca,Cu)2 Oy -type compound, a calcium-rich (Bi,Pb)2 -(Sr,Ca,Cu)2 Oy -type compound, CuO, and a small amount of (Sr,Ca)O. The decomposition of the (Bi,Pb)2 Sr2 Ca2 -Cu3 O10±δ -type compound was accompanied by a 2%-3% weight gain, which was consistent with an oxidation reaction. The conditions of oxygen fugacity and temperature leading to decomposition, and the resulting decomposition products, are compared for the (Bi,Pb)2 Sr2 Ca2 Cu2 O10±δ -type and Bi2 Sr2 Ca1 Cu2 O8±Ψ -type compounds. 相似文献
17.
Jacob Koshy Krishnan Sudarsana Kumar Jose Kurian Yogendra P. Yadava Alaatoor D. Damodaran 《Journal of the American Ceramic Society》1995,78(11):3088-3092
A new group of complex perovskites, REBa2 SnO5.5 (where RE = Pr, Sm, Eu, and Gd) have been synthesized and sintered as single-phase materials with high sintered density and stability by the solid-state reaction method. The structure of REBa2 SnO5.5 was studied by the X-ray diffraction technique, and all of them were found to be isostructural and have a cubic perovskite structure. The dielectric constant and loss factor values of these materials are in a range suitable for substrate applications. The X-ray diffraction and resistivity measurements have shown that there is no detectable reaction between YBa2 Cu3 O7-δ and REBa2 SnO5.5 , even when the substances are mixed thoroughly and sintered at 950°C for 15 h. Thick films of YBa2 Cu3 O7-δ fabricated on polycrystalline REBa2 SnO5.5 substrates gave superconducting zero resistivity transition T C(0) = 92 K, indicating the suitability of these new materials as substrates for YBa2 Cu3 O7-δ films. 相似文献
18.
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
19.
Steven P. Simner Michael D. Anderson Jeffry W. Stevenson 《Journal of the American Ceramic Society》2004,87(8):1471-1476
(La0.8 Sr0.2 )0.98 Fe0.98 Cu0.02 O3−δ can be sintered directly onto YSZ (without the need for a protective ceria interlayer). Though subject to an extended "burn-in" period (∼200 h), anode-supported YSZ cells using the Cu-doped LSF achieve power densities ranging from 1.3 to 1.7 W/cm2 at 750°C and 0.7 V. These cells have also demonstrated 500 h of stable performance. The results are somewhat surprising given that XRD indicates an interaction between (La0.8 Sr0.2 )0.98 Fe0.98 -Cu0.02 O3−δ and YSZ resulting in the formation of strontium zirconate and/or monoclinic zirconia. The amount and type of reaction product was found to be dependent on cathode and electrolyte powder precalcination temperatures. 相似文献
20.
Yang Gong-An Pu Yong-Ping Wang Jin-Fei Chen Xiao-Long Zhuang Yong-Yong 《Journal of the American Ceramic Society》2009,92(8):1891-1894
The influence of La2 O3 doped on the microstructure and dielectric properties, including the phase structure, temperature dependence of permittivity, and the hysteresis loop of BaTiO3 –Nb2 O5 –Fe2 O3 (BTNF) materials has been investigated in X-ray diffraction, SEM, and LCR analyzer, respectively. Experiments revealed that incorporation of proper content of La2 O3 basically soluted in the lattice of BaTiO3 and can control the grain-growth, reduce the dielectric loss of the BTNF materials. The development of microstructure promoted by the additives can result in the improvement of the dielectric constant. When the doping concentration of La2 O3 was 3.846 wt%, the relative dielectric constant of the sample sintered at 1280°C only for 2 h could reach 4308, and improve the dielectric-temperature characteristics markedly. As a result, a novel Y5P can be achieved in the BTNF ceramics, which is very promising for practical use in Y5P multilayer ceramic capacitors. 相似文献