共查询到20条相似文献,搜索用时 15 毫秒
1.
Przybylski K. Brylewski T. Morawski A. Łada T. 《Journal of Thermal Analysis and Calorimetry》2001,65(2):391-398
The influence of Ba2Ca2Cu3Ox precursor on the synthesis and properties of (Hg,Pb)Ba2Ca2Cu3O8+δ has been examined. Fine homogeneous Hg-free precursor powder of Ba2Ca2Cu3Ox of desirable phase composition was prepared by sol-gel method using EDTA acid as a complexing agent. A reproducible superconducting
sample of Hg0.8Pb0.2Ba2Ca2Cu3O8+δ with fine-grained, dense microstructure, composed predominantly of (Hg,Pb)-1223 phase and with advantageous magnetic properties,
was synthesized by high pressure crystallization in mercury environment of well-calcined Ba2Ca2Cu3Ox precursor.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
2.
Z. Klencsár E. Kuzmann A. Vértes P. C. M. Gubbens A. M. van der Kraan M. Bódogh I. Kotsis 《Journal of Radioanalytical and Nuclear Chemistry》2000,246(1):113-115
151Eu and 141Pr Mössbauer spectroscopy was applied to study the effects of Pr substitution for Eu or Ba atoms in Eu1-x
Pr
x
Ba2Cu3O7- and EuBa2-x
Pr
x
Cu3O7-, respectively. It was found that there exists a correlation between the 151Eu isomer shift and the onset temperature of the superconducting transition, independent of the location of Pr. This shows that the extra electrons provided by the Pr increase the electronic density in the copper oxide planes and in the 4f orbitals of Eu31, simultaneously. The polycrystalline compound EuBa1.3Pr0.7Cu3O7- has been investigated by 141Pr Mössbauer spectroscopy. The observed 141Pr isomer shift, (4.2 K) = 0.10(15) mm/s relative to PrF3, reflects a valence state of 3+ for the Pr located at the Ba site in EuBa1.3Pr0.7Cu3O7-, being in contrast to the valence state of 3.4+ found earlier for Pr which was situated at the rare earth site. This means that the valence state of Pr substituted for Eu is different from that of Pr substituted for Ba. These results suggest that the suppression of superconductivity by Pr substituted for the rare earth atoms is a consequence of the hole filling effect. 相似文献
3.
Thermoanalytical Studies of Ga-substituted MBa2Cu3O7–δ Superconducting Compounds Formation (M=Yb,Eu)
A thermoanalytical study in non-isothermal conditions was realized on Ga-substituted MBa2Cu3O7-δ superconducting compounds formation (M=Yb, Eu). The presence of different oxides in the reaction mixtures leads to different reactivity of the system. The type
of lanthanoide ion present in the studied compositions determines the reactivity of the system. In the system containing Eu
the solid state reactions start at lower temperature than in the system containing Yb. Ga-substitution does not change evidently
the thermal behavior of the unsubstituted samples. Different reactivities of the studied reaction mixtures led, after similar
thermal treatment in isothermal conditions, to samples with different structure and superconducting properties.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
4.
Ko In-Yong Kim Na-Ri Lee Jin-Yeoung Park Na-Ra Doh Jung-Mann Shon In-Jin 《Research on Chemical Intermediates》2010,36(6-7):775-784
Nanopowders of Cu and Al2O3 were synthesized from 3CuO and 2Al powders by high-energy ball milling. Nanocrystalline Al2O3 reinforced composite was consolidated by pulsed-current activated sintering method within 2 min from mechanically synthesized powders of Al2O3 and Cu. The relative density of the composite was 96%. The average hardness and fracture toughness values obtained were 540 kg/mm2 and 6.3 MPa m1/2, respectively.
相似文献5.
NeutronDiffractionStudyonStructureofα-LiIO_3SingleCrystalunderDCVoltageChengYu-Fen;YangZhen;ChengZhi-Xu;GuoLi-Ping(ChinaInsti?.. 相似文献
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A. M. Pak O. I. Kartonozhkina G. T. Izdebskaya V. N. Ermolaev A. V. Koroiev 《Russian Chemical Bulletin》1993,42(7):1257-1259
The stereoselective hydrogenation of 2-hexyne in ethanol on Cu/-Al2O3 catalysts (1–40 % Cu) at 4–10 atm and 80–120 °C has been studied. The reaction affordscis-2-hexene as the only reaction product in 100 % yield at [Cu] 30 %. For samples with 20 % Cu, hydrogenation proceeds in parallel with absorption of H2 by the catalyst.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1314–1315, July, 1993. 相似文献
8.
The energetics, electronic structures, and optical properties of several neutral vacancies for γ-Si3N4 are studied based on density function theory within the generalized gradient approximation. The binding and formation energies of nitrogen vacancy are smaller than that of silicon vacancies, implying that nitrogen vacancy can be easily formed in γ-Si3N4.Corresponding density of states of different point vacancies is analyzed. We concluded that the neutral silicon vacancies introduce the p-type carriers into the system, whereas single nitrogen vacancy leads to an n-type semiconductor. The results show indirect semiconductor of nitrogen vacancy for γ-Si3N4. The effects of optical properties are discussed on single vacancies for γ-Si3N4. For silicon vacancies, the materials have much higher static dielectric constants than these of nitrogen vacancy and perfect γ-Si3N4. The single nitrogen vacancy for γ-Si3N4 has no effects on absorption and reflection in visible and infrared light. For silicon vacancy, it is significantly increased. 相似文献
9.
用电泳法在厚度为5 mm×10 mm×0.5 mm的YBa2Cu3O7-δ上沉积厚约70 μm的 La0.8Te0.2MnO3 形成La0.8Te0.2MnO3/YBa2Cu3O7-δ (F/S)双层结构. 通过扫描电子显微镜观察双层结构剖面的形貌, 采用标准的四引线法测量YBa2Cu3O7-δ层的电阻特性. 在F/S双层结构中通入1 mA的注入电流, 无论电流从S层流入F层( Iinj), 或者电流从F层流入S层(-Iinj), 正常电阻均比未加注入电流时的电阻低; 超导转变温度均比未加注入电流的转变温度高. 相似文献
10.
Maria Ochsenkühn-Petropulu Irene Vottea Rachel Argyropulu Leonidas Mendrinos Klaus-Michael Ochsenkühn 《Mikrochimica acta》1999,130(4):289-294
Coatings of the high-temperature superconductor YBa2Cu3O7–x (x = 0.1–0.2) (YBCO), were deposited on commercial Ni,Ti and stainless steel substrates, by an electrophoretic deposition technique. Sintering and annealing procedures were followed in order to get strongly adherent superconducting films. The suitability of the used substrates was tested by measuring the stoichiometry and the superconducting properties of the deposited coatings by X-ray diffraction analysis (XRD), Raman spectroscopy and magnetization measurements with a superconducting quantum interference device (SQUID). 相似文献
11.
Transition-metal doped double-perovskite structure oxides GdBaCo2/3Fe2/3Ni2/3O5+δ (FN-GBCO), GdBaCo2/3Fe2/3Cu2/3O5+δ (FC-GBCO), GdBaCoCuO5+δ (C-GBCO) and pristine GdBaCo2O5+δ (GBCO) were synthesized via a citrate combustion method. The thermal-expansion coefficient (TEC) and electrochemical performance of the oxides were investigated as potential cathodes for intermediate-temperature solid oxide fuel cells (IT-SOFCs). The TEC exhibited by the FC-GBCO cathode up to 900 °C is 14.6 × 10?6 °C?1, which is lower than the value of GBCO (19.9 × 10?6 °C?1). Area specific resistances (ASR) of 0.165 Ω cm2 at 700 °C and 0.048 Ω cm2 at 750 °C were achieved for the FC-GBCO cathode on a Ce0.9Gd0.1O1.95 (CGO) electrolyte. An electrolyte supported (300 μm thick) single-cell configuration of FC-GBCO/CGO/Ni-CGO attained a maximum power density of 435 mW cm?2 at 700 °C. The unique composition of GBCO co-doped with Fe and Cu ions in the Co sites exhibited reduced TEC and enhancement of electrochemical performance and good chemical compatibility with CGO, and this composition is proving to be a potential cathode for IT-SOFCs. 相似文献
12.
G. M. Kuz'micheva I. N. Afanas'eva Yu. V. Ésaulova I. E. Kostyleva E. P. Khlybov A. S. Andreenko 《Journal of Structural Chemistry》2002,43(5):809-827
The composition and structure of (M,Cu)(Sr,Ln)2(Ln,Ca,Sr)Cu2O8– phases, where M = B, Al, Cr, Pb, Bi, Ru, or Mo (1212 type), and (M,Cu)(Sr,Ln(2(Ln,Ce4+)2Cu2O10– phases, where M = V, Cr, Mn, Ru, or Mo (1222 type), have been determined. The role of the M cation in the formation of the crystal structures and the superconductivity phenomenon was analyzed. The relationship between the type of M cation and structural parameters was discovered. 相似文献
13.
Energetic heterogeneity of adsorbents is conditioned by the differences in topology of adsorption centres, dispersion of pore sizes and other factors. This paper describes theoretical and experimental studies that demonstrate a method for estimation of the energetic heterogeneity of adsorbents by making use of the results from single thermogravimetry Q-TG and Q-DTG curves, recorded under quasi-equilibrium conditions, for preadsorbed liquid on a porous solid surface.This revised version was published online in November 2005 with corrections to the Cover Date. 相似文献
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During the heating of YBCO a peritectic reaction takes place at 1020C, which can be described by: 2YBa2Cu3O7–xY2BaCuO5+L+(1-2x)/2O2 (1) whereL = 3BaCuO2 +2CuO is a fluid with limited amount of yttrium.It has been reported, that many parameters can influence the reaction. From one side not only the starting size of grains but also the heating rate have an influence on the resulting Y2BaCuO5-phase. From the other side, there is a change of the peritectical temperature caused by changing of the partial pressure of O2 and the presence of parasitic phase.From general kinetic consideration one can draw the conclusion, that different mechanisms (nucleation, phase-boundary reaction and diffusion) can control the reaction.Using DTA/TG measurements, the peritectic reaction has been examined. Classical kinetic methods (Kissinger and Friedman) has been used. The Friedman method has given the dependence of the activation energy from reaction degree. This suggests many steps reactions. The dependence of the DTA-peaks from the heat rate suggest a parallel steps of reaction. This assumption can be motivated by evaluation of free O2, one solid and liquid phase formation. Amount of this phases depends on the heating rate. Additionally X-ray and microscopic methods has been used. In this way was shown, that the perovskit structure is stable up to peritectical temperature and than is dramatically destroyed. From microscopic observations has been got information about shape and size of solid phase and it's creation as a function of temperature, time and starting grain size.
Die Arbeit wurde BMBF gefördert und durch Land NRW unterschtützt. 相似文献
18.
《Spectrochimica Acta Part B: Atomic Spectroscopy》1988,43(8):951-954
X-ray photoelectron spectroscopy (XPS) or electron spectroscopy for chemical analysis (ESCA) has been employed to investigate the chemical nature and the electronic structure of the YBa2Cu3O7−x system at different stages of preparation. The binding energy measurements showed that O 1s, Ba 3d and Y 3d core levels undergo appreciable changes during the firing and subsequent heat treatment. The chemical shift in O 1s is believed to be due to a higher concentration of holes in the superconductor phase. No indication for the existence of a monovalent Cu(I) species was found at any stage of preparation. 相似文献
19.
G. V. Rama Rao U. V. Varadaraju S. Venkadesan S. L. Mannan 《Journal of Thermal Analysis and Calorimetry》1997,48(5):1051-1067
The high temperature superconducting compound YBa2Cu3O72212; (Y-123) is synthesised by sol-gel process using various precursors viz., acetate, acetate-citrate, nitrate-citrate and acrylamide. The phase purity of the final product depends on the homogeneity of the gels which intern depends on the bonding of the metal ions in the gels. The samples prepared by acrylamide and nitrate-citrate gel routes yielded phase pure Y-123 compound with better superconducting properties. The mechanism of formation of Y-123 in all these four gel routes is established by characterising the gels and intermediate phases using TG, DTA and XRD techniques. Kinetic analysis is carried out on the mass loss data using the method proposed by Phadni's and Deshpande. Avrami-Erofeev nuclei growth in case of acrylamide, diffusion controlled process in nitrate-citrate and phase boundary reaction mechanisms in case of acetate-citrate gels are found to be responsible for the formation of Y-123 phase.The authors are grateful to Dr. Baldev Raj, Director, Metals and Materials Group, for his constant encouragement and support. We thank Prof. G. V. Subba Rao, Director, Central Electrochemical Research Institute, Karaikudi for his keen interest in this work. Thanks are also due to Dr. Sundaram, CECRI, Karaikudi for his help in thermal analysis experiments. 相似文献
20.
J. Liu H. Xu W. Shen X. Pan Y. Xiang 《Journal of Thermal Analysis and Calorimetry》1999,58(2):309-315
Mn2O3/-Al2O3 catalysts were prepared by the impregnation method, and the maximum monolayer dispersion capacity or dispersion threshold value of Mn2O3 on the surface of -Al2O3 was determined to be 13.08% from the decomposition mass loss of supported Mn(NO3)2 in the monolayer state. This was compared with the values estimated from a close-packed monolayer model and an interaction model. It was confirmed that the high activities and selectivities of the catalysts for benzoic acid hydrogenation to benzaldehyde are due to the monolayer dispersion of the Mn2O3 on the surface of -Al2O3.This revised version was published online in November 2005 with corrections to the Cover Date. 相似文献