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用固相反应法合成了名义组分为Bi1.92Pb0.32Sr2Ca1.7Mg0.3Cu3.07Ox的块状样品。X射线衍射谱(XRD)、扫描电子显微镜(SEM)和电子探计X射线分析(EDAX)结果以及块状和粉状试样的交流磁化率测量表明,样品中存在110和85K两个超导相;2223相(110K)首先在2212相(85K)晶体的晶界和外部区域生成。本文认为,最初存
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采用固相反应法合成了名义组份为Bi2-xPbxSr2Ca2Cu3Oy (x=0.30;0.35;0.40;0.45)的样品。对样品进行了物相和结构分析,同时测量了电阻-温度关系和直流磁化率。结果表明:x=0.35的样品为单相材料,X射线相分析和电子衍射表明其相结构类似2223相,为四方结构,其晶格常数为a=b=5.414?,c=37.106?,且沿a,b两个方向都观察到调制结构。电阻和直流磁化率测量结果显示:在温度高于50K以上,仅存在一个107K超导相。此外,单相材料的制备条件(组分、烧结温度、室温下淬火及淬火速率)非常苛刻。如同1-2-3相材料一样,氧含量不仅影响样品的成相规律、零电阻温度,而且还严重影响其正常态的输运性质。
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《Superlattices and Microstructures》1999,25(3):527-531
In order to elucidate the formation mechanism of the Bi, Pb(2223) phase, extensive investigations have been performed by means of combined differential thermal analysis and thermo-gravimetric measurements, X-ray diffraction as well as scanning electron microscopy and energy dispersive X-ray microanalysis.Starting from co-precipitated oxalate powders, the transformations leading to the formation of the Bi, Pb(2223) phase were studied. Based on these investigations the Bi, Pb(2223) phase formation process, involving the Bi, Pb(2212), Ca2PbO4and alkaline-earth cuprate phases as precursors has been separated into elemental steps. A new model for the formation mechanism of the Bi, Pb(2223) phase will be presented.The Bi, Pb(2223) phase formation kinetics has been studied using the Avrami relation for isothermal phase transformations. The analysis of the Bi, Pb(2223) phase evolution revealed a marked change of the Avrami exponent during the course of the Bi, Pb(2223) phase formation after about 12 hours sintering at 857 ° C.The activation energy for the formation of the Bi, Pb(2223) phase has been determined under various experimental conditions. The nominal composition of the precursor powders, the temperature at which they were calcined as well as the size of their constituents were found to have a significant influence on the value of the activation energy. 相似文献
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The Ag/Tl2Ba2Ca2Cu3O10/CdSe heterostructure was fabricated at room temperature by soft electrochemical processing technique for the first time. The formation of the heterostructure with non-diffusive interfaces was confirmed by X-ray diffraction. The crystallite sizes determined for Tl-2223 and CdSe films were 33 nm and 25 nm, respectively. The Tl2Ba2Ca2Cu3O10 film electrodeposited onto Ag-substrate has shown the superconducting transition temperature Tc at 116.5 K and Jc = 2.1 × 103 A/cm2. These values were found to improve after the deposition of CdSe onto Ag/Tl-2223 films. The effect of red He-Ne laser irradiation on the superconducting properties of heterostructure are studied and discussed at length in this paper. 相似文献
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Avrami’s equation was found to be the best kinetics theory to describe the high-Tc Bi-2223 crystal formation so far. There are three parameters (exponential index n, activation energy E and parameter k) in the equation. A series of research works have been done on the determination of parameters n and E, but few on another parameter k are to be found. The purpose of the approach was to determine and study the role of k in the formation of Bi-2223 crystals. The analysis in the research showed that the parameter k could describe the exhausting speed of reactants, and determine reaction probability and mean lifetime of reactants. The growth mechanism of the 2223 polycrystals was found to show some differences from the prediction of the Avrami’s theory model. At the initial duration, the 2223 crystal growth was much lower than the theoretical prediction; especially there was a mature duration to be found at the last growth duration, at which the 2223 crystal almost did not increase, but its crystal grains obviously became larger. This was a typical morphological transformation. The morphological transformation was the first time to be reported for the growth of the 2223 phase. 相似文献
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Lin Zhu Jining HeDianran Yan Yanchun DongJianxin Zhang Xiangzhi LiHanlin Liao 《Applied Surface Science》2011,257(23):10282-10288
In the present study, Fe-Al2O3-FeAl2O4 composite coatings were successfully deposited by reactive plasma sprayed Al/Fe2O3 agglomerated powder. Phase composition and microstructure of the coatings were determined by XRD and SEM. The results indicated that the composite coatings were principally composed of three different phases, i.e. FeAl2O4 phase as main framework, dispersed ball-like Fe-rich phase, and small splats of Al2O3 phase, and it was thought that the in situ synthesized metal phase was helpful to toughen the coating matrix. According to the results of the indentation and frictional wear tests, the composite coating exhibited excellent toughness and anti-friction properties in comparison with conventional Al2O3 monophase coating, though its microhardness value was a little lower than that of Al2O3 coating. The formation mechanism and the toughening mechanism of the composite coating were clarified in detail. 相似文献
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《Physica C: Superconductivity and its Applications》2002,360(1-2):55-58
Reactivity of several oxide materials (OM) with BSCCO powder and oxygen diffusion through OM layer has been tested at temperature ≈840 °C in air. The OM (e.g.: BaZrO3, SrCO3, MgO and ZrO2) showing the low or no reactivity with BSCCO have been mixed (10 wt.%) with precursor powder and used for single-core tapes. Bi-2223/Ag/OM/Ag single-core tapes with oxide barriers made of BaZrO3, SrCO3, ZrO2 and Al2O3 have been also prepared by a standard powder-in-tube technique. The used OM in the direct contact with BSCCO influences the electrical properties of Bi-2223 phase differently. These is because the oxides react with BSCCO during the heat treatment and simultaneously affect the 2212→2223 phase transformation, the Bi-2223 grain growth and so also grain connectivity. SrCO3 powder has been evaluated as the best material from the point of no destructive effect on 2223 phase transport current property. The oxide barrier controls the oxygen diffusion during the tape heat treatment and simultaneously the HTS phase formation kinetics, its purity and content within the superconducting core. For single-core Bi-2223/Ag/OM/Ag tapes, the highest current density was measured for Al2O3 due to only slightly reduced oxygen diffusion through the barrier. 相似文献
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Infrared and Raman spectra of polycrystalline H3OUO2PO4·3 H2O (HUP) and its D and P18O4 derivatives, in the form of dense transparent disks and wet powder, have been investigated at various temperatures in the 100–300 K region. The bands due to framework vibrations are similar to those of KUP, whereas those for the protonic species are different. OH stretching and bending bands of the oxonium ion have been identified at 2920, 1740 and 1160 cm?1 in the low-temperature spectrum of HUP. Differential scanning calorimetry (DSC) and infrared (IR) intensity investigations show a phase transition between 274 and 260 K. The mechanism of the phase transition consists, as in the case of KUP, of ordering of the protonic species, which induces ordering of PO4 tetrahedra. The ordering can be influenced by excess water content, stacking faults and stress (ferroelastic behaviour is evidenced). The conductivity mechanism in HUP is discussed. 相似文献
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The DC and AC behaviour of Ag-sheathed Bi2Sr2Ca2Cu3Ox(BSCCO-2223) tapes, arranged in a z-stack configuration, are investigated. The number of tapes in the stack can be varied, from one (single tape) to four, as well as the inter-tape separation. Tapes are isolated and connected in series to ensure a uniform current distribution among the tapes. The critical currents and the average AC losses per tape as a function of the transport current are measured. By increasing the number of tapes or/and reducing the separation between them, the critical current of each tape is decreased while the average losses are increased. Tapes in a stack are found to be electromagnetically coupled, the degree of this coupling being dependent on the separation among them. Theoretical models are provided to explain the experimental results. 相似文献
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W.J. Yu Zh.Q. Mao Sh.J. Feng M.L. Tian G.E. Zhou Y.H. Zhang 《Physica C: Superconductivity and its Applications》1994,230(3-4):323-326
A new phase of Ba2(Cu0.7Cd0.3)O3 has been discovered. The composition of the phase was examined by energy dispersive X-ray spectrometry. The phase exhibits a tetragonal structure with lattice constants a=4.077 Å and c=7.970 Å, and its space group is P4/mmm. We propose a double-center-perovskite structure model, which is similar to that of (Ba, Sr)2CuO2(CO3) [1, 2]. The simulated XRD is close to the observed one. The analysis results of elemental analyzer and Fourier transform infrared spectrometer reveal that the phase does not contain CO
. The cuprate is an insulator, but its new cell structure and the large size of the CuO2 planes seem to suggest a good reason for researching new superconductors. The roles of CdO in the solid state reaction and the formation of the new phase are discussed. 相似文献
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Nanlin Wang Qirui Zhang Yugui Wang Mingrong Ji Xianming Liu 《Zeitschrift für Physik B Condensed Matter》1992,86(3):325-328
The electronic structure of Bi-based 2223 single phase superconductor has been studied by ultraviolet and X-ray photoemission. By comparison with that of 2212 phase superconductor, we find a higher density of states nearE
F
for 2223 phase. From analysis of the Cu 2p core-level spectroscopy, we obtain a relatively smaller charge transfer energy between copper and oxygen as well as the Coulomb repulsion energy on Cu site for 2223 phase. We relate these changes to the increase of hole concentration from 2212 to 2223 phase. The experimental results support the viewpoint that the transition temperature should be correlated with the density of states atE
F
. 相似文献
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Using a density functional approach calculation, the structural, energetic and electronic properties of Mg2Ni phase as well as its high/low temperature (HT/LT)-Mg2NiH4 complex hydrides are systematically investigated. The optimized structural parameters including lattice constants and atomic positions are very close to the experimental data determined from X-ray and neutron powder diffraction. A detailed study of the electronic structures including the energy band, density of states (DOS) and charge density distribution reveals the orbital hybridization and characteristics of bonding orbits within Mg2Ni and its hydrides. Based on the calculated results of the reaction heat of hydrogenation, enthalpy of formation and energy cost to remove H atoms, it is found that the formation ability of LT-Mg2NiH4 is higher than that of the HT phase during the hydrogenation of Mg2Ni alloy; moreover, LT-Mg2NiH4 has a relatively higher structural stability than HT phase, which is also well explained through the DOS and the charge distributions of HT/LT-Mg2NiH4 phases. 相似文献
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Vladimir Dmitriev Vitaly Sinitsyn Denis Machon Eugeny Ponyatovsky Hans Peter Weber 《Journal of Physics and Chemistry of Solids》2003,64(2):307-312
The effect of pressure on the phase transformations in Sm2(MoO4)3, Gd2(MoO4)3 and Eu2(MoO4)3 crystals has been studied in situ using synchrotron radiation. All three isostructural compounds undergo a structural phase transition at 2.2-2.8 GPa to a new phase, which is interpreted as a possible precursor of amorphization. Amorphization in these crystals occurs irreversibly over a wide pressure range, and its mechanism, interpreted as a chemical decomposition, is found to be weakly affected by the degree of hydrostaticity. 相似文献
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N. Petit V. Garnier V. Ta Phuoc R. Caillard A.-M. Frelin A. Ruyter I. Laffez J.-C. Soret A. Maignan F. Gervais 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,25(4):423-429
The reflectivity spectra of an oriented ceramic of Bi-2223 has been investigated by polarized infrared reflectivity spectroscopy
in the energy range 0.005-2.2 eV. It is shown that the data for the polarization parallel to the c axis cannot be fitted with a one-component Drude or extended-Drude model. The conductivity spectrum is then obtained from
the best fit of a “double-damping Drude” model to reflectivity spectra, itself derived from the factorized form of the dielectric
function, and by a Kramers-Kronig inversion as well. The data and their analysis give a new insight of the 2D character of
the system.
Received 26 April 2001 and Received in final form 28 August 2001 相似文献