Neutron and X-ray investigations on the oxygen bonding in YBa2Cu3O7-x combined with physico-chemical methods

The occupancy of the oxygen lattice positions at different annealing conditions in YBa₂Cu₃O_(7–x) were determined by Rietveld refinements using neutron and X-ray diffraction data. The occupation density for the oxygen positions O1 to O4 were ascertained. The values of the oxygen content of the samples from this method were compared with those measured by thermoanalysis. The O1 and O4 oxygen atoms are exchangeable by thermal treatment. The oxygen in the planes is fixed and can not be removed by thermal treatment up to 935°C. The binding strength of O1 in the lattice is stronger than that of O4 atoms; this is demonstrated by a higher temperature of dissociation of the O1 atoms. The amount of the oxygen taken up is not exactly equal to the oxygen actually in the lattice positions. In the temperature region below 400°C adsorption and chemisorption processes are become dominant.     

Chemical bonding in high-temperature YBa2Cu3O7 superconductors

Calculations for clusters serving as models for the electronic structure of the copper, barium, and oxygen sites in high-temperature YBa₂Cu₃O₇ superconductors were carried out in the framework of the discrete variation method. An analysis of the bond orders in such compounds was carried out using the overlap occupancies of various AO of the metal and oxygen atoms. Values were obtained for AO occupancies and effective charges on the atoms in the clusters.Institute of Chemistry, Urals Branch, Academy of Sciences of the USSR. Translated from Zhurnal Strukturnoi Khimii, Vol. 30, No. 5, pp. 12–16, September–October, 1989.     

YBa2Cu3O7-x涂层导体的研究进展

以YBa2Cu3O7-2（YBCO）超导涂层为导体的第二代高温超导带材由于其优异的本征性能，吸引着科学家不断探索和研究其实用成材技术。近年来，百米级长带的研制成功，使其成为当前国际上超导研究的热点。综述了近年来二代超导带材的发展状况，并对在镍和镍合金基带上制备涂层导体的工艺技术以及其基本结构特征做了较为系统的介绍，包括基带的制备技术、隔离层的生长、化学法和物理气相沉积法生长YBCO等。     

YBa2Cu3O7-x高温超导涂层导体磁通钉扎的研究进展

以YBa2Cu3O7-x(YBCO)超导涂层为导体的第二代高温超导带材由于其优异的本征性能,吸引着人们不断探索和研究其实用成材技术.现在,近千米长带的研制成功,使其已经或即将应用于电缆、马达和其他电力器件.为了更好地使YBCO涂层导体能够在高温高磁场下应用.最近在YBCO中引入钉扎中心以提高它的电磁性能的研究是一个热点.综述了近年来二代超导带材的发展状况,并对目前高温超导体中提高电学性能的研究做了较为系统的介绍.     

Order-disorder in YBa2Cu3O7

We summarize here results of a fairly detailed study by high-resolution electron microscopy and electron diffraction of the high-temperature superconductor YBa₂Cu₃O_7−δ. Data from the perfect structure for (100), (110), and (001) zones indicate that the material has an oxygen-deficient perovskite structure as previously reported from X-ray and neutron diffraction studies. In some cases planar defects along (001) directions were observed. A more important observation is the existence of a phase with disorder of the Y and Ba ion positions and of an additional amorphous phase. The perfectly ordered (defect-free) phase grows from the disordered material, and the planar defects are probably due to mechanical deformation during preparation of the material. These defects probably are not related to the superconducting properties, as recently suggested. The conclusions are consistent with the commonly encountered problems in the preparation of superconductors in high yields.     

Thermal neutron effect on YBa2Cu3O7

High-Tc superconductor YBa₂Cu₃O₇ was irradiated by thermal neutrons. Significant effects on the critical temperature were found. The changes were also investigated by X-ray diffraction technique.⁶⁵Cu (n, )⁶⁶Cu was the only reason for the degradation in superconducting properties. The existence of an isotope effect is argued.     

ChemInform Abstract: Melting and Resolidification of YBa2Cu3O7-x/Silver Composites.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.     

SC-MEH-MO calculations on high Tc superconductors. 1: The YBa2Cu8O cluster in YBa2Cu3O7

SC-MEH-MO calculations have been carried out on select clusters of the YBa₂Cu₃O₇ lattice structure. The results of an earlier computation on small CuO clusters are presented for comparison with the finding obtained on a YBa₂Cu₈O₂₆⁺ extended cluster. In the latter, the antiferromagnetic coupling of singularly occupied Cu and O levels is analyzed.     

The composition analysis of YBa2Cu3O7-δ or PrBa2Cu3O7-δ thin films and (YBa2Cu3O7-δ/PrBa2Cu3O7-δ)n heterostructures prepared by CVD

Some YBa₂Cu₃O_7-δ films and heterostructures prepared by Chemical Vapor Deposition (CVD) were analyzed in our laboratories by EPMA-EDX or WDX, RBS, SNMS and AES. It was found that in some cases the results of composition analysis can significantly deviate from each other. At least two main reasons for these deviations exist: the different lateral resolution and the application of different reference samples for the calibration. Received: 3 June 1996 / Revised: 14 October 1996 / Accepted: 16 October 1996     

Reactions between YBa2Cu3O7−δ and La2O3 and SrCO3

Solid state reactions at 925°C between the high-T _c ceramic superconductor YBa₂Cu₃O_7?δ and La₂O₃ and SrCO₃, respectively, mixed in various molar ratiosr=MeO_n/YBa₂Cu₃O_7?δ, were studied using X-ray powder diffraction and scanning electron microscopy. The reaction between YBa₂Cu₃O_7?δ and La₂O₃ yielded (La_1?xBa_x)₂CuO_4?δ, withx≈0.075?0.10. La_2?xBa_1+xCu₂O_6?δ, withx≈0.2?0.25 and La-doped (Y_1?xLa_x)₂BaCuO₅, withx≈0.10?0.15. Forr=3.0, Y-doped La₂BaCuO₅ resulted also. The reaction between YBa₂Cu₃O_7?δ and SrCO₃ yielded (Sr_1?zBa_z)₂CuO₃, withz≈0.1, Y₂(Ba_1?zSr_z)CuO₅, withz=0.1?0.15, and a nonsuperconducting compound with an approximate composition of Y(Ba_0.5Sr_0.5)₅Cu_3.5O_10±δ. At values ofr≤2.0, unsubstituted YBa₂Cu₃O_7?delta was found in the reaction products.     

电流注入对La0.8Te0.2MnO3/YBa2Cu3O7-δ双层结构中YBa2Cu3O7-δ超导电性的影响

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.     

Chemical interactions in the systems BaCuO2-PbO and YBa2Cu3O7-PbO

Chemical interactions were found to occur in the systems BaCuO₂-PbO and YBa₂Cu₃O₇-PbO at 600–800C. The chemical peculiarities of these reactions are explained on the basis of redox transformations, with formation of the phase BaPbO₃.

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Zusammenfassung Bei 600–800C konnte im System BaCuO₂-PbO und YBa₂Cu₃O₇-PbO eine chemische Wechselwirkung festgestellt werden. Die chemische Besonderheit der Reaktionen wurde mit Hilfe von Redoxumformungen unter Bildung der Phase BaPbO₃ erklÄrt.

     

Kinetics of Structure Formation of YBa2Cu3O7-y

The kinetics of the synthesis of YBa₂Cu₃O_7-y (YBCO) was studied in situ on an X-ray diffractometer using the time vs temperature dependences of the concentration of the phase. The highest rate of YBCO synthesis was observed at 750-780°C. The effective activation energy was minimal at 700°C, E _a = 20-30 kJ/mole. The structural nonhomogeneity parameters and the dimensions of coherent scattering regions were determined for the YBCO product.     

YBa2CU3O7-δ掺杂PbO和BaPbO3的性质研究

测量了不同含量PbO和BaPbO3掺杂YBa2Cu3O7-δ的熔化温度和超导临界转变温度(T.).在YBa2Cu3O7-δ中掺入PdO可以降低熔点,但X射线衍射分析表明高温下YBa2Cu3O7-δ与PdO发生了反应生成BaPbO3,降低了样品的超导电性.分别用BaCO3与PdO,BaCO3与PdO2合成了单相的BaPdO3.在YBa2Cu3O7～δ中添加了不同含量的BaPdO3(10%,20%,30%).X射线衍射分析表明YBa2Cu3O7-δ与BaPbO3没有发生反应.掺杂了BaPbO3的YBa2Cu3O7-δ比掺杂PdO具有较好的超导电性,但是不能降低YBa2Cu3O7-δ的熔点.     

Thermal investigations of reactive powder mixtures as precursors for melt-processing of YBa2Cu3O7−x

DTA and XRD measurements were carried out with reactive precursors taken from the YO_1.5-BaO-CuO system in order to investigate mechanisms of YBa₂Cu₃O_7–x formation. The reactions taking place depend strongly on phase composition, phase purity, powder size and heating rate. Among the examined reactive precursors a mixture of 7Y₂O₃+22BaCuO₂+10CuO turned out as the most suited for melt-processing.     

Phase diagrams for the YBa2Cu3O7 family — ANNO 1996

Phase diagrams for cuprates of alkaline earth and rare earth elements are presented, covering binary to quintenary oxides and including selected solid solution series with other elements. Elementary crystal chemical data are included for identification of the occurring phases. Chemical stability is discussed with respect to the high-temperature reactions with Lewis acids like CO₂, protons, etc. Particularly the occurrence of oxide carbonates is consistently pointed out as one of the possible reasons for contradictory results in phase diagrams which comprise oxides with high basicity.     

X-ray photoelectron study of the state of Ba atoms in YBa2Cu3O7−δ doped with Co and Zn atoms

Investigating changes in the charged state of atoms upon superconductivity-suppressing substitutions is one of the methods to examine a relationship between the electronic structure of HTSC materials and the transition temperature to the superconducting state. In this paper, we measured E_bnd of the inner levels of Ba atoms in Co- and Zn-doped YBa₂Cu₃O_7−δ by X-ray photoelectron spectroscopy. Upon copper substitution by Co and Zn atoms, E_bnd of the inner levels diminishes for Ba atoms but remains the same for Cu and O atoms. The change of E_bnd of the inner levels of Ba atoms is attributed to the change of the Fermi level position in the “anionic” sublattice of (Cu₃O_7−δ)⁷⁻. Institute of Inorganic Chemistry, Siberian Branch, Russian Academy of Sciences. Translated fromZhurnal Strukturnoi Khimii, Vol. 35, No. 4, pp. 91–95, July–August, 1994. Translated by L. Smolina