Preparation and magnetic properties of high Tc (110 K) Bi-Sr-Ca-Cu-oxide superconductors

Herkert, W.; Neumueller, H.-W.; Wilhelm, Manfred

doi:10.1016/0038-1098(89)90388-8

Cited by 20 publications

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“…Majewski et al [6] showed that Bi excess is necessary to obtain nearly single-phase Bi(2223) ceramics. Combining both Bi and Cu excess, Herkert et al [33] obtained interesting results with a Bi 2.7 Sr 2 Ca 2 Cu 4 O y nominal composition, that was initially reported to approximately correspond to the composition of the Bi(2223) phase [34]. These results were later contested by Sastry and West [35][36][37][38] who claimed to have obtained single-phase samples with the stoichiometric Bi 2 Sr 2 Ca 2 Cu 3 O y composition by use of a mixture of Bi 2 CuO 4 and Sr 2−x Ca x CuO 3 phases as precursors.…”

Section: Introductionmentioning

confidence: 99%

Formation mechanism of the Pb free phase

Grivel

Flükiger

1998

Supercond. Sci. Technol.

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The reaction leading to the formation of the Pb free phase from calcined precursor powders has been studied by means of scanning electron microscopy, x-ray diffraction and differential thermal analysis. The observation of the transformations occurring at a fixed location on the surface of a pellet has shown that the formation of the phase crystallites occurs simultaneously with a gradual decomposition of the platelets initially present in the mixture. The present investigations are discussed in relation with the formation of the Pb substituted phase. It is shown that there is a close relationship between the formation mechanisms of the Pb free and the Pb substituted phases, which both can be described as a nucleation and growth process.

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Section: Introductionmentioning

confidence: 99%

Formation mechanism of the Pb free phase

Grivel

Flükiger

1998

Supercond. Sci. Technol.

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High‐T_c Superconductors

Bogner

Hoenig

1990

Advanced Materials

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Crystal structure, chemical composition, and extended defects of the high‐T_c (Bi,Pb)₂Sr₂Ca_n−1Cu_nO_4+2n+δ compounds

Eibl

1995

Microscopy Res & Technique

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This paper summarizes results obtained by high-resolution transmission electron microscopy on the crystal structure and microstructure of the (Bi,Pb)2Sr2Ca(n)-1CunO4 + 2n + delta high-Tc superconducting oxides. The experimental basis for the work presented here are high-resolution structure images obtained at ultra-thin (3 nm) areas of carefully prepared transmission electron microscope (TEM) samples. The analysis was carried out on a 400 kV TEM equipped with a pole piece yielding 0.17 nm point-to-point resolution. From the images obtained the projected crystal potential of the cations can be extracted directly, as confirmed by detailed image simulation. Structural analysis of the oxygen sublattice remains an unsolved problem by high-resolution TEM (HRTEM), mainly because of the small scattering factors, and thus the contribution of the oxygen sublattice to the image contrast is small. The (BiPb)2Sr2Ca(n)-1CunO4 + 2n + delta phases are modulated structures that can be understood as an average structure plus a superimposed displacement field. The crystal structure consists of BiO double layers and perovskite-type cuboids (containing Sr, Ca, Cu, and O), which are sandwiched between the BiO double layers. The displacement field can be directly analyzed by HRTEM, and the largest displacement amplitudes of 70 pm were determined for the Bi atoms in the n = 1 compound. The chemical composition of the n = 2 and n = 3 compounds was determined by EDX in the TEM for the cation sublattice. A significant (Ca + Sr) deficiency (approximately 10%) with respect to Cu was found. The (Sr + Ca)/Cu mole fraction ratio was 1.31 for the Bi-2212 phase and 1.14 for the Bi(Pb)-2223 phase. The oxygen content cannot be determined by EDX in the TEM with the accuracy necessary for a correlation with electrical and superconducting properties. The defect structure present in these materials, that is, intergrown lamellae with different crystal structures and equal or different chemical compositions, stacking faults, and grain boundaries, is summarized. The importance of grain boundaries for understanding and improving superconducting properties is emphasized.

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Preparation and magnetic properties of high Tc (110 K) Bi-Sr-Ca-Cu-oxide superconductors

Cited by 20 publications

References 3 publications

Formation mechanism of the Pb free phase

Formation mechanism of the Pb free phase

High‐T_c Superconductors

Crystal structure, chemical composition, and extended defects of the high‐T_c (Bi,Pb)₂Sr₂Ca_n−1Cu_nO_4+2n+δ compounds

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Preparation and magnetic properties of high Tc (110 K) Bi-Sr-Ca-Cu-oxide superconductors

Cited by 20 publications

References 3 publications

Formation mechanism of the Pb free phase

Formation mechanism of the Pb free phase

High‐Tc Superconductors

Crystal structure, chemical composition, and extended defects of the high‐Tc (Bi,Pb)2Sr2Can−1CunO4+2n+δ compounds

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Product

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High‐T_c Superconductors

Crystal structure, chemical composition, and extended defects of the high‐T_c (Bi,Pb)₂Sr₂Ca_n−1Cu_nO_4+2n+δ compounds