Investigations of Bi substitution in NdBa2Cu3Oy
01 Aug 1991-Journal of Superconductivity (Kluwer Academic Publishers-Plenum Publishers)-Vol. 4, Iss: 4, pp 289-296
TL;DR: In this paper, the authors explored the possibility of substituting Bi for Nd in orthorhombic NdBa2Cu3O676, a new cubic compound witha=0.8703 nm, and showed that a poorly crystallized oxygen-deficient form of this compound is already present prior to reheating.
Abstract: Attempts to substitute Bi for Nd in orthorhombic NdBa2Cu3O
y
, prepared in air or oxygen at about 950°C led instead to formation of Ba2NdBiO6, a new cubic compound witha=0.8703 nm. The possibility was then explored of preparing superconducting (Nd1−x
Bi
x
)Ba2Cu3O
y
, by first forming the tetragonal phase at 880–950°C in nitrogen or argon followed by reheating in oxygen or air at 250–500°C in order to insert the additional oxygen required to yield the orthorhombic form while avoiding oxidation of Bi3+ to Bi5+. X-ray diffraction studies, electrical conductivity measurements, and thermogravimetric analysis of products indicate that Bi does not enter the NdBa2Cu3O
y
, lattice in either the tetragonal or the orthorhombic phase. Ba2NdBiO6 clearly forms on reheating in oxygen or air even at low temperatures, and evidence is presented that a poorly crystallized oxygen-deficient form of this compound is already present prior to the reheating.
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TL;DR: In this article, the influence of the amount of liquid phase on the X-ray diffraction data and electrical properties is reported, and the effect of different liquid phases on the electrical resistance versus temperature measurements is discussed.
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TL;DR: The effective ionic radii of Shannon & Prewitt [Acta Cryst. (1969), B25, 925-945] are revised to include more unusual oxidation states and coordinations as mentioned in this paper.
Abstract: The effective ionic radii of Shannon & Prewitt [Acta Cryst. (1969), B25, 925-945] are revised to include more unusual oxidation states and coordinations. Revisions are based on new structural data, empirical bond strength-bond length relationships, and plots of (1) radii vs volume, (2) radii vs coordination number, and (3) radii vs oxidation state. Factors which affect radii additivity are polyhedral distortion, partial occupancy of cation sites, covalence, and metallic character. Mean Nb5+-O and Mo6+-O octahedral distances are linearly dependent on distortion. A decrease in cation occupancy increases mean Li+-O, Na+-O, and Ag+-O distances in a predictable manner. Covalence strongly shortens Fe2+-X, Co2+-X, Ni2+-X, Mn2+-X, Cu+-X, Ag+-X, and M-H- bonds as the electronegativity of X or M decreases. Smaller effects are seen for Zn2+-X, Cd2+-X, In2+-X, pb2+-X, and TI+-X. Bonds with delocalized electrons and therefore metallic character, e.g. Sm-S, V-S, and Re-O, are significantly shorter than similar bonds with localized electrons.
51,997 citations
IBM1
TL;DR: In this paper, Ba−La−Cu−O system, with the composition BaxLa5−xCu5O5(3−y) have been prepared in polycrystalline form, and samples with x=1 and 0.75,y>0, annealed below 900°C under reducing conditions, consist of three phases, one of them a perovskite-like mixed-valent copper compound.
Abstract: Metallic, oxygen-deficient compounds in the Ba−La−Cu−O system, with the composition BaxLa5−xCu5O5(3−y) have been prepared in polycrystalline form. Samples withx=1 and 0.75,y>0, annealed below 900°C under reducing conditions, consist of three phases, one of them a perovskite-like mixed-valent copper compound. Upon cooling, the samples show a linear decrease in resistivity, then an approximately logarithmic increase, interpreted as a beginning of localization. Finally an abrupt decrease by up to three orders of magnitude occurs, reminiscent of the onset of percolative superconductivity. The highest onset temperature is observed in the 30 K range. It is markedly reduced by high current densities. Thus, it results partially from the percolative nature, bute possibly also from 2D superconducting fluctuations of double perovskite layers of one of the phases present.
10,272 citations
TL;DR: A stable and reproducible superconductivity transition between 80 and 93 K has been unambiguously observed both resistively and magnetically in a new Y-Ba-Cu-O compound system at ambient pressure.
Abstract: A stable and reproducible superconductivity transition between 80 and 93 K has been unambiguously observed both resistively and magnetically in a new Y-Ba-Cu-O compound system at ambient pressure. An estimated upper critical field H c2(0) between 80 and 180 T was obtained.
5,965 citations
TL;DR: In this paper, a new high-Tc oxide superconductor of the BiSrCa-Cu-O system without any rare earth element was discovered, which has Tc of about 105 K, higher than that of YBa2Cu3O7 by more than 10 K.
Abstract: We have discovered a new high-Tc oxide superconductor of the Bi-Sr-Ca-Cu-O system without any rare earth element. The oxide BiSrCaCu2Ox has Tc of about 105 K, higher than that of YBa2Cu3O7 by more than 10 K. In this oxide, the coexistence of Sr and Ca is necessary to obtain high Tc.
2,698 citations
TL;DR: The single-phase perovskite Ba0.6K0.4BiO3 has a magnetically determined onset temperature of 29.8 K, a Tc considerably higher than that of conventional superconductors and surpassed only by copper-containing compounds.
Abstract: It is well known that the breakthrough of Bednorz and Muller1 in discovering superconductivity in (La, Ba)2CuO4 was inspired in part by their knowledge of the superconducting properties of Ba(Pb, Bi)O3 (ref. 2). With a transition temperature, Tc, of ∼12 K, that compound was not generally considered anomalous despite the fact that its Tcis 3–5 times higher than that of traditional superconductors with comparable density of states3–5. The increases in Tc for copper-oxide-based materials continue to generate worldwide excitement, but from both a chemical and theoretical point of view it would also be exciting if high-Tcsuperconductivity were observed in another class of materials. Here we report the results of experiments leading us to the single-phase perovskite Ba0.6K0.4BiO3, which has a magnetically determined onset temperature of 29.8 K—a Tc considerably higher than that of conventional superconductors and surpassed only by copper-containing compounds. Superconductivity in this compound occurs within the framework of a three dimensionally connected bismuth-oxygen array. These results suggest that further research toward exploring the limiting Tcs for bismuth-oxide-based, high-temperature superconductors might be fruitful.
972 citations