Showing papers on "Inorganic compound published in 1992"

Superconductivity at 110 K in the infinite-layer compound (Sr1-xCax)1-yCuO2

Abstract: THE 'infinite-layer' parent structure1 of the copper oxide superconductors (Fig 1) is the simplest structure containing the CuO2 sheets that are apparently essential to high-transition-temperature (high-Tc) superconductivity At ambient pressure only Ca1-x SrxCuO2 with x≈Ol can be stabilized in this structure1,2but at high pressures and temperatures compounds ranging from Ba1/3Sr2/3CuO2 to Ca2/3Sr1/3CuO2 through SrCuO2 can be synthesized3 We have previously reported superconductivity with Tc = 40–100 K in the Ba–Sr–Cu–O system4,5 but have not until now been able to isolate a superconducting phase Here we report the isolation of an alkaline-earth-deficient infinite-layer phase, (Ca1-xSrx)1-yCuO2 (y~Ol), with Tc up to 110 K In contrast to Sr1-xRxCuO2 (with R a rare-earth element and Tc⩽43 K), which from the composition dependence of the lattice constants is thought to be an n-type superconductor6,7 our data suggest that the present superconductor is of p-type, with the carriers arising from calcium and strontium vacancies High-resolution electron micrographs reveal defect layers, which we suggest are where the calcium and strontium vacancies are concentrated

Lattice vibrations of CuInSe2 and CuGaSe2 by Raman microspectrometry

Abstract: The vibrational spectra of the chalcopyrite compounds CuInSe2 and CuGaSe2 have been studied by Raman microspectrometry. This technique is very useful in the present case where large single crystals are not generally available. The results have been used to resolve discrepancies in the reported data on the vibrational spectrum of CuInSe2.

Interatomic and Intra-Atomic Configuration Interactions in Core-Level X-Ray Photoemission Spectra of Late Transition-Metal Compounds

Abstract: We theoretically investigate X-ray photoemission spectra (XPS) from transition metal 2 p and 3 s core levels in late transition metal compounds in terms of an MX 6 cluster model (M=Mn∼Ni; X=halogen or oxygen), paying particular attention to the interplay between the intra-atomic multiplet coupling and covalency mixing effects. In the analysis of 3 s -XPS, we also take into account the intra-atomic configuration interaction between 3 s 1 3 p 6 3 d n and 3 s 2 3 p 4 3 d n +1 electron configurations. The systematic change of 2 p -XPS and 3 s -XPS on going from Ni to Mn compounds or from fluorides to bromides is mainly ascribed to that of the charge transfer energy from X to M ion. In the analysis, we show that the final state effects are very important in the 3 s -XPS as well as in the 2 p -XPS.

A new copper oxide superconductor containing carbon

Abstract: SUPERCONDUCTIVITY in the high-transition-temperature (high-Tc) copper oxide superconductors seems to arise from layers of copper–oxygen squares, pyramids or octahedra. Recently the compound Sr2CuO2CO3 was found to contain layers of CuO6 octahedra1 (Fig. 1), suggesting that it might be made superconducting by appropriate doping. But the presence of carbonate as an impurity is known to degrade the superconducting properties of materials such as and (refs 2, 3), much effort having been made to minimize residual carbon in these compounds by optimizing processing methods4. It is thus of some interest to see whether Sr2CuO2CO3 can be made superconducting despite the carbonate ions incorporated in the structure. Here we report the synthesis, at 50 atm oxygen partial pressure, of superconducting (0.4≤x≤0.65, y≈O.1), with Tc (onset) up to ∼40 K and zero resistance at up to ∼26K. The crystal structure contains CuO2 sheets alternating with , slabs, which serve as charge reservoir layers: substitution of ∼10% copper for carbon in the slabs introduces holes into the CuO2 sheets, making the compound superconducting.

Lattice Constants of Boron Carbides

Abstract: In this paper, the lattice constants of boron carbides are determined by powder X-ray diffraction for samples with compositions between about 7.7 and 20.5 at.% carbon. The boundaries of the single-phase region are at about 9 at.% carbon and near, but likely somewhat less than 20 at.% carbon. The composition dependence of the lattice constants thus established provides a method of assessing the carbon concentration of unknown materials. In particular, assignment of the approximate composition of single crystals used in previous studies allows for a systematic examination of changes in interatomic separation as a function of composition. These changes are discussed in terms of a structural model of the boron carbide solid solution.

.pi.-Bond strengths of H2X:YH2: X = Ge, Sn; Y = C, Si, Ge, Sn

Abstract: The molecular structures and π-bond strengths are determined using both MP2 and MCSCF+CI energies for a series of H 2 X=YH 2 compounds, where X=Ge or Sn and Y=C, Si, Ge, or Sn. These strengths are estimated both by evaluating the rotation barriers and by investigating the appropriate thermochemical cycles. The results show that C>Si∼Ge>Sn in their ability to form π-bonds

Transport and structural study of Tl2Ba2CuO6+ delta single crystals prepared by the KCl flux method.

Abstract: Tl 2 Ba 2 CuO 6+δ single crystals are prepared by a KCl flux method. Transport properties and crystal structures are investigated for the samples with various T c 's. The result of structural analysis indicates that the change of T c is caused by the overdoping of the hole carrier through excess oxygen located between double Tl-O sheets. The out-of-plane resistivity ρ c is larger than for YBa 2 Cu 3 O 7 , but smaller than for Bi 2 Sr 2 CaCu 2 O 8