Showing papers on "Inorganic compound published in 1988"

Structure of (CuO) 2 double layers in superconducting YBa2Cu3O7

Abstract: Since the report that multiphase mixture with the nominal composition La2−xBaxCCuO4−J, exhibit possible superconductivity1, research on this class of quaternary oxides has increased enormously. The superconducting compound in the original mixture was rapidly identified as La1.85Ba0.15CuO42, and subsequent research concentrated on the most suitable cation substitutions in this compound. A new oxide with a considerably higher critical temperature, Tc, was very soon found in the phase system Y2O3-BaO–CuO3, later identified by several groups as YBa2Cu3O7–δ; and now commonly known as the 1–2–3 compound. Intensive activity in structural characterization followed including reports of various planar defects. Here we report an analysis, using high-resolution electron microscopy of planar defects in superconducting YBa2Cu3O7, revealing the identity of a CuO double layer intercalation. Within this double layer, the Cu atoms remain in planar fourfold coordination with O, identical to their arrangement in the single CuO layers of the YBa2Cu3O7 matrix.

Electronic Interaction between Metal Additives and Tin Dioxide in Tin Dioxide-Based Gas Sensors

Abstract: The electronic interaction of SnO2 with Ag and Pd particles dispersed on its surface was examined by means of X-ray photoelectron spectroscopy (XPS). The binding energies (BE) of Sn3d and O1s of Ag(1.5 wt%)-SnO2 and Pd(3.0 wt%)-SnO2, which were lower by 0.5–0.7 eV than those of pure SnO2 in the as-prepared state, shifted reversibly by reduction and oxidation treatments. These shifts in BE are shown to reflect the shifts of Fermi energy of SnO2 which are interacting electronically with the metal additives. The electronic interaction depended on the metal loading, being strongest at 1.5 wt% and 3.0 wt% loadings of Ag and Pb, respectively. The implication is that the electronic interaction is of primary importance to the inflammable gas detection by Ag-SnO2 sensors.

Controlled carbon doping of GaAs by metalorganic vapor phase epitaxy

Abstract: The controlled incorporation of carbon has been demonstrated for the metalorganic vapor phase epitaxy of GaAs. Carbon levels between 1016 and 1019 cm−3 can be achieved under typical growth conditions by using Ga(CH3)3 and either As(CH3)3 or mixtures of As(CH3)3 and AsH3. The carbon incorporation into GaAs goes through a minimum with growth temperature at ∼650 °C when using Ga(CH3)3 and As(CH3)3. The controlled addition of AsH3 monotonically decreases the carbon incorporation. The high carbon levels (≳1–2×1019 cm−3), greater than the reported solid solubility, are thermally stable with a low diffusion coefficient. The GaAs:C layers exhibit a low deep level concentration, ∼1013 cm−3, with only a single midgap trap present.

Stabilities and nature of the attractive interactions in HeBeO, NeBeO, and ArBeO and a comparison with analogs NGLiF, NGBN, and NGLiH (NG = He, Ar). A theoretical investigation

Abstract: Results of ab initio calculations are reported for HeBeO (l), NeBeO (2), ArBeO (3), HeLiF (4), ArLiF (9, HeBN (6), ArBN (7), and HeLiH (8). At the MP2/6-31G(d,p) level, the NGBeO structures 1-3 are predicted with rather short NG-Be distances, while for 4-8 significantly longer NG-X distances are found. Dissociation into the respective noble-gas atom NG and Be0 is calculated at the MP4(SDTQ)/6-311G(2df,2pd) level corrected by zero-point energies and basis set superposition error to be endothermic by 3.1 kcal/mol for 1, 2.2 kcal/mol for 2, and 7.0 kcal/mol for 3. For 4-8, dissociation energies Do I 0.1 kcal/mol are predicted. Interactions of NG with Be0 in 1-3 are investigated by analysis of the one-electron density distribution and compared with interactions between NG and Be in diatomic cations HeBen+, NeBen+, and ArBe\"+ ( n = 1, 2). It is concluded that the stability of NGBeO can be explained on the basis of relatively strong charge-induced dipole interactions typical of van der Waals complexes. Vibrational frequencies and infrared intensities are reported for 1-3 to aid experimental identification. For HeBeO and HeBN CASSCF geometry optimizations have additionally been performed using the 6-3 lG(d,p) basis set and a full-valence active space.

On the 110 K superconductor in the Bi-Ca-Sr-Cu-O system

Abstract: We found a new compound in the Bi-Ca-Sr-Cu-O system which has a different structure from the 80 K superconductor Bi2(Ca, Sr)3Cu2Oy. The c-dimension of this compound is ~37 A and is ~6 A longer than that of Bi2(Ca, Sr)3Cu2Oy. Although we have not obtained a single-phased sample yet, the clear correlation between the diamagnetic susceptibility just below 110 K and the content of this compound included in the sample strongly suggests that the compound with c≈37 A is responsible for the superconductivity of Tc~110 K.

Crystal Structures of Organic Superconductor, (BEDT-TTF)2Cu(NCS)2, at 298 K and 104 K

Abstract: The crystal structures of an organic superconductor (BEDT-TTF)2Cu(NCS)2 (Tc=10.4 K) at 298 K and 104 K are determined by X-ray analysis. The packing pattern of donors is nearly analogous to κ-(BEDT-TTF)2I3. The counter anion, Cu(NCS)2−, has no positional disorder and constructs a peculiar sheet where a copper ion is coordinated with a sulfur and two nitrogen atoms to form a one-dimensional polymer with a permanent dipole moment.

Room‐temperature exciton transitions in partially intermixed GaAs/AlGaAs superlattices

Abstract: Substantial increases are observed in the energies of room‐temperature exciton transitions in GaAs/AlGaAs superlattices which have been partially intermixed via the impurity‐free vacancy diffusion process. Localized intermixing of the layered structure was accomplished by selective deposition of a SiO2 capping layer followed by rapid thermal annealing at temperatures between 850 and 950 °C for 15 s. In the samples studied, the above process allows continuously variable energy shifts of at least 61 meV while still maintaining clearly resolved excitonic behavior. Shifting and broadening of the exciton transitions are studied using room‐temperature photoluminescence and photocurrent spectroscopies. A transmission resonance calculation is used to determine the interdiffusion coefficient as a function of temperature from the measured energy shifts.

X-Ray Diffraction Study on the Crystal Structure of Nd1+xBa2-xCu3O7-δ

Abstract: Crystal structures in the Nd1+xBa2-xCu3O7-δ system have been investigated by X-ray powder diffraction combined with Rietveld analysis The compound NdBa2Cu3O7-δ is isomorphic with orthorhombic YBa2Cu3O7-δ With the increase of x the orthorhombic distortion decreases, and the compound becomes tetragonal at x=02 The tetragonal structure is isomorphic with the tetragonal form of YBa2Cu3O7-δ Tc of the compounds with x=0 and 005 is above 90 K, which decreases monotonically with x and the compound becomes semiconducting at x=04

Tl2Pt(CN)4: a non-columnar, luminescent form of Pt(CN)42- containing platinum-thallium bonds

Abstract: Tl 2 Pt(CN) 4 cristallise dans le systeme monoclinique, groupe d'espace P2 1 /n et sa structure est affinee jusqu'a R=0,063

Preparation and characterization of some AIBIICV type semiconductors

Abstract: Crystals of LiZnP, LiCdP, and LiZnAs are prepared by direct fusion of constituent elements. All three materials are found to be p‐type semiconductors. Absorption edge and photoconductivity spectra are measured. Band gaps are estimated to be 1.25 eV for LiZnAs, 1.3 eV for LiCdP, and 2.1 eV for LiZnP.