Cornelis A. H. A. Mutsaers

Properties of the tetragonal superconductor CaBaLaCu3Ox

Abstract The compound CaBaLaCu 3 O 6.9 is a tetragonal bulk superconductor with a T c of 80 K. CaBaLaCu 3 O x is isomorphic to tetragonal YBa 2 Cu 3 O x in which the Ca and La ions are both located at the Y- and Ba-site. High temperature X-ray diffraction and thermogravimetric measurements show no indication for “order-disorder” transitions involving the oxygen ions. TEM micrographs of CaBaLaCu 3 O x show no evidence for a / b twinning. The oxygen content and the partial oxygen pressure of CaBaLaCu 3 O x are determined as a function of temperature. The standard enthalpy change for the oxidation reaction, Δ H , is determined as 190.4(0.3) kJ⧸mol O 2 . Transmission electron diffraction patterns show weak but distinct half-order spots indicating an ordering which can be described by a supercell having axes twice as large as the basic unit cell.

Compounds and phase compatibilities in the system La2O3SrOCuO at 950°C

Abstract The subsolidus phase diagram of the system La 2 O 3 SrOCuO at 950°C under 1 bar of pure oxygen has been investigated and a new ternary compound, La 1+ x Sr 2− x Cu 2 O 5.5+δ with 0.05 ≤ x ≤ 0.15, was isolated. This compound crystallizes in an orthorhombic unit cell with lattice constants related to the lattice constant of the perovskite cubic unit cell, a p , by a = 3.80 A ≅ a p , b = 11.48 A ≅ 3 a p , and c = 20.23 A ≅ 5 a p . The structure is isotypical to that of Ln Sr 2 Cu 2 O 5.5+ δ with Ln = Sm, Eu, or Gd. Reported data on the crystal chemistry of the equilibrium compounds in the system La 2 O 3 SrOCuO have been summarized and compared with the present data. The structure of all compounds is built up of a LaO rock-salt layer separated by a number of LaCuO 3 perovskite layers. The general formula is (LaO)(LaCuO 3 ) n where La can be replaced either partly or completely by Sr. Compounds are found for n = 1, 2, and ∞. The structures of the compounds show different types of oxygen vacancy ordering.

Oxygen content, microstructure, and superconductivity of YBa2Cu3O7− x

The influence of preparation conditions and microstructure on the superconductive properties of single-phase poly-crystalline YBa 2 Cu 3 O 7− x was investigated by electron probe microanalysis, transmission electron microscopy (TEM), and x-ray powder diffraction as a function of temperature in various ambients supplemented by resistivity and susceptibility measurements. Leaching of Ba was observed when samples were brought in contact with water. The TEM imaging revealed that individual grains have an extremely defect-rich outer shell and an inner core with a domain structure with a and b axes interchanged. The transition temperature T c was found to decrease with increasing quench temperature in the range 400–900°C. The T c was observed to be linearly proportional to the difference in the orthorhombic cell parameters ( b-a ). Further implications are discussed.

Crystal structure and electrical conductivity of YBa4Cu3O8.5 + δ (δ = 0.0−0.5)

The crystal structure of YBa4Cu3O8.5 + δ(δ = 0.0−0.5) has been determined by electron diffraction and neutron powder diffraction measurements. The unit cell is cubic, space group Pm3 (200), Z = 2, with a = 2ap, where ap is the cubic perovskite lattice constant. The Cu ions are basically coordinated in squares, which are tilted 90° with respect to adjacent squares, and connected to form chains. The chains stretch along all three crystallographic axes and are interconnected by octahedrally coordinated Y ions. Between 77 K and 300 K the electrical conductivity of samples of YBa4Cu3O8.5 + δ is well described by the Mott law of variable-range hopping: σ = σ0 exp − (T0/T)14, which suggests that the electrical conductivity is due to thermally activated hopping between localized states. The values obtained for T0 of 3−5 × 107 K and for σ0of 5−7 × 107 Ω-1cm-1 are independent of the oxygen content.

Crystal structure and superconducting properties of Nd1+xBa2−xCu3O7+y

We present results of neutron-diffraction, AC-susceptibility and resistivity measurements on Nd 1+x Ba 2−x Cu 3 O 7+y (x = 0.0–0.5). It is found that the orthorhombic-to-tetragonal phase transition, which occurs between x=0.1 and 0.3, does not alter the superconducting properties drastically.

Structure and Composition in the Superconductive Bi-Sr-Ca-Cu-O System

Characterization of superconducting Bi--Sr--Ca--Cu oxides has been carried out by electrical measurements, x-ray diffraction, conventional and high-resolution electron microscopy, and electron microprobe analysis. Nominal starting compositions with cation ratios of 1:1:1:2 and 2:2:1:2 show considerably different superconducting behavior. In both cases multiphase materials are formed. The predominant superconducting phase occurs as thin platelets with an orthorhombic, modulated structure. These particles often have edges aligned along (110), (100), and (010) directions and contain subgrain boundaries. Electron diffraction patterns and high-resolution micrographs taken along several zone axes are consistent with an incommensurate centered modulation along the b axis with a magnitude of 4.7 +- 0.1 times b. Unexpectedly, two distinct chemical compositions were found in platelets with the same apparent structure: Bi/sub 4/Sr/sub 3/Ca/sub 3/Cu/sub 4/O/sub 16//sub +- //sub delta/ for the lower T/sub c/ phase in the 1:1:1:2 material, and Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub 8//sub +- //sub delta/ for the isomorphic higher T/sub c/ phase present in the 2:2:1:2 samples.

Point contacts from BiCaSrCu2Ox

The properties of point-contacts between two pieces of BiCaSrCu2Ox-material were investigated. At 4.2 K critical currents of 200 μA could be obtained. The IcR product was typically 5–10 mV. The derivatives of the I–V characteristics showed local maxima around 25 mV, indicating the possibility of an energy gap of about 13 mV. The shape of the I–V characteristics was to a large extend independent of the contact pressure.

Chemical mechanical polishing of aluminum for the 0.18 /spl mu/m dual damascene process

Chemical mechanical polishing of aluminum is used for the 0.18 /spl mu/m aluminum dual damascene process. Issues concerning the choice of slurry are discussed. Initial results show a yield of 80% on 3.15 m long and 0.4 /spl mu/m wide damascene lines. Comb structures have no shorts. At the same time, no Al line dishing was observed. The end-point-detection system on the Applied Materials MIRRA CMP tool is discussed.