W.F. Peck

Structural anomalies, oxygen ordering and superconductivity in oxygen deficient Ba2YCu3Ox

Abstract We report the characterization of series of oxygen deficient Ba2YCu3Ox samples for 7 ≥ x ≥ 6 prepared by Zr gettered annealing at 440°C. Measurements include complete crystal structure analysis at 5 K by powder neutron diffraction, electron microscopy study of the oxygen ordering, and magnetic measurements of the superconducting transitions, with particular attention to the transition widths. The results show for the first time that the 90 K and 60 K plateaus in Tc as a function of oxygen stoichiometry are associated with plateaus in the effective valence of the plane coppers. We also correlate the disappearance of superconductivity for x

Superconductivity near 70 K in a new family of layered copper oxides

A new family of high-temperature superconductors is described, with the general formula Pb2Sr2ACu3O8+δ. Although they have the planes of CuO5 square pyramids characteristic of the other copper-oxide superconductors, the new compounds belong to a distinct structural series, with wide scope for elemental substitution. Their unusual electronic configuration also gives new insight into the role of charge distribution among the structural building blocks in controlling superconductivity.

Zinc-indium-oxide: A high conductivity transparent conducting oxide

We report the fabrication and characterization of zinc‐indium‐oxide films with similar electrical conductivity and better transparency in both the visible and infrared compared with indium–tin–oxide, a widely used transparent conductor in many technological applications. Dramatically superior transmission properties in the 1–1.5 μm range in particular make zinc–indium–oxide attractive for use in infrared devices, where transparent electrodes are required. Resisitivities as low as 400 μΩ cm result from doping with small quantities of Sn; Al, Ga, and Ge are also effective dopants. Deposition on glass and quartz substrates as amorphous films by pulsed laser deposition and dc reactive sputtering is described.

Studies of oxygen-deficient Ba2YCu3O7−δ and superconductivity Bi(Pb)SrCaCuO

Abstract Ambient temperature measurements of the crystallographic cell parameters for oxygen deficient Ba 2 YCu 3 O 7−δ prepared by gettered annealing indicate the presence of microscopic differences in the oxygen configuration at fixed δ dependent on annealing temperature. The loss of superconductivity with increasing oxygen deficiency is shown to be due to a step-like increase in length of the plane copper-apical oxygen bond, and not to the orthorhombic to tetragonal transition. The crystal structure of the 84K superconductor Bi 2 Sr 2 CaCu 2 O 8+δ is described, as is the stabilization of 110K superconductivity via partial Pb/Bi substitution with long time annealing.

Structure and magnetic properties of epitaxial spinel ferrite thin films

We have grown epitaxial spinel ferrite thin films of (Mn,Zn) Fe2O4 and CoFe2O4 on (100) and (110) SrTiO3 and MgAl2O4 buffered by spinel structure buffer layers. High quality spinel ferrite films were grown at 400 °C on buffer layers that were grown at 600 °C and postannealed at 1000 °C. Although (Mn,Zn) Fe2O4 grown directly on SrTiO3 and MgAl2O4 shows mediocre structural and magnetic properties, ferrite films grown on (100) and (110) SrTiO3 and MgAl2O4 buffered with CoCr2O4 exhibit excellent crystallinity and bulk saturation magnetization values, thus indicating the importance of lattice match and structural similarity between the film and the immediately underlying layer.

Transparent conducting thin films of GaInO3

GaInO3 is recently identified transparent conducting material which is structurally and chemically distinct from indium tin oxide [R. J. Cava, J. M. Phillips, J. Kwo, G. A. Thomas, R. B. van Dover, S. A. Carter, J. J. Krajewski, W. F. Peck, Jr., J. H. Marshall, and D. H. Rapkine, Appl. Phys. Lett. 64, 2071 (1994)]. We have used both dc reactive sputtering in the on‐ and off‐axis geometries and pulsed laser deposition to grow films of this material. Layers of pure GaInO3 as well as those partially substituted with Ge for Ga or Sn for In have been studied. Both growth techniques are capable of producing films with conductivity ∼400 (Ω cm)−1 and transmission as high as 90% throughout the visible spectrum for ∼1‐μm‐thick films. The growth techniques differ in the morphology of the films produced as well as in the degree of dopant incorporation that can be achieved. A post‐growth anneal in H2 can help produce an optimized oxygen content and a reduction of resistivity. Hall measurements indicate a carrier conce...

Neutron powder diffraction study of Pb2Sr2YCu3O8, the prototype of a new family of superconductors

Abstract The structure of Pb 2 Sr 2 YCu 3 O 8 has been analyzed with powder neutron diffraction techniques and profile analysis. The results of this study confirm the general structural features determined by X-ray single-crystal methods. The material has pseudo tetragonal symmetry, but is orthorhombic, space group Cmmm with lattice parameters a =5.3933(2), b =5.4311(2), and c =15.7334(6)A. The orthorhombic distortion is caused by the disordering in the ab plane of the oxygen atoms of the PbO layers over the general position of the space group, with x =0.275(5) and y =0.402(5) A. The structure of this compound can be derived from that of YBa 2 Cu 3 O 6 by substituting the Cu layers with blocks of … PbO.Cu.PbO… . Of the two Cu atoms in the asymmetric unit, one has two fold coordination while the other has five fold pyramidal coordination with the apex elongated along the c -axis.

GaInO3: A new transparent conducting oxide

GaInO3, a layered material with the β Ga2O3 crystal structure, can be doped with electrons through the introduction of oxygen deficiency, Sn doping for In, or Ge doping for Ga. At atomic doping levels of 10% or less, resistivities as low as 3 mΩ cm are obtained. In contrast to polycrystalline indium tin oxide (ITO), which is distinctly green, conductive gallium indium oxide is light grey with no visible coloration. Thin films of doped GaInO3 display good transparency over the whole optical window, superior to that of ITO in the green‐blue region.

Crystal chemistry of the series LnT2B2C (Ln=rare earth, T=transition element)

Abstract The new LuNi 2 B 2 C-type structure has been investigated for different lanthanide atoms and transition metal elements. Single-crystal structure determinations were carried out for some representative compounds, and a linear regression fit was used to infer the positional parameter of the boron atom for the whole rare earth series. In this way, detailed bonding information for all phases in the series was obtained. A geometric model, based on the conservation of bond lengths, explains the behaviour of the lattice parameters for the different size lanthanides.

Superconductivity at 28 K in a cuprate with a niobium oxide intermediary layer

Abstract A new copper oxide based superconductor is reported based on the ordered interleaving of NbO 6 or TaO 6 octahedra between the apices of copper oxide pyramids. Good bulk superconductivity is observed for only a narrow range of temperatures, annealing times and cooling rates. The relatively low T c of the prototype compound Sr 2 Nd 1.5 Ce 0.5 NbCu 2 O 10−δ , may be due to the presence of the insulating NbO 6 layers or the wide (Nd, Ce) 2 O 2 layers which separate the CuO 2 planes.