R.J. Cava

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

Fabrication and properties of epitaxial ferroelectric heterostructures with (SrRuO3) isotropic metallic oxide electrodes

Epitaxial ferroelectric SrRuO3/Pb(Zr0.52Ti0.48)O3/SrRuO3 heterostructures have been fabricated employing isotropic metallic oxide electrodes on (100) SrTiO3 and (100) Si with an yttria stabilized zirconia buffer layer. The structures have been grown in situ by 90° off‐axis sputtering, which allows the growth of uniform stoichiometric films over large areas with excellent step coverage. X‐ray diffraction, Rutherford backscattering spectroscopy, and cross‐sectional transmission electron microscopy reveal high crystalline quality and coherent interfaces. They exhibit superior fatigue characteristics over those made with metal electrodes, showing little degradation over 1010 cycles, with a large remnant polarization.

The crystal structures of the lithium-inserted metal oxides Li0.5TiO2 anatase, LiTi2O4 spinel, and Li2Ti2O4

The crystal structures of three lithium titanates by neutron diffraction powder profile analysis were determined. The tetragonal anatase form of TiO2 becomes orthorhombic on ambient-temperature lithium insertion to Li0.5TiO2 due to the formation of TiTi bonds. The lithium partially occupies the highly distorted octahedral interstices in the anatase framework in fivefold-coordination with oxygen. Cubic LiTi2O4 formed by heating Li0.5TiO2 anatase has a normal spinel structure with Li in the tetrahedral sites. In Li2Ti2O4 formed by reacting LiTi2O4 spinel with n-BuLi at ambient temperature, the titanium remains in the spinel positions but the lithium is displaced, filling all the available octahedral sites.

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.

Structural anomalies at the disappearance of superconductivity in Ba2YCu3O7−δ: Evidence for charge transfer from chains to planes

Abstract In systematic studies of oxygen-deficient Ba 2 YCu 3 O 7−δ , we have found that a structural anomaly occurs at the composition where bulk superconductivity disappears. The observed step-like increase in the c lattice parameter, when associated with changes in the atomic positions within the unit cell, indicates that superconductivity is lost due to a charge redistribution from the copper-oxygen chains to the copper-oxygen planes. This is microscopic experimental evidence establishing the role of secondary structural elements in the layered copper-oxide high- T c superconductors.

Ternary LixTiO2 phases from insertion reactions

Lithium insertion reactions in the various close packed TiO2 frameworks is discussed. Preliminary neutron diffraction powder profile analysis data is presented for the lithium inserted anatase Li0.5TiO2, the spinel LiTi2O4, and the lithiated spinel Li2Ti2O4. A simple model based on minimizing cation repulsion is used to rationalize the structures and diffusion of lithium.

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.