J. D. Jorgensen’s research while affiliated with Lawrence Livermore National Laboratory and other places

The 2nd Polish-US Conference held at Wrocław and Karpacz, Poland, 17-21 August 1998; Proceedings: New Developments in High Temperature Superconductivity, Springer LNP 545, Eds. J. Klamut, B.W. Veal, B.M. Dabrowski, P.W. Klamut, M. Kazimierski

The crystal structure of PrCoO 3 has been studied with high-resolution neutron powder diffraction and pair-distribution-function analysis in the temperature range from 12–600 K. The compound has the orthorhombic (Pbnm) perovskite structure over the entire temperature range. The temperature dependence of the average Co-O bond length shows clear anomalies near 60 K and 200 K where anomalous temperature dependencies of thermal conductivity and magnetic susceptibility have been reported. The data show a constant intermediate-spin-state fraction within 60 < T < 200 K and excitation of high-spin-state Co(III) above 200 K.

Mixed-conducting ceramic oxides have potential uses in high-temperature electrochemical applications such as solid oxide fuel cells, batteries, sensors, and oxygen-permeable membranes. The Sr-Fe-Co-O system combines high electronic/ionic conductivity with appreciable oxygen permeability at elevated temperatures. Dense ceramic membranes made of this material can be used to separate high-purity oxygen from air without the need for external electrical circuitry, or to partially oxidize methane to produce syngas. Samples of SrâFe{sub 3-x}CoâO{sub y} (with x = 0, 0.6, 1.0, and 1.4) were prepared by solid-state reaction method in atmospheres with various oxygen partial pressures (pOâ) and were characterized by X-ray diffraction, scanning electron microscopy, and electrical conductivity testing. Phase components of the sample are dependent on cobalt concentration and pOâ. Electrical conductivity increases with increasing temperature and cobalt content in the material.

The mixed-conducting Sr-Fe-Co oxide has potential use as a gas separation membrane. Its superior oxygen transport reveals the feasibility of using oxide membranes in large-scale oxygen separation. Sr2Fe3-xCoxOy (with x = 0.0, 0.3, 0.6, and 1.0) samples were made by solid state reaction. To understand the oxygen transport mechanism in this system, conductivity and thermogravimetry experiments were conducted at high temperature in various oxygen partial pressure environments. The oxygen diffusion coefficient was determined from the time relaxation transient behavior of the specimen after switching the surrounding atmosphere. Mobility of the charge carrier was derived from relative conductivity and weight changes. X-ray diffraction experiments were carried out on these samples to determine their crystal structures.

The potential applications of mixed-conducting ceramic oxides include solid-oxide fuel cells, rechargeable batteries, gas sensors and oxygen-permeable membranes. Several perovskite-derived mixed Sr-Fe-Co oxides show not only high electrical-conductivity but also appreciable oxygen-permeability at elevated temperatures. For example, dense ceramic membranes of SrFeCo0.5O3-δ can be used to separate oxygen from air without the need for external electrical circuitry. The separated oxygen can be directly used for the partial oxidation of methane to produce syngas. Quantitative phase analysis of the SrFeCo0.5O3-δ material has revealed that it is predominantly composed of two Sr-Fe-Co-O systems, Sr4Fe6-xCoxO13 and SrFe1−xCoxO3-δ. Here we report preliminary structural findings on the SrFe1−xCoxO3-δ (0 ≤ x ≥ 0.3) system.

We discuss the effects of doping on the Cu chain sites in YBa2Cu3−xMxO6+y. The relationship between bond lengths obtained from neutron scattering and charge transfer is evaluated in terms of bond valence. In particular, it is concluded that removing an oxygen from the chains transfers one electron to the planes. How to Cite This Article Link to This Abstract Blog This Article Copy and paste this link Highlight all http://dx.doi.org/10.1557/PROC-156-119 Citation is provided in standard text and BibTeX formats below. Highlight all BibTeX Format @inproceedings{OPL:8118834,author = {Miceli,P. F. and Tarascon,J. M. and Greene,L. H. and Barboux,P. and Jorgensen,J. D. and Rhyne,J. J. and Neumann,D. A.},title = {Charge Transfer and Bond Lengths in YBa2Cu3−xMxO6+y},booktitle = {Symposium M – High Temperature Superconductors: Relationships Between Properties, Structure, and Solid State Chemistry},series = {MRS Proceedings},volume = {156},year = {1989},doi = {10.1557/PROC-156-119},URL = {http://journals.cambridge.org/article_S1946427400386043},} Click here for full citation export options. Blog This Article Blog This Article : Highlight all Charge Transfer and Bond Lengths in YBa2Cu3−xMxO6+y P. F. Miceli,J. M. Tarascon,L. H. Greene,P. Barboux,J. D. Jorgensen,J. J. Rhyne and D. A. Neumann (1989). MRS Proceedings , Volume 156 , 1989, 119 http://journals.cambridge.org/action/displayAbstract?aid=8118834 The code will display like this Charge Transfer and Bond Lengths in YBa2Cu3−xMxO6+y P. F. Miceli, J. M. Tarascon, L. H. Greene, P. Barboux, J. D. Jorgensen, J. J. Rhyne and D. A. Neumann 1989 MRS Proceedings, ,Volume156, 1989, 119 http://journals.cambridge.org/abstract_S1946427400386043 P. F. Miceli, J. M. Tarascon, L. H. Greene, P. Barboux, J. D. Jorgensen, J. J. Rhyne and D. A. Neumann (1989). Charge Transfer and Bond Lengths in YBa2Cu3−xMxO6+y. MRS Proceedings, 156, 119 doi:10.1557/PROC-156-119. 0Comments

We have determined the crystal structures of five phases in the Bal-xKxBiO3 system for 0≤x≤0.5 and 10K≤T≤473K. Superconductivity occurs only in a cubic perovskite phase with the maximum Tc at the transition to an orthorhombic, Ibmm, phase. The commensurate structure of this orthorhombic phase, which involves only tilting of the Bi06 octahedra, provides no explanation for its non-metallic behavior. However, an incommensurate structural modulation, observed by electron diffraction, may provide a rationalization. Thus, the maximum Tc at the phase boundary may result from competition between superconductivity and a charge density wave. Further studies of the phase diagram at high temperatures, where controlled oxygen atmospheres are required, reveal an unusual reentrant formation of a potassium-containing impurity phase which explains the need for synthesis techniques that involve initially reacting in a reducing atmosphere, followed by oxygenation at lower temperature.

Single‐phase samples of (Ba1‐xKx)(Bi1‐xSby)O3 have been synthesized over a limited compositional range using a two‐step procedure: high‐temperature firing in a low oxygen partial pressure followed by low‐temperature oxygen annealing. For y=0 and 0.37<x<0.50, samples have a simple cubic structure and are bulk superconductors with Tc gradually decreasing from 30 to 22K as x increases to 0.50. For fixed x and y>0 samples are superconducting again with a simple cubic structure and with Tc gradually decreasing as y increases.

Atomic pair distribution function analysis has demonstrated displacements of Tl and O atoms within the Tl-O layers with shortrange ordering of lower symmetry than the crystallographic lattice. Two models have been proposed for these displacements. Rietveld analysis neither confirms nor contradicts these models. Temperature-dependent PDF measurements show changes in local structure correlating with temperature.

The phonon densities-of-states (DOS) of superconducting Ba 1−x K x Bi ¹⁶ O 3 and Ba 1−x K x Bi ¹⁸ O 3 (x=0.4) are determined using molecular dynamics (MD) simulations and inelastic neutron scattering measurements. The reference isotope-effect exponent is obtained from the mass variation of the first frequency moment of the phonon DOS. The energy gap, oxygen isotope-effect exponent and electron tunneling characteristics are calculated within the framework of Eliashberg theory of electron-phonon coupling.