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.

Dense ceramic tubes of the multi phase mixed ionic/electronic conductor SrFeCo0.5Oy (SFC2) have been synthesized by solid-state reaction, Stability of the component phases of SFC2 was studied by insitu neutron diffraction in the temperature range of 900-1200 degreesC in air and Ar environments. In air between 900 and 1050 degreesC, the material is stable, with Sr-2(Fe,Co)(3)O-y (236) being the major phase. Above 1050 degreesC, 236 undergoes decomposition into perovskite and rocksalt phases, and at 1200 degreesC, only a small fraction of the 236 phase is stable. In Ar, the 236 phase is completely stable at 900 degreesC but is completely decomposed by 1100 degreesC, whereupon only the perovskite and rocksalt phases remain. Rietveld analysis indicates that the 236 and perovskite phases become more Fe-rich as decomposition occurs, while the perovskite phase lattice parameter and oxygen content vary readily as temperature and gas environment are changed. (C) 2002 Published by Elsevier Science Ltd.

Dense ceramic bars of the perovskite material SrFe0.8Co0.2O3−δ have been synthesized by solid-state reaction and studied by in-situ neutron diffraction through the range of oxygen partial pressure (pO2) from 10−0.68 to 10−13.3 atm at 900 °C. Over the complete range, the material retains the cubic perovskite structure and is stable even when δ>0.5. Between air and log pO2=−2.3, δ increases from 0.35 to 0.44 and the lattice expands. Lowering the pO2 further leads to an oxygen content "plateau" at δ≈0.5, through a log pO2 range of −3.5 to −8.6. Below this, the lattice undergoes further expansion, as oxygen is lost, most likely when Co3+ undergoes reduction to Co2+. Rietveld analysis indicates that there is no deviation from the Fe/Co 80:20 ratio over the entire pO2 range. The behavior of this perovskite is compared to that of the perovskite phase of similar composition found in a SrFeCo0.5Oy ceramic membrane material studied under similar conditions.

In-situ neutron and X-ray diffraction experiments were used to determine the crystal structure of Ba2In2O5 as related to temperature. Ba2In2O5 has a Brownmillerite-type crystal structure from room temperature to 900 °C, consisting of an orthorhombic unit cell with lattice parameters 6.0864(3)×16.7903(7)×5.9697(3) Å and Icmm (74) space group symmetry. At 900 °C, oxygen vacancies begin to disorder. By 925 °C, barium indate crystallizes in a tetragonal, 6.0348(4)×17.0688(22) Å, unit cell with I4cm (108) space group symmetry. This oxygen vacancy order–disorder transition is associated with an evolution to fast oxide-ion conduction. At 1040 °C, Ba2In2O5 becomes a cubic oxygen-deficient perovskite, 4.2743(1) Å, in the Pm3m space group. At 1080 °C, Ba2In2O5 begins to decompose.

Mixed-conducting Sr-Fe-Co oxides have potential applications in dense ceramic membranes for high-purity oxygen separation and/or methane conversion to produce syngas (CO + H-2), because of their combined high electronic/ionic conductivity and significant oxygen permeability. SrFeCoo(0.5)O(y) has been synthesized by the solid-state reaction method. Conductivities were measured at elevated temperatures in various gas environments and increased as temperature and oxygen partial pressure (p(O2)) increased in the surrounding environment. Neutron powder diffraction experiments revealed that in a high p(O2) environment the SrFeCo0.5Oy material consists of three different phases. The relative concentration of each component phase is dependent on temperature and p(O2) in the surrounding environment. In air, Sr-2(Fe,CO)(3)O-y (236-phase) is the majority phase and consists of > 75 wt% of the total, whereas the perovskite and rocksalt phases account for similar to20 and < 5 wt%, respectively. However, in a reducing environment, the 236-phase decomposes and converts to perovskite and rocksalt phase at high temperature. In an environment of p(O2) < 10(-12.2) atm, the 236-phase is completely converted into perovskite (brownmillerite) and rocksalt phases.

Solid solutions of LixNa1-xNiO2 Were synthesized and their structures were determined by Rietveld analysis using time-of-flight (TOF) neutron diffraction data. Three phases Were observed: monoclinic (C2/m) phase With x = 0.00, rhombohedral(l) (R m) phase with 0.13 < x < 0.15, rhombohedral(II) (R (3) over barm) phase with 0.70 < x < 1.00. Rietveld analysis of the rhombohedral(l) phase indicated no Ni disordering at the Li/Na (3a) site, and the disappearance of the cooperative Jahn-Teller ordering corresponds to the distance changes between the adjacent Ni layers, Magnetic properties were also measured for these phases. (C) 2002 Elsevier Science B.V. All rights reserved.

Samples have, been prepared with nominal composition Li-x(NiyCo1-y)O-2 (x approximate to 1.25, y = 0.7-1.0) with the structures being examined using Rietveld analysis of X-ray diffraction data. Rietveld analysis shows that the samples prepared with y = 0.70 and 0.75 have no Ni present on the 3a Li site, with all other samples showing a small degree of nonstoichiometry. Structural analysis of the 3b Ni + Co occupancy also suggests the possibility of 3b site disorder, which is in agreement with the results of previous studies.Charge/discharge measurements show an increase in discharge capacity with increasing Ni content, which suggests cobalt plays a very small part in the electrochemical capacities of these phases using the current voltage Limits. Samples with y = 0.75, 0.8 and 0.85 were found to have Very high efficiencies over a number of cycles, typically > 99% over 15 cycles. Samples prepared with y = 0.85 and 0.90 show evidence of a phase change which resembles that seen for LiNiO2. This would suggest that the stabilizing effects of Co in Li-x(NiyCo1-y)O-2 is lost when y greater than or equal to 0.85. Therefore, these particular compositions are probably not suitable for use in Li ion cells. (C) 2001 Elsevier Science B.V. All rights reserved.

The structure of the layered phase was studied extensively by powder X‐ray and neutron diffraction, and the relationships between the sintering temperature, structure, and electrochemical properties were determined. Samples in this study were prepared with a sintering time of 48 h at 600–750°C, and all indicated the presence of Ni on the Li site, based on structural analysis by the Rietveld method. The sample with the lowest level of Ni (~2.0%) on the Li site was prepared at 725°C. Structural analysis also indicated that the occupancy of the Ni/Co layer varied as a function of the sintering temperature, but as the sintering temperature was increased, the deviation from the expected value decreased. Electrochemical measurements were carried out on these samples, and the best sample in terms of electrochemical properties was that prepared at 725°C. This sample exhibited initial discharge capacities of ~190 mAh/g. All other samples delivered lower capacities, behavior which correlates with the degree of Li site disordering. These results clearly show the role of 3a site disorder on the electrochemical properties of these materials. However, we have not determined the role of the Ni/Co site, in particular, the disorder on electrochemical properties. © 2000 The Electrochemical Society. All rights reserved.

Mixed-conducting Sr-Fe-Co oxides have potential applications in dense ceramic membranes for high-purity oxygen separation and/or methane conversion to produce syngas (CO + H{sub 2}), because of their combined high electronic/ionic conductivity and significant oxygen permeability. SrFeCo{sub 0.5}O{sub y} has been synthesized by the solid-state reaction method. Conductivities were measured at elevated temperatures in various gas environments and rose with increasing temperature and increasing oxygen partial pressure (pO{sub 2}) in the surrounding environment. Neutron powder diffraction experiments revealed that in a high pO{sub 2} environment the SrFeCo{sub 0.5}O{sub y} material consists of three different phases. The relative concentration of each component phase is dependent on temperature and pO{sub 2} in the surrounding environment. In air, Sr{sub 2}(Fe,Co){sub 3}O{sub y} (236 phase) is the majority phase and consists of >75wt.% of the total, while the perovskite and rocksalt phases account for {approx}20wt.% and <5 wt.%, respectively. However, in a reducing environment, the 236 phase decomposes and converts to perovskite and rocksalt phase at high temperature. In an environment of pO{sub 2} < 10{sup {minus}12.2} atm, the 236 phase is completely converted into perovskite (brownmillerite) and rocksalt phases.

Dense ceramic tubes of the multi-phase mixed ionic/electronic conductor SrFeCo0.5Oy have been synthesized by solid-state reaction, and the stability of its component phases studied using in-situ neutron diffraction over the oxygen partial pressure (pO2) range 10−0.68 to 10−15.0atm at 900°C. This being the likely conditions to which membranes are exposed in operational methane conversion reactors. This material is stable between air and log pO2 = −2.3, with Sr2(Fe,Co)3Oy (236) being the majority phase. When the oxygen partial pressure is lowered, 236 starts decomposing into perovskite and rocksalt phases. The small fraction of remaining 236 rapidly undergoes decomposition at log pO2 = −12.2, leaving only SrFeO2.5 and CoO. Rietveld analysis indicates that the oxygen content of the perovskite phase does not drop below O = 2.5 when log pO2 = −15.0, while there is an indication that CoO is reduced to cobalt metal. This decomposition at low partial pressures may be reversed when the gas is switched back to air, i.e., SrFeO2.5 + CoO re-form Sr2(Fe,Co)3Oy, to an extent that is seemingly dependent on sample and thermal history.

The nonstoichiometry of layered Li 1− x (Ni 0.8 Co 0.2 ) 1+ x O 2 has been controlled by varying the starting composition and preparation temperature. X-ray and neutron powder diffraction has been used to determine the composition of the materials prepared, and the electrochemical properties have been examined.

SrFeCo0.5Oy has been identified as a potential dense ceramic membrane material used for gas separation at elevated temperatures. Neutrons play an important role in the study of such materials, particularly due to the favorable scattering lengths of Fe, Co and O. In-situ neutron diffraction experiments allow these materials to be studied under a wide range of temperatures and oxygen partial pressures. Results indicate very complex behavior of individual phases during synthesis and under operational membrane conditions.