Oxygen Ion Conductivities of Rhombohedral Phases in the Ba-Sr-Bi Oxide System

1998 ◽  
Vol 548 ◽  
Author(s):  
O.A. Gökcen ◽  
S. Kim ◽  
J.K. Meen ◽  
D. Elthon ◽  
A.J. Jacobson
Keyword(s):  
Rhombohedral Phase ◽  
Polymorphic Transition ◽  
Oxide System ◽  
Sudden Increase ◽  
Ion Conductor ◽  
Temperature Range ◽  
Oxygen Ion ◽  
Ion Conductivities ◽  
Rhombohedral Unit Cell ◽  
Impedance Technique

ABSTRACTThe rhombohedral phase of the Ba-Bi-O system is known to be a good oxygen ion conductor. Previous studies on conductivity of that system have shown that there is a sudden increase in conductivity at the β2-β1 polymorphic transition. Therefore, the high temperature β2 phase is a very good anionic conductor with values up to 10−1-100 S/cm. In the Ba-Sr-Bi-O system, the rhombohedral phase that contains Ba and Sr coexists with BaBiO3. Several specimens of the rhombohedral phase with different [Ba]-[Sr] ratios were synthesized. Electron microprobe analysis was used to determine the chemical composition of each specimen and to ensure that it consisted of a monophasic assemblage. Results of X-ray powder diffraction experiments confirmed that each sample has a rhombohedral unit cell. Oxygen ion conductivities of these materials were measured using the 2-probe AC Impedance technique over the 320-730°C temperature range. In each case, a sudden increase in conductivity indicates temperature range of the polymorphic transition. Exchange of the smaller cation Sr for Ba makes the transition temperature increase almost in a linear manner. Conductivities of all β2 polymorphs at a given temperature are very similar to conductivities of Ba-Bi-O and Sr-Bi-O β2 polymorphs. Conductivities of all β1 polymorphs are also similar. Apparently, the nature of the alkaline earth present has only slight influence on conductivities of these phases.

A Composite Ionic-Electronic Conductor in the (Ca,Sr,Ba)-Bi Oxide System

2000 ◽  
Vol 658 ◽  
Author(s):  
James K. Meen ◽  
Oya A. Gökçen ◽  
I-C. Lin ◽  
Karoline Müller ◽  
Binh Nguyen
Keyword(s):  
Polymorphic Transformation ◽  
Alkaline Earth ◽  
Binary Systems ◽  
Bulk Composition ◽  
Stability Limit ◽  
Rhombohedral Phase ◽  
Ion Conductor ◽  
Electronic Conductor ◽  
Oxygen Ion ◽  
Oxygen Ion Conductor

ABSTRACTThe rhombohedral alkaline earth-bismuth oxide phase, an oxygen ion conductor, does not coexist stably with electronic conductors in any of the three binary systems, Ca-Bi-O, Sr-Bi-O, Ba-Bi-O. A thermodynamically stable composite of a rhombohedral phase that contains Ba and Sr or Ca or both with the electronic conductor BaBiO3 may be synthesized. The rhombohedral phase appears to have complete mutual miscibility of the alkaline earth elements. The composi- tions of rhombohedral phase that coexist with BaBiO3 in the Sr-Ba-Bi ternary system and the Ca- Sr-Ba-Bi quaternary systems are described. The value of ionic conductivity of the rhombohedral phase (at a constant Bi: [Ca+Sr+Ba]) is not dependent on the relative amounts of Ca, Sr, and Ba. The temperature at which the rhombohedral phase undergoes a polymorphic transformation from a low-temperature (2) form that is a weak ion conductor to a high-temperature (β1) form that is a much better oxygen ion conductor. The temperatures of the polymorphic transformation and of the upper stability limit of the rhombohedral phase both depend strongly on Ca: Sr: Ba. The β1 form develops in the Ba-Bi system at the lowest temperatures and at the highest ones in the Ca- Bi system. On the other hand, the Ca-Bi phase has greater thermal stability than its Ba ana- logues. The temperature range over which a useful composite conductor can operate is, there- fore, strongly dependent upon the bulk composition of the system.

Transport Properties And Crystal Chemistry Of Ba-Sr-Bi Oxides

2000 ◽  
Vol 658 ◽  
Author(s):  
Oya A. Gökçen ◽  
James K. Meen ◽  
Allan J. Jacobson ◽  
Don Elthon
Keyword(s):  
Binary Systems ◽  
Polymorphic Transition ◽  
Conductivity Measurements ◽  
Spatial Direction ◽  
Ion Conductor ◽  
Electronic Conductor ◽  
Oxygen Ion ◽  
Oxygen Ion Conductor ◽  
Conduction Plane ◽  
Temperature Ranges

ABSTRACTRhombohedral (R) phases of the binary systems AE-Bi-O (AE = Ca, Sr, Ba) have low temperature (β2) and high temperature (β1) polymorphs and the β1 polymorph is a good oxygen ion conductor. In a previous study, we showed that in the ternary system Ba-Sr-Bi-O, conductivities of polycrystalline R samples are unaffected by Ba:Sr, whereas temperature ranges of the β2↔β1 polymorphic transition are. Recently, we proved that the conductivity of both polycrystalline and single-crystal R samples is sensitive to spatial direction. For single crystals, the conductivity is highest perpendicular to the c-axis. Along the conduction plane, the conductivities are significantly higher than those of polycrystalline R samples; perpendicular to that plane they are significantly lower. The BaBiO3 perovskite (P) phase, predominantly an electronic conductor, has conductivities of 10 to 102 S/cm at 350-800°C in air. Conductivity measurements of the R-P assemblages with different R:P showed that percolation threshold is around 35 volume % P.

The Kinetics of Ordering in Gadolinium Zirconate: an Unusual Oxygen Ion Conductor

1995 ◽  
Vol 398 ◽  
Author(s):  
Sossina M. Haile ◽  
Scott Meilicke
Keyword(s):  
Impedance Spectroscopy ◽  
Pyrochlore Structure ◽  
Fluorite Structure ◽  
Transformation Kinetics ◽  
X Ray Diffraction ◽  
Ion Conductor ◽  
Gadolinium Zirconate ◽  
X Ray ◽  
Oxygen Ion ◽  
Kinetics Of

ABSTRACTGadolinium zirconate, Gd2Zr2O7, undergoes an order-disorder transition at ∼1550°C, transforming from a defect fluorite structure (Fm3m) to a pyrochlore structure (Fd3m). Both cations and anions are ordered in the low-temperature, pyrochlore structure. In order to understand the interplay between anion and cation order parameters and ordering rates, the transformation kinetics of Gd2Zr2O7 have been examined via X-ray diffraction. Gadolinium zirconate is of particular interest because the oxygen ion conductivity of the ordered phase is significantly greatly than that of the disordered phase, in contrast to virtually every other known solid electrolyte. This difference in conductivity has provided a second technique for characterizing the transformation kinetics: in situ A.C. impedance spectroscopy. Results of the X-ray diffraction showed the growth of superstructure peak intensity to follow an apparent (time)½ dependence, rather than that expected from a nucleation and growth model. The impedance spectroscopy measurements, on the other hand, showed the conductivity to increase linearly with time. These results suggest the transition is second order in nature.

A conformational polymorphic transition in the high-temperature ∊-form of chlorpropamide on cooling: a new ∊′-form

2009 ◽  
Vol 65 (6) ◽  
pp. 770-781 ◽  
Author(s):  
Tatiana N. Drebushchak ◽  
Yury A. Chesalov ◽  
Elena V. Boldyreva
Keyword(s):  
Phase Transition ◽  
High Temperature ◽  
Structural Changes ◽  
Molecular Conformation ◽  
Polymorphic Transition ◽  
X Ray Diffraction ◽  
X Ray ◽  
Cell Parameters ◽  
Temperature Range ◽  
Two Phases

Structural changes in the high-temperature ∊-polymorph of chlorpropamide, 4-chloro-N-(propylaminocarbonyl)benzenesulfonamide, C10H13ClN2O3S, on cooling down to 100 K and on reverse heating were followed by single-crystal X-ray diffraction. At temperatures below 200 K the phase transition into a new polymorph (termed the ∊′-form) has been observed for the first time. The polymorphic transition preserves the space group Pna21, is reversible and is accompanied by discontinuous changes in the cell volume and parameters, resulting from changes in molecular conformation. As shown by IR spectroscopy and X-ray powder diffraction, the phase transition in a powder sample is inhomogeneous throughout the bulk, and the two phases co-exist in a wide temperature range. The cell parameters and the molecular conformation in the new polymorph are close to those in the previously known α-polymorph, but the packing of the z-shaped molecular ribbons linked by hydrogen bonds inherits that of the ∊-form and is different from the packing in the α-polymorph. A structural study of the α-polymorph in the same temperature range has revealed no phase transitions.

Microstructure and Property Study of La2Mo1.5W0.5O9/Ag Composites

2010 ◽  
Vol 663-665 ◽  
pp. 620-624
Author(s):  
Chun Li ◽  
Da Li ◽  
Qian Feng Fang
Keyword(s):  
Solid State Reaction Method ◽  
Second Phase ◽  
Doping Amount ◽  
Conventional Solid State Reaction ◽  
Single Phase Sample ◽  
Ion Conductor ◽  
Oxygen Ion ◽  
Direct Current Conductivity ◽  
Oxygen Ion Conductor ◽  
Sample Density

Based on the oxygen ion conductor La2Mo1.5W0.5O9, a series of Ag2O doped samples La2Mo1.5W0.5O9/Ag were prepared with conventional solid-state reaction method. The effects of Ag2O doping on the microstructure and electrical conductivity have been investigated by XRD, FESEM and direct current conductivity measurements. With the increase of Ag2O doping, the grain was further refined and compacted, meanwhile, Ag diffusion distribution in the form of second-phase appear at grain boundary. The sample density and conductivity also gradually increased with the increasing of doping amount. The conductivity of the composite specimen La2Mo1.5W0.5O9 /Ag has a great enhancement when the concentration of Ag2O is around 27 wt%, which is eight times higher than that of the single-phase sample.

Sign in / Sign up

Export Citation Format

Share Document