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Title: Order-disorder transitions in gadolinium zirconate: A potential electrolyte material in solid oxide fuel cells

Abstract

Rare-earth, yttrium, and calcium doped zirconates are the materials of choice for electrolytes in solid oxide fuel cells. The dopant in these materials serves not only to stabilized the cubic phase of zirconia, but also to introduce anion defects that presumably increase the ionic conductivity. In order to understand the relationships between anion defect distribution, thermal history and ionic conductivity, the structural properties of gadolinium zirconate, Gd{sub 2}Zr{sub 2}O{sub 7}, have been examined via high-temperature x-ray powder diffraction. Gadolinium zirconate is an ideal material for such a structure-property-processing study: it shows ordering of defects at low temperatures, taking on a pyrochlore structure, and disordering at elevated temperature, taking on a defect fluorite structure. Diffraction experiments, performed as functions of time and temperature, confirmed the transition temperature to lie between 1,500 and 1,550 C. They also revealed that the transformation takes place most rapidly just below the transition temperature, indicating that the ordering process is kinetically constrained at low temperatures. Moreover, x-ray data collected at room temperature from quenched samples were found to be as useful, if not more so, than those collected in situ at high temperature. The latter are affected by thermal scattering, severely compromising data quality.

Authors:
;  [1]
  1. Univ. of Washington, Seattle, WA (United States). Dept. of Materials Science and Engineering
Publication Date:
OSTI Identifier:
162904
Report Number(s):
CONF-950412-
ISBN 1-55899-296-0; TRN: IM9604%%8
DOE Contract Number:
AC05-84OR21400
Resource Type:
Book
Resource Relation:
Conference: Spring meeting of the Materials Research Society (MRS), San Francisco, CA (United States), 17-21 Apr 1995; Other Information: PBD: 1995; Related Information: Is Part Of Materials for electrochemical energy storage and conversion -- Batteries, capacitors and fuel cells; Doughty, D.H. [ed.] [Sandia National Labs., Albuquerque, NM (United States)]; Vyas, B. [ed.] [AT and T Bell Labs., Murray Hill, NJ (United States)]; Takamura, Tsutomu [ed.] [Rikkyo Univ., Tokyo (Japan)]; Huff, J.R. [ed.] [Ballard Power Corp., Albuquerque, NM (United States)]; PB: 463 p.; Materials Research Society symposium proceedings, Volume 393
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; 30 DIRECT ENERGY CONVERSION; ZIRCONIUM OXIDES; ORDER-DISORDER TRANSFORMATIONS; GADOLINIUM OXIDES; SOLID ELECTROLYTE FUEL CELLS; ELECTROLYTES; SAMPLE PREPARATION; HEAT TREATMENTS; TRANSITION TEMPERATURE; X-RAY DIFFRACTION; TEMPERATURE DEPENDENCE; TIME DEPENDENCE; QUENCHING; EXPERIMENTAL DATA

Citation Formats

Meilicke, S., and Haile, S.. Order-disorder transitions in gadolinium zirconate: A potential electrolyte material in solid oxide fuel cells. United States: N. p., 1995. Web.
Meilicke, S., & Haile, S.. Order-disorder transitions in gadolinium zirconate: A potential electrolyte material in solid oxide fuel cells. United States.
Meilicke, S., and Haile, S.. 1995. "Order-disorder transitions in gadolinium zirconate: A potential electrolyte material in solid oxide fuel cells". United States. doi:.
@article{osti_162904,
title = {Order-disorder transitions in gadolinium zirconate: A potential electrolyte material in solid oxide fuel cells},
author = {Meilicke, S. and Haile, S.},
abstractNote = {Rare-earth, yttrium, and calcium doped zirconates are the materials of choice for electrolytes in solid oxide fuel cells. The dopant in these materials serves not only to stabilized the cubic phase of zirconia, but also to introduce anion defects that presumably increase the ionic conductivity. In order to understand the relationships between anion defect distribution, thermal history and ionic conductivity, the structural properties of gadolinium zirconate, Gd{sub 2}Zr{sub 2}O{sub 7}, have been examined via high-temperature x-ray powder diffraction. Gadolinium zirconate is an ideal material for such a structure-property-processing study: it shows ordering of defects at low temperatures, taking on a pyrochlore structure, and disordering at elevated temperature, taking on a defect fluorite structure. Diffraction experiments, performed as functions of time and temperature, confirmed the transition temperature to lie between 1,500 and 1,550 C. They also revealed that the transformation takes place most rapidly just below the transition temperature, indicating that the ordering process is kinetically constrained at low temperatures. Moreover, x-ray data collected at room temperature from quenched samples were found to be as useful, if not more so, than those collected in situ at high temperature. The latter are affected by thermal scattering, severely compromising data quality.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = 1995,
month =
}

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  • A serious concern with present designs of solid oxide fuel cells is the requirement that triple-point junctions exist, sites at which the cathode, electrolyte and oxidizing gas are in simultaneous contact. Only at these junctions can the cathode catalyze the reduction of oxygen into O{sup {minus}2} ions and initiate their subsequent transport through the electrolyte. Enhanced ionic conductivity in the cathode material may increase the surface area over which reduction can take place and relax the triple-point constraint. To this end, the authors have examined the electrical and structural properties of LaCo{sub 1{minus}x}Mg{sub x}O{sub 3{minus}{delta}} materials under various atmospheres. Oxygenmore » ion transport in this and related ABO{sub 3} perovskites takes place via oxygen vacancy migration. They have opted to investigate the effect of Mg doping on the transition metal site in an effort to maintain a significant oxygen vacancy concentration in oxidizing atmospheres (as would be encountered during fuel cell operation) and to isolate the effects of A- and B-site doping.« less
  • It was found that the perovskite type oxide La{sub 1{minus}x}Sr{sub x}Ga{sub 0.8}Mg{sub 0.2}O{sub 3}, exhibits the high oxide ion conductivity over a wide oxygen partial pressure and temperature range. The electrical power generation characteristics of SOFCs where LaGaO{sub 3}-based perovskite type oxide was applied as the electrolyte, were studied. It became evident that the composition of La{sub 0.9}Sr{sub 0.1}Ga{sub 0.8}Mg{sub 0.2}O{sub 3} was the most suitable for the electrolyte of the SOFC, among the LaGaO{sub 3}-based perovskite oxides, and furthermore, Ni, and La{sub 0.9}Sr{sub 0.1}CoO{sub 3} were suitable as the anode and cathode, respectively. The maximum power density of themore » SOFC, which consisted of these materials, attained a value as high as 0.93 W/cm{sup 2} at 1,273 K, though the thickness of electrolyte was as large as 0.5mm. Moreover, the power density of cells was still attained at a value as high as 0.17 W/cm{sup 2} at 973 K.« less
  • The interface of La{sub y{minus}x}Sr{sub x}MnO{sub 3}/YSZ was studied with EPMA after annealing at 1200 C to 1400 C for various times. Typical reaction products (Zirconates) and a diffusion zone of Mn and La in the YSZ were determined using quantitative microanalysis. The chemical reactivity at the interface is dependent on the stoichiometry (y) and the Sr content (x) of the perovskite. An increased Sr content leads to a decreased formation of La{sub 2}Zr{sub 2}O{sub 7} but also to an increased diffusion of Mn oxide into the electrolyte material. A high Sr content (x=0.4) reveals both aspects: the formation ofmore » a La- and Mn-enriched SrZrO{sub 3} layer at the reaction interface, as well as a diffusion of Mn oxide into YSZ.« less
  • Fuel electrode materials for solid oxide fuel cell were investigated from their activities for the electrode reaction and for steam reforming of methane. Mixing of metal oxide with Ni significantly modified the activity for the anodic reaction. Ni-CeOx was effective in promoting anodic reaction, and possessed high activity for steam reforming reaction. Gas phase analysis during power generation of SOFC indicated that steam reforming reaction easily proceeded to supply hydrogen for the electrode reaction for the Ni-based cermets. Extremely low and high steam content resulted in deterioration of the electrode performance. Mixing of large YSZ powder with Ni resulted inmore » fast sintering of Ni, but fine YSZ or CeOx powder with Ni was effective in suppressing sintering of Ni in the cermet.« less