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Structural and Electrical Characterization of a Novel Mixed Conductor: Ceo<Sub>2</Sub> University of South Carolina Scholar Commons Faculty Publications Mechanical Engineering, Department of 2000 Structural and Electrical Characterization of a Novel Mixed Conductor: CeO2 - Sm2O3 - ZrO2 Solid Solution W. Huang P. Shuk M. Greenblatt M. Croft Fanglin Chen University of South Carolina - Columbia, [email protected] See next page for additional authors Follow this and additional works at: https://scholarcommons.sc.edu/emec_facpub Part of the Applied Mechanics Commons, Materials Chemistry Commons, and the Other Mechanical Engineering Commons Publication Info Published in Journal of The Electrochemical Society, Volume 147, Issue 11, 2000, pages 4196-4202. ©Journal of The Electrochemical Society 200, The Electrochemical Society. © The Electrochemical Society, Inc. [year]. All rights reserved. Except as provided under U.S. copyright law, this work may not be reproduced, resold, distributed, or modified without the express permission of The Electrochemical Society (ECS). The ra chival version of this work was published in Journal of The Electrochemical Society. Publisher’s Version: http://dx.doi.org/10.1149/1.1394040 Huang, W., Shuk, P., Greenblatt, M., Croft, M., Chen, F., & Liu, M. (2000). Structural and Electrical Characterization of a Novel Mixed Conductor: CeO2 - Sm2O3 - ZrO2 Solid Solution. Journal of The Electrochemical Society, 147 (11), 4196 – 4202. http://dx.doi.org/ 10.1149/1.1394040 This Article is brought to you by the Mechanical Engineering, Department of at Scholar Commons. It has been accepted for inclusion in Faculty Publications by an authorized administrator of Scholar Commons. For more information, please contact [email protected]. Author(s) W. Huang, P. Shuk, M. Greenblatt, M. Croft, Fanglin Chen, and M. Liu This article is available at Scholar Commons: https://scholarcommons.sc.edu/emec_facpub/271 4196 Journal of The Electrochemical Society, 147 (11) 4196-4202 (2000) S0013-4651(00)03-078-0 CCC: $7.00 © The Electrochemical Society, Inc. Structural and Electrical Characterization of a Novel Mixed Conductor: CeO2-Sm2O3-ZrO2 Solid Solution W. Huang,a P. Shuk,a,d,* M. Greenblatt,a,z M. Croft,b F. Chen,c,** and M. Liu c,* aDepartment of Chemistry and bDepartment of Physics, Rutgers, the State University of New Jersey, Piscataway, New Jersey 08854, USA cSchool of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia 303320, USA 5 (Ce0.83Sm0.17)12xZrxO22d (x 0 to 0.50) solid solutions were synthesized for the first time by the hydrothermal method. The elec- trical properties of the solid solutions have been studied in air and under reducing conditions. Solid solutions with the fluorite struc- 8 ture were formed in all of the studied range of ZrO2 substitution after calcination at 1500 C. With increasing ZrO2 substitution up to 30 mol %, the electronic conductivity increases under a reducing atmosphere. The (Ce0.83Sm0.17)0.7Zr0.3O22d solid solution has 5 3 221 8 good mixed electronic and ionic conductivity; the total conductivity is 0.42 S/cm at pO2 5.7 10 atm and 700 C with an estimated ionic conductivity of ca. 1022 S/cm. © 2000 The Electrochemical Society. S0013-4651(00)03-078-0. All rights reserved. Manuscript submitted March 17, 2000; revised manuscript received July 7, 2000. Solid electrolytes are key components of solid-state electro- radiation at a 2u scan of 0.58/min. Cell parameters were calculated chemical devices, which are increasingly important for applications by fitting the observed reflections with a least-squares program. in energy conversion, chemical processing, sensing, and combustion XAS measurements.—The X-ray absorption spectroscopy (XAS) control.1-3 Solid electrolytes based on CeO4 also have potential 2 measurements were made in the electron yield and fluorescence applications as structural and electronic promoters of heterogeneous modes15-17 on beam line X-19A at the Brookhaven National Syn- catalytic reactions and oxygen membranes.4-8 chrotron Light Source with double crystal [Si(111)] and monochro- In recent years the CeO -ZrO system has been investigated, 2 2 mater. All spectra were normalized to unity step in the absorption mainly in the context of a “three-way catalyst” technology for the coefficient from well below to well above the edge. treatment of automobile exhausts.9-13 It has been reported that the reducibility of ceria is greatly enhanced when it is mixed with zirco- Electrical conductivity measurement.—The powder samples were 9-13 8 nia to form a solid solution. These results suggest that CeO2-ZrO2 pelletized and sintered at 1500 C for 24 h with a programmed heat- might be an excellent mixed conductor (exhibiting both ionic and ing and cooling rate of 58C/min. The sintered samples were over 95% electronic conductivity). It is the numerous applications of mixed of the theoretical density in all cases, as determined by pycnometry. conductors as oxygen separation membranes, partial oxidation cata- The ionic conductivity of the materials was measured on a sin- lysts, and fuel-cell electrodes that motivated us to investigate the tered ceramic pellet. Silver paste was painted onto two faces of the CeO -ZrO solid solution as a potential mixed conductor. Recently pellets, using GC Electronics paste. The sample was then dried and 2 2 8 we have shown that solid solutions of Ce12xSmxO22x/2 and Cex- fired at 700 C. The ionic conductivity measurements were per- CaxO22x can be hydrothermally prepared in a wide substitution range formed by the complex-impedance method at frequencies ranging of Sm or Ca.14 Our systematic studies showed maximum ionic con- from 0.1 Hz to 20 kHz (Solartron 1280 frequency response analyz- ductivity for the Ce0.83Sm0.17O22d composition. In order to achieve er) on isothermal plateaus 1 h long, in air on heating and cooling appreciable ionic conductivity in the mixed conductor, we have inves- every 25 to 508C up to 8008C. tigated the substitution of Ce0.83Sm0.17O22d with 0 to 50 mol % The electrical conductivity of ceria samples was measured as a 5 ZrO2, i.e., (Ce0.83Sm0.17)12xZrxO22d (x 0 to 0.5) solid solutions. In function of oxygen partial pressure, pO2, and temperature with a this paper we report the results of these studies. four-probe dc technique. A mixture of O2,N2, and H2 gases passed through a water separator, set at 25 to 858C, was used to fix differ- Experimental ent oxygen partial pressures determined from the equilibrium of the 5 Synthesis.—Solid solutions of (Ce0.83Sm0.17)12xZrxO22d (x 0 chemical reactions of the gases. The oxygen partial pressure in the to 0.50) were synthesized by the hydrothermal method as previous- gas mixture was measured by a solid-electrolyte oxygen sensor be- ly reported for the Tb, Sm, and Ca doped ceria solid electrolytes.7,14 fore and after the gasses passed through the closed ceramic cell The appropriate quantities of cerium(III) nitrate hexahydrate where the ceria solid electrolyte sample was placed for the conduc- ? [Ce(NO3)3 6H2O, 99.9% Aldrich], samarium(III) nitrate hexahydrate tivity measurements. The samples were allowed to equilibrate at the [Sm(NO ) ?6H O, 99.9% Aldrich], and zirconium dichloride oxide 3 3 2 set pO2 atmospheres for 24 h before the measurement was taken. hexahydrate (ZrOCl ?6H O, 99.9% Aldrich) were dissolved separate- 2 2 Electrode polarization measurement.—For the electrode polar- ly in water, mixed and coprecipitated with ammonium hydroxide ization measurements, the ceria samples were prepressed uniaxially, at pH 10. The precipitated gels were sealed into Teflon-lined steel then isostatically under 500 MPa. The green densities were about 55 autoclaves and hydrothermally treated at 2608C for several hours. to 58%. The green pellets were sintered at 14008C for 1 h with a pro- The autoclaves were quenched, and the crystallized powder of grammed heating and cooling rate of 58C/min. The sintered samples (Ce Sm ) Zr O (x 5 0 to 0.50) solid solutions were repeat- 0.83 0.17 12x x 22d were over 98% of the theoretical density in all cases. Platinum elec- edly washed with deionized water and dried in air at room temperature. trodes were attached with a commercial electrode process. First a X-ray diffraction.—The powder X-ray diffraction patterns thin Pt film was sprayed on the pellet surface and then sintered at (XRD) of the ultrafine powder samples were obtained with a Scin- 12008C; finally the Engelhard Pt paste was used to optimize the tag PAD V diffractometer equipped with monochromatized Cu Ka electrode properties. The sample was dried in air and fired at 9008C. The impedance measurements were performed with an impedance analyzer SI-1260 (Solartron Instruments) over 0.01 Hz to 1 MHz ** Electrochemical Society Active Member. ** Electrochemical Society Student Member. frequency range on isothermal plateaus 1 h long, in air on heating *d Present address: Rosemount Analytical, Inc., Orrville, OH 44667-0901, USA. every 508C up to 6508C. The inductive error associated with various *z E-mail: [email protected] components of the measurement circuit was evaluated by carrying Downloaded on 2015-03-04 to IP 129.252.69.176 address. Redistribution subject to ECS terms of use (see ecsdl.org/site/terms_use) unless CC License in place (see abstract). Journal of The Electrochemical Society, 147 (11) 4196-4202 (2000) 4197 S0013-4651(00)03-078-0 CCC: $7.00 © The Electrochemical Society, Inc. out measurements in the rig on reference resistances in place of 2 2(mair m ) M sample samples. All the measurements were corrected accordingly. The d 5 [3] m M curve fitting was done with “Zview 2.1b” with different equivalent air O2 circuits. The solid-electrolyte conductivities as well as polarization where m and m represent the mass of the sample in air and reduc- resistances of the applied electrodes were determined directly from air ing atmospheres, respectively, M and M are the molar mass the impedance spectra.
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