期刊
JOURNAL OF MATERIALS CHEMISTRY A
卷 3, 期 7, 页码 3602-3611出版社
ROYAL SOC CHEMISTRY
DOI: 10.1039/c4ta05247a
关键词
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资金
- JSPS KAKENHI [25820334]
- I2CNER by World Premier International Research Center Initiative (WPI), MEXT, Japan
- U.S. Department of Energy [DE-SC0002633]
- Grants-in-Aid for Scientific Research [25820334] Funding Source: KAKEN
- U.S. Department of Energy (DOE) [DE-SC0002633] Funding Source: U.S. Department of Energy (DOE)
The thermochemical expansion behavior of the mixed ionic and electronic conducting perovskite SrTi1-xFexO3-alpha (x = 0.05, 0.35) was characterized to evaluate its potential stability in operating electrochemical devices and to quantify the coupling between oxygen stoichiometry changes and lattice expansion in this material. Changes in oxygen stoichiometry and dimensions of dense specimens were measured using thermogravimetric analysis and dilatometry, respectively, over a range of temperatures up to 1000 degrees C and oxygen partial pressures down to 10(-4) atm, both under steady-state conditions and during thermal or oxygen activity excursions. The separate isothermal chemical expansion and iso-stoichiometric thermal expansion contributions to overall expansion were thereby deconvoluted. For x = 0.35, the isothermal coefficient of chemical expansion (CCE) was found to increase with increasing temperature (CCE = 3.0(3) x 10(-5) x T + 1.9(2) + 10(-2); T is in degrees C), while the iso-stoichiometric coefficient of thermal expansion (CTE) increased with increasing oxygen deficiency (CTE = -3.00 x 10(-5) x delta + 1.44 x 10(-5), per degrees C, where delta = x/2 - alpha). From these relationships, and the measured change in oxygen stoichiometry upon heating, the overall thermo-chemical expansion during heating in air was successfully modeled. The effective size of a vacant anion site was also estimated as a function of temperature from the measured CCEs and found to be comparable to that of an occupied anion site at high temperatures (>= 900 degrees C). For x = 0.05, the changes in oxygen stoichiometry and expansion were smaller over a given temperature or oxygen partial pressure range, though the CCE appeared to be larger than for x = 0.35. Greater charge localization may be responsible for the higher CCE of the sample with the lower Fe content.
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