Effect of Nickel Substitution on Defect Chemistry, Electrical Properties, and Dimensional Stability of Calcium-Doped Yttrium Chromite

Journal Article · Thu Jun 30 04:00:00 EDT 2011 · Solid State Ionics, 193(1):60 - 65

DOI:https://doi.org/10.1016/j.ssi.2011.04.008· OSTI ID:1022428

Yoon, Kyung J; Stevenson, Jeffry W; Marina, Olga A

The effect of nickel substitution on defect chemistry, electrical properties, and dimensional stability of calcium-doped yttrium chromite was studied for use as an interconnect material in high temperature solid oxide fuel cells (SOFCs). The compositions of Y0.8Ca0.2Cr1-xNixO3±δ (x=0-0.15), prepared using the glycine nitrate process, showed single phase orthorhombic perovskite structures over a wide range of oxygen partial pressures (10^-17 atm ≤ pO2 ≤ 0.21 atm). X-ray diffraction (XRD) analysis indicated that most of the nickel ions replacing chromium ions are divalent and act as acceptor dopants, leading to a substantial increase in conductivity. In particular, the conductivity at 900 degree C in air increased from 10 S/cm to 34 S/cm with 15% nickel substitution, and an increase in charge carrier density was confirmed by Seebeck measurements. A point defect model was derived, and the relationship between electrical conductivity and oxygen partial pressure was successfully fitted into the proposed model. The defect modeling results indicated that nickel substitution improves the stability of calcium-doped yttrium chromite toward reduction and suppresses the oxygen vacancy formation, which results in significantly increased electrical conductivity in reducing environment. The electrical conductivity of Y0.8Ca0.2Cr0.85Ni0.15O3±δ at 900 degree C in reducing atmosphere (pO2=10^-17 atm) was 5.8 S/cm, which was more than an order of magnitude higher than that of Y0.8Ca0.2CrO3±δ (0.2 S/cm). Improved stability in reducing atmosphere was further confirmed by dilatometry measurements showing reduced isothermal "chemical" expansion, and the isothermal expansion in reducing atmosphere (pO2=10^-17 atm) at 900 degree C decreased from 0.07% for Y0.8Ca0.2CrO3±δ to 0.03% for Y0.8Ca0.2Cr0.85Ni0.15O3±δ. Based on these results, enhanced electrical performance and mechanical integrity is expected with nickel substitution on calcium-doped yttrium chromite in SOFC operating conditions.

• Research Organization: Pacific Northwest National Laboratory (PNNL), Richland, WA (US)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC05-76RL01830
• OSTI ID: 1022428
• Report Number(s): PNNL-SA-72853; AA2530000
• Journal Information: Solid State Ionics, 193(1):60 - 65, Journal Name: Solid State Ionics, 193(1):60 - 65 Journal Issue: 1 Vol. 193; ISSN 0167-2738; ISSN SSIOD3
• Country of Publication: United States
• Language: English

Related Subjects

30 DIRECT ENERGY CONVERSION
CHARGE CARRIERS
CHEMISTRY
CHROMITES
CHROMIUM IONS
Ceramic Interconnect
DEFECTS
DILATOMETRY
Doped Yttrium Chromite
ELECTRIC CONDUCTIVITY
ELECTRICAL PROPERTIES
GLYCINE
NICKEL
NICKEL IONS
NITRATES
OXYGEN
PARTIAL PRESSURE
PEROVSKITE
POINT DEFECTS
SOLID OXIDE FUEL CELLS
STABILITY
Solid Oxide Fuel Cell
X-RAY DIFFRACTION
YTTRIUM