Study of Phase Stability and Electric Conductivity of Er2O3-Nb2O5 Co-doped Bi2O3 Electrolyte
Date Issued
2011
Date
2011
Author(s)
Chou, Tung
Abstract
Er- and Nb- co-doped Bi2O3 materials (abbreviated as ENSB) with fluorite structure show a great potential to be applied as the electrolyte of intermediate temperature-solid oxide fuel cell (IT-SOFC). The colloidal process was used to prepare well-mixed green bodies and sintered at 870oC for 16 hr to get homogenous and dense ENSB samples. The phase stabilization, electrical conductivity, long-term test, and ionic transference number of ENSBs were studied.
This study investigated the effects of dopant ratio Er/Nb, minimal total doping concentration (TDC) on several interesting electric conductive properties. The TDC can be decreased to 10 mol% which is still able to stabilize δ-Bi2O3 in short term. However, when the concentration is lower than 10 mol%, tetragonal β-Bi2O3 appears after cooling. Additionally, an abnormal lattice contraction behavior of the δ-phase was observed in the ENSB. TEM and micro-beam EDS were carried out to analyze the composition around the grain boundaries. No significant segregations of the dopants were found around the grain boundaries.
6.7E3.3NSB (6.7 mol% Er2O3 and 3.3 mole% Nb2O5 co-doped stabilized Bi2O3) exhibited best conductivity of 0.351, 0.209, and 0.116 Scm-1 at 500oC, 600oC and 700oC, respectively, which were measured by 2-probes DC method. The 10E5NSB presents the best phase stability and stable conductivity of 1.6x10-2 Scm-1 after annealing at 650oC for 300 hr. The DTA, TEM, SEM and XRD results demonstrated the degradation of conductivity of 10E5NSB at 650oC, which was controlled by γ-phase formation, not by oxygen vacancy-ordering. The ionic transference number of ENSB measured by EMF method is greater than 0.9 at 600oC to 700oC. High transference number implies high ionic conductivity of ENSB materials.
Subjects
Bi2O3
SOFC
conductivity
fluorite
ionic transference number
annealing
Type
thesis
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