A Study on the Defect Chemistry of Barium-Strontium-Cobalt-Iron-Oxide System
Date
2010-07
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
New York State College of Ceramics at Alfred University. Kazuo Inamori School of Engineering.
Abstract
BSCF, or Ba0.5Sr0.5Co0.8Fe0.2O3-δ, is a well known mixed electronic and ionic
conductor (MEIC) that has been considered as potential cathode for intermediate
temperature solid oxide fuel cells (IT-SOFCs).
Initial 4-point conductivity measurements of Ba0.5Sr0.5CoxFe1-xO3-δ (x = 0, 0.2,
0.4, 0.6, and 0.8) as a function of temperature in air were conducted with Pt-paste
electrodes. Below 400oC, conductivity was thermally activated (Ea = 0.21 – 0.4eV).
Above 400oC, conductivity decreased with increasing temperature, which was attributed
to a decrease in p-type carriers resulting from the formation of oxygen vacancies
associated with the reduction of Fe4+.
The conductivity of BSCF (x = 0.8) as a function of pO2 was also measured.
Above 400oC for pO2 > 0.01atm, the conductivity increased with increasing pO2,
confirming p-type conduction. For pO2 < 0.01atm, a slight increase in conductivity with
decreasing pO2 was observed. To further investigate the possibility of n-type conduction
in BSCF at low pO2, the conductivity and thermopower simultaneously as a function of
temperature and pO2 for five compositions of Ba0.5Sr0.5CoxFe1-xO3-δ (0 < x < 0.8) were
measured. These measurements enable better understanding of the conduction
mechanism of BSCF according to the changes of temperatures and oxygen partial
pressures.
With XPS analysis, as cobalt concentration increases, the trend of peak shifts in
O1s and cations (Co, Fe) has been studied. This study provides the fundamental
background of bonding state on the surface of BSCF ceramics.
Description
Advisory committee members: Alastair Cormack, Scott Misture, Walter Schulze. Dissertation completed in partial fulfillment of the requirements for the degree of Doctorate of Philosophy in Ceramics at the Kazuo Inamori School of Engineering, New York State College of Ceramics at Alfred University
Type
Thesis