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Temperature-independent
oxygen sensors |
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In collaboration
with the Institute for Materials for Electrical Engineering at the University
of Karlsruhe, we are studying SrTi0.65Fe0.35O3 (STF-35) as a potential
oxygen sensor in automotive exhaust systems. Such resistive sensors are
simple and inexpensive to fabricate, but the sensor response depends on
temperature as well as pO2. STF-35 is highly attractive because of its
unique temperature-independent conductivity above 700 C (Menesklou,
et al, see Ref. below).
We are striving to better understand this fascinating system through
defect chemical analysis and thin film experimentation. From solid-state
physics, we can derive a simple expression for the temperature coefficient
of resistance (TCR) that depends on factors relating to the carrier concentration
and mobility. This insight has led us to understand Fe as having a critical
role in determining the TCR behavior. Indeed, thin film work via Rutherford
Backscattering Spectrometry (RBS) and electrical characterization indicates
a strong correlation between Fe depletion in thin films with the overall
pO2 response. |
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Schematic of the band structure
of the STF system and the variation of the Fermi energy with pO2. The carrier
concentration (red) and mobility (blue) contributions to the total TCR are
also sketched. |
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Related Publications |
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A. Rothschild, W. Menesklou, M.
Lufaso, T. Schneider, S.J. Litzelman, H.L. Tuller, E. Ivers-Tiffee, "The
defect chemistry of SrTi1-xFexO3 solid solutions" Solid State Ionics
(2005), submitted. |
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S.J. Litzelman, A. Rothschild,
H.L. Tuller, "The electrical properties and stability of SrTi0.65Fe0.35O3
thin films for automotive oxygen sensor applications" Sensors and
Actuators B 108 (2005) 231-237. |
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A. Rothschild, S.J. Litzelman,
H.L. Tuller, W. Menesklou, T. Schneider, E. Ivers-Tiffee, "Temperature-independent
resistive oxygen sensors based on SrTi1-xFexO3 solid solutions" Sensors
and Actuators B 108 (2005) 223-230. |
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R. Moos, F. Rettig, A. Huerland,
C. Plog, "Temperature-independent resistive oxygen exhaust gas sensor
for lean-burn engines in thick-film technology", Sensors and Actuators
B 93 (2003) 43–50.
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W. Menesklou, H.J. Schreiner,
K.H. Haerdtl, E. Ivers-Tiffee, "High temperature oxygen sensors based
on doped SrTiO3", Sensors and Actuators B 59
(1999) 184–189.
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