Abstract. The present study is focused in two directions. In the first part,
BaFe(1-x)-0.01Al0.01TaxO3−δ (BFATx) thick films
with a Ta content between 0.1 and 0.4 were manufactured using the novel room
temperature coating method “aerosol deposition” (ADM), and its material
properties were characterized to find the best composition of BFATx for
temperature-independent oxygen sensors. The material properties “Seebeck
coefficient” and “conductivity” were determined between 600 and
800 ∘C at different oxygen partial pressures.
BaFe0.69Al0.01Ta0.3O3−δ (BFAT30) was found out to
be very promising due to the almost temperature-independent behavior of both
the conductivity and the Seebeck coefficient. In the second part of this
study, films of BFAT30 were prepared on a special transducer that includes a
heater, equipotential layers, and special electrode structures so that a
combined direct thermoelectric/resistive oxygen sensor of BFAT30 with almost
temperature-independent characteristics of both measurands, Seebeck
coefficient and conductance could be realized. At high oxygen partial
pressures (pO2 > 10−5 bar), the electrical
conductance of the sensor shows an oxygen sensitivity of m = 0.24 (with
m being the slope in the logσ vs. logpO2 representation
according to the behavior of σαpO2m), while the Seebeck
coefficient changes with a slope of
−38 µV K−1 per decade of pO2 at 700 ∘C. However,
at low pO2 (pO2 < 10−14 bar) the conductance
and the Seebeck coefficient change with pO2, with a slope of
m = −0.23 and −21.2 µV K−1 per decade pO2,
respectively.
Combined resistive and thermoelectric oxygen sensor with almost temperature-independent characteristics