BaFe1-xTaxO3-y - a material for temperature independent resistive oxygen sensors?

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Oxygen sensors are required for the control of combustion processes and for breath analysis. The resistive sensing principle, in which the conductivity of the sensing material changes with the oxygen content, can be an alternative to the lambda-probe. Such sensors can be miniaturized very well in ceramic planar technology. Although one has tried to exploit the advantages of planar resistive oxygen sensors, one has failed so far mainly due to the temperature dependence of the sensor signal in combination with long-term instabilities and instabilities against sensor poisoning components and as well as due to a low sensitivity. In the past decade, the p-type conducting system SrTi1 xFexO3-y (STF) has been studied in detail since its conductivity features a temperature independent oxygen concentration dependence in the range of interest. Its behavior has been explained by defect chemistry. A disadvantage, however, is the low sensitivity of STF and the low stability in the exhaust.Almost unknown is the material BaFe1-xTaxO3-y (BFT). Very first preliminary investigations of the applicant confirmed an almost temperature-independent conductivity and, at the same time, a 25% higher sensitivity compared to STF. Moreover, it appears feasible to operate sensors with a suitable tantalum content even down to almost 400 °C and to conserve the temperature-independent characteristic. Hence, one may even build an oxygen sensor which is suitable for mobile breath measurement.The project has two main goals.In one part of the project, which accounts for about 3/4 of the project, we will fundamentally learn more about the material BFT (with a tantalum content between 10 and 50%). This includes determining first defect-chemical constants and electronic transport parameters as well as the estimation of the oxygen diffusion coefficients in BFT by appropriate tests.In an engineering science oriented part of the project (about 1/4 of the project scope) temperature-independent resistive oxygen sensors will be made and characterized in terms of their properties. Here, the behavior against expected sensor poisoning compounds is of interest. In this project part, existing transducer can be used (substrate plus heater, cover and electrodes) so that not too much time has to be spent for that.