BaFe1-xTaxO3-δ – A material for temperature independent resistive oxygen sensors

The sensing properties for resistive oxygen sensors of BaFe1-xTaxO3-δ (BFT) were investigated as a function of the Tantalum content x (0.2 ≤ x ≤ 0.7). Bulk samples were produced by using the mixed-oxide route. X-ray diffraction pattern showed that the perovskite structure was obtained and no second phases were found up to x = 0.5. The electrical conductivity of sintered samples was determined in an oxygen concentration between 1% and 100% in a wide temperature range between 400 and 900 °C. Samples between x = 0.2 and 0.4 are p-type conducting perovskite oxides with almost zero thermal activation. The range, at which the temperature dependency is absolutely zero, shifts with x from 450 °C for x = 0.2 to about 800 to 900 °C for x = 0.4. Specimens of BaFe0.7Ta0.3O3-δ revealed the lowest overall temperature dependency in the entire temperature range. All samples up to x = 0.4 responded fast and reversibly to oxygen concentration changes, even at 400 °C.