Initial Defect Model of Gas Sensitive BaFe1-xTa xO3-δ Films

Titelangaben

Bektas, Murat ; Stöcker, Thomas ; Hagen, Gunter ; Moos, Ralf:
Initial Defect Model of Gas Sensitive BaFe1-xTa xO3-δ Films.
2017
Veranstaltung: Solid State Ionics 21 , 18.-23.06.2017 , Padua, Italy.
(Veranstaltungsbeitrag: Kongress/Konferenz/Symposium/Tagung , Vortrag )

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Abstract

The thermopower, also known as Seebeck coefficient, allows to determine constants for defect chemical models of semiconductor materials since it is a measure for the charge carrier concentration. The Seebeck coefficient neither depends on the geometry nor on the morphology of the material, like the often investigated conductivity. Resistive high temperature oxygen sensors are discussed for many industrial applications. Preferably, an oxygen sensor should respond only to changes in the oxygen partial pressure but not to temperature variations. BaFe0.7Ta0.3O3-δ is known as a temperature independent conductometric oxygen sensor material with perovskite crystal structure. The present work considers the thermopower as well as the electrical conductivity of BaFe1-xTaxO3-δ for x in the range of 0.1 to 0.5 (BFTx). Seebeck coefficient and conductivity were measured simultaneously between 400 and 900°C under varying oxygen partial pressures from 10-20 to 1 bar. BFTx fine powders have been prepared by conventional mixed-oxide route and were calcined at 1350°C. Crystal structure and phase purity were investigated by X-ray diffraction. BFTx thick-films have been successfully deposited by the novel Aerosol Deposition Method (ADM) at room temperature on a special transducer. Both, thermopower and electrical conductivity, of samples with tantalum contents between x=0.2-0.3 show almost no temperature dependency but depend strongly on the oxygen partial pressure in the temperature range from 700 to 850°C. N-to-p-type transition was observed in the investigated oxygen partial pressure and temperature range. In contrast to the electrical conductivity, the Seebeck coefficient of all samples decreases with increasing oxygen partial pressure. An initial defect chemical model of BFTx will be presented in this study for the materials that show a temperature independent gas sensing behavior.