Impedance response of pseudobrookite thick films with a sandwich configuration

We have investigated the impedance response of pseudobrookite thick films screen printed on alumina substrate in the temperature interval from room temperature to 350 °C in the frequency range 100 Hz-1 MHz. Two thick film pastes were made containing starting hematite and anatase nanopowders (in the 1:1 and 1:1.33 molar ratio - containing excess anatase), glass fritt and organic vehicle. A sandwich PdAg electrode structure was obtained by first printing a PdAg electrode, followed by 3 layers of PSB paste and a PdAg electrode on top with a mesh structure. Each layer was sintered at 850 °C in a hybrid conveyor furnace. XRD analysis confirmed the formation of pseudobrookite with an orthorhombic crystal structure. SEM analysis of thick film surfaces and cross sections showed the formation of a porous structure with rod-shaped grains. The impedance response of pseudobrookite thick films, showed a decrease with the rise in sample temperature. It was analyzed using an equivalent circuit reflecting the dominant influence of grain boundaries.