HIGH-TEMPERATURE IMMITTANCE RESPONSE IN ANATASE-BASED SENSOR MATERIALS

The ac small-signal electrical response of anatase-based sensors is examined at elevated temperatures (400 degrees C less than or equal to T less than or equal to 900 degrees C) via lumped parameter/complex plane analysis (LP/CPA). The ac data, monitored in the frequency range 5 Hz less than or equal to f less than or equal to 13 MHz, are used to establish the role of microstructures on the resulting electrical behavior in these polycrystalline materials. Two semicircular relaxations, observed in the impedance plane, are attributed to the low-frequency related grain boundary and high-frequency related grain response. The grain-boundary response is difficult to quantify at elevated temperatures via LP/CPA and dc measurements. The electrical path homogeneity is examined via the presence of the depression angle which remained nearly invariant in the range of measurement temperatures. These features are discussed and compared with the results obtained at room temperature.