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Environment sensitive electrical conductivity of zirconium titanate ceramics

Porous ceramic humidity sensors are known for superior sensing properties compared to other materials because of their high mechanical strength, chemical resistance and thermal stability. The main mechanisms for humidity detection are either the physical adsorption of water molecules at the surface or water condensation in mesopores of the porous ceramics. The relationship between the structure and electrical properties of ZrTiO4 ceramics sintered at different temperature (1100, 1200, 1300 and 1400 oC) have been investigated by X-ray powder diffraction (XRD), Scanning Electron Microscopy (SEM) and DC conductivity measurements. The DC conductivity,  DC, was measured in air and nitrogen atmosphere and temperature range from 30 to 230 oC with the heating rate of 5 oC min-1. The measurements were performed using a DC bias of 100 V and the resulting current was measured using electrometer. ZrTiO4 ceramics sintered at 1100, 1200 and 1300 °C exhibited significant difference in σ DC measured in air and nitrogen indicating ability of humidity sensing. For ceramics sintered at 1100 oC extremely high sensitivity is related to the presence of open micropores and multiphase composition (rutile TiO2, m ZrO2 and ZrTiO4). This ceramics has low crystallite and grain size and therefore large active surface for water adsorption which is reflected in high electrical conductivity. Increase in sintering temperature to 1200 and 1300 °C results in formation of single phase ZrTiO4 ceramics with larger grain size, which decreases the amount of adsorbed water and consequently decreases the electrical conductivity. Beside that, significant number of closed pores observed in ceramics sintered at 1300 °C does not allow water vapour to pass easily through the structure that decreases the water molecule adsorption and humidity-sensitivity. In contrast to the porous ceramics, the electrical conductivity of sample sintered at 1400 °C is independent on atmosphere due to low porosity and the presence of only completely closed pores.

zirconim titanate ceramics; electrical conductivity

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