Thermal diffusivity and electrical conductivity of ZnO-CuO ceramic composites at high temperatures

In this work, thermal diffusivity and electrical conductivity of CuO-ZnO ceramic composites were studied by using laser flash and two point probe technique respectively. I-V characteristic of samples were obtained at temperatures between 100 °C to 450 °C whereas thermal diffusivity was measured at temperatures between 27 °C to 400 °C. Pure ZnO and CuO-ZnO ceramics were prepared by the dry pressing method using a pressure of 2000 kgcm-2 and sintered at 1000 °C for 3 hours in air. Both thermal and electrical properties are preliminary data for future gas sensor application. The way that the thermal diffusivity behaves towards the change of dopant concentration and different temperatures was investigated. The decreased of thermal diffusivity of pure and composite sample with temperature suggests that the dominant contribution to the thermal diffusivity is due to the thermally enhanced phonon-phonon scattering. It was found that there was increment of 32% of thermal diffusivity from 10 wt% CuO (3.46 x10-6 m2s-1 ) to 40 wt% CuO (4.58 x10-6 m2s-1). Beyond 40 wt% of CuO, a sudden decrease in the thermal diffusivity to 2.59 x10-6 m2s-1 was exhibited. The thermal diffusivity was reduced to 43% as it reaches the CuO composition of 50 wt%. It was found that thermal diffusivity of sample decreased with porosity as evidence in SEM micrograph. The average electrical conductivity of pure ZnO and CuO was 1.134 x 10-2 Ω-1m-1 and 2.577 x 10-2 Ω-1m-1 respectively. The increasing of CuO compositions in CuO-ZnO system had increased the overall electrical conductivity of sample due to the more conductive ZnO/CuO interfaces than that for ZnO/ZnO interfaces. The highest value of electrical conductivity was contributed by sample with 50 wt% CuO (5.906 x 10-2 Ω-1m- 1). Effect of grain size, dopant compositions, density/porosity and changes of free electron concentration has been suggested to be responsible for the variation in thermal and electrical behavior and this was supported by XRD and SEM micrographs.

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