Thermoelectricity of two-phase mixtures, each with a different type charge carrier, p-NiO/n-ZnO

The relevance of the simple mixing rule for thermopower to a heterogeneous, two-phase mixture, each with different types of charge carriers was considered. The thermopower of p-NiO/n-ZnO two-phase mixtures with an artificial series or parallel configuration and a real polycrystalline configuration as a function of the mixture composition, temperature, and microstructure was examined. It was found that the mixing rule is generally valid for mixtures with the minority phase along grain boundaries. The anomalous, repetitive transitions from n-to-p-to-n-type with increasing temperature are attributed to alternations of the predominant conduction paths with temperature. This mixing rule is compared with conventional theories of the effective thermopower of mixtures. 10 refs.