Orientation dependence of transport property and microstructural characterization of Al-doped ZnO ceramics

The correlation between thermoelectric properties and crystallographic texture strengths of Al-doped ZnO ceramics prepared by the high magnetic field alignment method was investigated. The relationship between texture strength and electrical conductivity showed a unique characteristic, in which electrical conductivity increased with increasing texture strength, while the Seebeck coefficient was almost independent of the texture strength. Theoretical calculation indicated that the electrical conductivity was not only a function of crystal orientation but also of grain boundary structures. High-resolution transmission electron microscopy revealed that an interfacial layer or segregation of Al at grain boundaries was not observed; however, the coincidence site lattice such as Σ49 was observed at higher texture strength, suggesting that the unique microstructure was the main cause of these transport differences.