Multi-scale defects in ZnO thermoelectric ceramic materials co-doped with In and Ga

Abstract In this work, several X-ray and nuclear analysis techniques were used to examine ZnO materials co-doped with In and Ga, or IGZO materials. X-ray diffraction analysis, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy revealed multi-scale defects in the materials. A nanoscale secondary Ga2Zn9O12 spinel phase, mesoscale grain boundaries, and atomic-scale lattice defects were detected. The lattice defects included oxygen vacancies, zinc vacancies, and complex defects. Positron annihilation spectroscopy and Doppler broadening spectroscopy provided evidence of interactions between charge carriers and defects sites, which explained the low thermal conductivities of the IGZO materials (κtotal ≈ 3.9 W/mK) at 773 K. This combination of X-ray and nuclear analytical techniques can be viewed as a novel approach for investigating the thermoelectric properties of materials with complex crystal structures that contain atomic-scale voids, nanoscale secondary phases, and mesoscale grain boundaries.