Oxygen vacancy-activated thermoelectric properties of ZnO ceramics

Understanding the structural and thermoelectric (TE) properties of a pure material is essential for developing a practical approach to improve its TE performance. This study focuses on the high-temperature TE properties of ZnO ceramics synthesized by the spark plasma sintering (SPS) technique. The analyses of crystallinity and microstructure along with photoluminescence and Raman spectroscopy indicated an increase in oxygen vacancy in the ZnO ceramics with SPS temperature, which resulted in unit-cell shrinkage, lattice modification, grain densification, and TE modification. Specifically, oxygen vacancies were found to be a crucial factor affecting the TE performance of the spark-plasma-sintered ZnO ceramics at temperatures exceeding 773 K. Oxygen vacancies can act as carrier donors when they are ionized, contributing to an increase in electrical conductivity and a decrease in thermal conductivity. Additionally, this study proposes a potential way to engineer native defects in ZnO ceramics by controlling the SPS process.