Executive Summary : | Energy diversification and multi-level usage have become efficient strategies to address the sustainability and environmental challenges. Thermoelectric (TE) conversion technology is based on the Seebeck effect to accomplish direct TE energy conversion. TE materials confronted with intermittent thermal loads at medium to high temperatures are susceptible to problems owing to thermal stress cracking, resulting in a reduced lifespan. Adding to this, the conventional TE materials have very less energy conversion efficiency, which restricts the application of these materials to a few niche applications. To circumvent these problems, functionally graded TE materials (FG-TEMs) have been developed which possess gradient material properties and have the potential to increase the life of TE devices. The aim of the proposed project is to synthesize functionally graded ZnO using spark plasma sintering (SPS) technique by varying doping concentration, mean grain size along the Z-axis or pressing direction for high-temperature TE applications. An experimental and computational investigation will be carried out to formulate the correlation between the processing conditions, formation of graded microstructure, and the resultant TE output performance and the lifetime of the ZnO materials. The idea will be to reduce the lattice thermal conductivity while maintaining high electrical conductivity and the Seebeck coefficient (‘Phonon Glass Electron Crystal' structure). A functionally graded zinc oxide (ZnO) material with graded grain size distribution will be fabricated using spark plasma sintering (SPS) with a thermal gradient. Zinc oxide (ZnO) has been chosen as a base material with multiple doping concentrations due to its consistent TE characteristics, and potential to be a viable candidate for a TE material in mid-to high-temperature ranges. Moreover, the multiple doping will also help in tuning the bandgap and positioning of the valence and conduction band edges, consequently enhancing the Figure of merit (ZT). The spark plasma sintering (SPS) technique will be used for the densification of the material. This technique helps to provide a good density of the material with limitd particle growth, resulting in more dense and small grain size ZnO-based FGM. In addition to this, a mathematical model will be developed to investigate the performance of FG-TEMs. A numerical/ analytical solution for the temperature distribution and TE efficiency as a function of current density will be obtained. The influence of the controlled gradation of the Seebeck coefficient, electrical resistivity, and thermal conductivity along the length on the energy conversion efficiency of a FG-TEM will be evaluated. The proposed work will contribute to the future design of sophisticated TE devices with enhanced efficiency by employing the concept of functionally graded microstructure. |