Thermoelectric materials and devices, that can convert heat energy to electrical energy and vice versa, are viable solutions to some energy needs. Compared to conventional power generation systems, their main disadvantage is lower efficiency. The lower efficiency of thermoelectric devices is primarily attributed to the low figure of merit (ZT) of thermoelectric alloys. For power generation applications, high ZT at high temperature is essential. The goal of this project is to develop newer thermoelectric (TE) alloys that have high figure of merit at high temperature. The figure of merit is the key material property that can achieve high heat-to-electricity conversion efficiency. In order to increase the figure of merit, the lattice thermal conductivity and electrical resistivity needs to be lowered while maintaining high thermoelectric power. Alloying the binary thermoelectric alloys leads to disordered unit cell structure thereby reducing the lattice contribution of the thermal conductivity which results in higher ZT. The lattice disorder in the crystal structure can be assessed in terms of increase in entropy change of the TE alloys. Since the newer thermoelectric alloys are typically multi-component alloys, a thermodynamic study of such systems will be investigated to better understand the properties of TE alloys. This research project aims to develop fundamental data (thermodynamic properties, phase equilibria and transport properties) for newer high ZT at high temperature thermoelectric alloys of type ABX and ABX2: where A and B are transition metals (Ti, Nb, Co, Mn) and X is Boron or Silicon. Thermodynamic properties of thermoelectric alloys using solid-state galvanic cell method will be investigated. Gibbs energy of formation of compounds and excess Gibbs energy of mixing will be determined. Phase stability in the alloy systems at different temperatures will be determined. The alloy phases will be characterized using several techniques such as TEM, SEM and XRD. Various transport properties such as thermal conductivity, electrical resistivity and Seebeck coefficient will be determined with already existing experimental setup. Experimental data generated in this study for phase stability, excess Gibbs energy of mixing, Gibbs energy of formation of the compounds, available crystal structural data of the compounds will be used in modeling the phase equilibria of the newer thermoelectric alloys. This work is expected to generate new thermodynamic properties data that can be used in development of newer thermoelectric alloys.
NON-TECHNICAL SUMMARY: The demand for alternative, sustainable energy conversion and power generation is imminent due to the increasing demand for energy, high cost and exhaustion of combustible fossil fuels and the environmental impact of current technology. Thermoelectric materials and devices, that can convert heat energy to electrical energy and vice versa, is a viable solution to the energy needs. Thermoelectric devices offer the advantages of being silent, reliable, and scalable, and having no moving parts. However, compared to conventional power generation systems, their main disadvantage is lower efficiency. The lower efficiency of thermoelectric devices is primarily attributed to the low figure of merit (ZT) of thermoelectric alloys. For power generation applications, high ZT at high temperature is essential. The goal of this project is to develop newer thermoelectric (TE) alloys that have high figure of merit at high temperature. The outcome of this research would improve our fundamental understanding of thermoelectric alloys. Thermodynamic properties and phase equilibria data generated will form a basis for the development of newer thermoelectric alloys. The program would provide a wide variety of expertise (teaching and research), enrichment of scientific knowledge and to instill new creative and critical thinking among students. Integration of research and education at the university will be enhanced, particularly minority students through the proposed research project. With the collaboration of the HBCUs and high schools, the proposed research program will facilitate experience for K-12 students and high school teachers. Fundamental science and newer TE alloys used in efficiently harnessing the waste heat from various high temperature processes will be emphasized. The research results will be disseminated to a wide network of scientific personnel via presentations and publications in relevant journals.
