Solid-state thermoelectric devices are of great interest for researchers in many fields due to their potential to increase the efficiency of electrical power generation as well as provide localized heating or cooling in inconvenient environments. Improving the thermoelectric properties of the materials used in these devices is critical to improve their efficiencies and thus feasibility for niche applications. Unfortunately, several of the underlying materials properties are inversely correlated making the thermoelectric figure of merit difficult to improve. In addition, the performance of traditional semiconducting materials is degraded as the operating temperature is decreased. Thus, a unique approach must be taken to achieve larger thermoelectric figures of merit at low temperatures. The research presented here investigates the use of intermediate valence Yb-based compounds for Peltier cooling in the cryogenic regime. These Yb-based intermediate valence compounds demonstrate large Seebeck coefficients at low temperatures, which is essential to a large figure of merit. The Seebeck coefficient is related to the fluctuating Yb valence, a relationship that is investigated in several compounds and utilized to maximize the thermoelectric figure of merit. Solid solutions are synthesized in order to reduce the lattice thermal conductivity as well as alter the size of the unit cell. Changes in the unit cell volume may contribute to a change in the average Yb valence, and thus be utilized to tune the magnitude and peak temperature of the Seebeck coefficient. By reducing the lattice thermal conductivity and optimizing the Seebeck coefficient, enhancements in the thermoelectric figure of merit can be achieved.
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