Thermoelectric Properties of UX₂Zn₂₀ (X = Co, Rh, and Ir) Compounds

Thermoelectric materials have an intrinsic property that allows for conversion between heat energy and electrical energy. This property can be harnessed as society pursues renewable energy sources and more efficient energy usage. However, owing to the relatively low efficiency seen in thermoelectric devices their use is currently very limited. To overcome this challenge, great efforts have been made in the discovery of novel materials and composites with novel structural and electronic properties. Measurements on crystals in the 1-2-20 family (YbTM₂Zn₂₀, TM = Co, Rh, and Ir) have revealed enhanced low temperature Seebeck coefficients [1, 2] which could make them useful materials for thermoelectric devices in cryogenic applications. For these materials, the high figure of merit (ZT) originates from f-electron hybridization and reduced thermal conductivity brought on by the sizeable unit cell and phonon mediated "rattling behavior" within the cage-like lattice. In this work, the effects of chemical substitution on the f-electron hybridization strength and phonon scattering modes will be investigated by replacing Yb with U. We will report on the detailed investigation on the thermoelectric properties of U<i>X</i>₂Zn₂₀ (<i>X</i> = Co, Rh, and Ir) single crystals that were grown in a Zn self-flux.<br/><br/>[1] Mun, et. al. Phys. Rev. B, 115110 (2012).<br/>[2] Wei, et. al. Sci. Adv. 5, eaaw6183 (2019).