Thermoelectric devices provide a reliable, non-toxic, solid-state solution to energy lost as waste heat. However, there are relatively few materials with high efficiency in the mid-temperature regime (200 – 500 °C), where a high thermoelectric figure of merit (zT) material could impact low grade waste heat recovery, such as in industrial processes, and small-scale power conversion, for example in mid-temperature solar thermoelectric generators (STEGs). Yb2-xAxCdSb2 (A = Eu, Ca) is an ideal p-type Zintl phase and a new addition to materials with efficient energy conversion (as indicated by the figure of merit, zT). Yb2-xEuxCdSb2 has potential in the optimal mid-temperature STEG operating range and results in a zT at 523 K of 0.67. The significant zT stems from the high Seebeck coefficient and extremely low thermal conductivity of this material due to its complex phonon dispersion and point scattering by defects. The Yb-Eu system has an optimized thermal conductivity at or below its minimum theoretical value. The synthesis, structure, and bonding of this system will be presented on these new thermoelectric materials that have significant potential for future improvement.