Transport properties of the layered Zintl compound SrZnSb₂

Transport properties of the layered Zintl compound SrZn Sb₂ have been characterized from room temperature to 725 K on polycrystalline samples. SrZn Sb₂ samples were found to be p -type with a Hall carrier concentration of 5× 10²⁰ cm^-3 at room temperature, and a small Seebeck coefficient and electrical resistivity are observed. A single band model predicts that, even with optimal doping, significant thermoelectric performance will not be achieved in SrZn Sb₂. A relatively low lattice thermal conductivity is observed, κ_L ∼1.2 W m-1 K-1, at room temperature. The thermal transport of SrZn Sb ₂ is compared to that of the layered Zintl compounds A Zn₂ Sb₂ (A=Ca,Yb,Sr,Eu), which have smaller unit cells and larger lattice thermal conductivity, κ_L ∼2 W m-1 K-1, at 300 K. Ultrasonic measurements, in combination with kinetic theory and the estimated κ_L values, suggest that the lower κ_L of SrZn Sb₂ is primarily the result of a reduction in the volumetric specific heat of the acoustic phonons due to the increased number of atoms per unit cell. Therefore, this work recommends that unit cell size should be considered when selecting Zintl compounds for potential thermoelectric application.