Crystal structure, microstructure, and electronic transport properties of β-Zn₄Sb₃ thermoelectrics: effects of Zn intercalation and deintercalation

The development of thermoelectric (TE) materials is the key to reduce the use of fossil fuels because they can reuse waste heat to generate electricity via the Seebeck effect. One of the promising p-type TE materials is β-Zn₄Sb₃ which exhibits high TE efficiency. To further improve its TE efficiency, β-Zn₄Sb₃ samples have been prepared by melting and subsequently heating them for different heating time. For the heating time below 150 h, intercalation of Zn atoms into the Zn interstitial (Zn_i) site of β-Zn₄Sb₃ occurs. In addition, the amount of Zn and Zn₃Sb₂ secondary phases decreases, yielding crack-free β-Zn₄Sb₃ samples. For the heating time above 150 h, deintercalation of Zn atoms from the Zn_i site of β-Zn₄Sb₃ occurs. Here, we discuss the evolution of the microstructure and the electronic transport properties, electrical conductivity and Seebeck coefficient (thermopower), during heating from the viewpoint of the Zn intercalation and deintercalation, and this enables us to propose an optimal condition for preparing β-Zn₄Sb₃ with high TE efficiency.