Crystal structure, electronic structure and thermoelectric properties of β- and γ-Zn4Sb3 thermoelectrics: a (3+1)-dimensional superspace group approach

Thermoelectric (TE) materiaLs are promising candidates for solving today's energy problem owing to their ability to directly convert waste heat into electricity via the Seebeck effect. One of the most efficient TE materiaLs known is Zn4Sb3. To understand its high efficiency, a novel composite crystaL structure model for 13- and 7 -phases of Zn4Sb3 is constructed using a (3 + 1) -dimensional ((3 + 1)-D) superspace group approach. This (3 + 1)-D model is expressed as [Zn3+,5S19][Sb], with the superspace group of R3m(00)))0s. The [Zn3+,5S19] and [Sb] subsystems have same a- and b -axis Lengths but a different c -axis Length. The (3 + 1)-D model contains four atomic sites: a Zn(1) normal site, an interstitial Zn (Zn;) site and an Sb(1) site in the [Zn3+,5S19] subsystem and an Sb(2) site in the [Sb] subsystem, which is different from a conventional 3D model containing additional Zn; sites. The crystaL structures of 13- and 7-Zn4Sb3 are investigated via powder and synchrotron X-ray diffraction (XRD) measurements. The XRD patterns are weLL analysed by the (3 + 1)-D modeL. The occupancies of Zn(1), Sb(1) and Sb(2) sites are 100%, whereas the Zn; occupancy changes depending on the heating time during the preparation of 13-Zn4Sb3. Moreover, electronic density of states (DOS) of 13-Zn4Sb3 with and without Zn; is caLcuLated based on the (3 + 1)-D modeL, demonstrating a dose relationship between the DOS and the Zn; occupancy. The caLcuLated TE properties, such as Seebeck coefficient, electrical conductivity and power factor, also depend on the Zn; occupancy.