Thermoelectric Studies of the Zinc-Antimony Phases

Abstract

This dissertation is dedicated to investigating the thermoelectric properties of the Zn – Sb phases and particularly the Zn13Sb10 material, which was shown to achieve a high ZT (1.3 at 670K) in 1997. The Zn13Sb10 material (known as “Zn4Sb3”) was then extensively studied as a potential thermoelectric material. The Zn13Sb10 materials, however, were not widely adapted in thermoelectric applications. A new synthetic procedure was developed to synthesize phase-pure Zn13Sb10 materials in this thesis, thus allowing a robust characterization of the Zn13Sb10-based materials. This work aims to improve the thermoelectric performance of the Zn13Sb10- based materials by substituting foreign elements into the structure of the Zn13Sb10 phase, at the same time characterize and navigate the synthesis-property-composition relationship of the doped Zn13Sb10 materials. On the other hand, some relative Zn–Sb phases such as the α- and β-Zn3Sb2 were also studied in attempt to complete the characterizations of all Zn–Sb phases stable at room temperatures. The ZnSb phase, another well-studied Zn–Sb material, was investigated in coherence with the Zn13Sb10 materials to understand the effects to transport properties brought by the same atom replacement in the two systems. This was realized in the form of a comparison between the (Zn,Cd)Sb and (Zn,Cd)13Sb10 solid solution series. Materials studied in this work were mostly made using the melt and solidification method. Powder and single-crystal X-ray diffractions were employed to characterize samples’ purity and structure determination. Energy-dispersive X-ray Spectroscopy (EDS) was used to determine sample compositions, especially to confirm the presence(s) of dopants in materials in small quantities. Physical properties of materials were measured to evaluate the thermoelectric performances of materials. Computational methods, such as the linear muffin-tin orbital (LMTO) method was used to help understand the transport properties of materials and the electron localization function (ELF) method to analyze the bonding natures between atoms.