Study Of Electronic Structure And Thermoelectric Performance Of Zn- Sb Alloy System

Zn-Sb alloy system has good prospects due to superior thermoelectric properties, non-toxic. People used a variety of experimental methods to study from the preparation to the thermoelectric properties of Zn-Sb alloy. But the theoretical analysis is not comprehensive, the main factors of the thermoelectric properties are unclear, and the systematic research of theoretical aspects are still lacking.For the study of the electronic structure of Zn-Sb alloy system(including Zn Sb, Zn4Sb3), the method of first-principles based on Density Functional Theory(DFT) was used, and the electronic structure, the transport and thermoelectric properties were calculated. Firstly the WIEN2 k package was utilized for the self-consistent calculation of the crystal structure to get energy bands, density of states, charge density and electrical characteristics et al. Then we calculated the transport and thermoelectric properties of materials with the Boltz Tra P code based on Boltzmann transport theory, and obtained the Seebeck coefficient, thermal conductivity, conductivity, and the thermoelectric figure of merit.The results showed that Zn Sb is a kind of indirect bandgap semiconductor with the position of the top of valence band and the bottom of conduction band deviating the point of X and Z, respectively, and has a bandgap about 0.35 e V, more closely to the experimental value of 0.5e V. Zn and Sb atoms form a irregular diamond chain structure, in which the ionic bond and covalent bond exist simultaneously. Seebeck coefficients increased first and then decreased as the temperature increases. When the carrier concentration is 1019cm-3, S acquired a maximum value of approximately 196μV/K at 400 K, close to the experimental value of 200μV/K. ZT value increased first then decreased also as the carrier concentration increased which was consistent with the trends of experimental determination, and has its maximum value 0.72 approximately at 300 K when carrier concentration is 1019cm-3.We calculated the electronic structure and thermoelectric properties of four most likelyβ-Zn4Sb3 structure(Full occupied model, Mayer model, Vacancy model and Interstitial Zn atom model). The results showed that the atom ratio was not strictly integer ratio since the difference of the atom occupation probability in the four kind of β-Zn4Sb3, while Mayer and interstitial Zn atom models were closer to the actual parameters of the model, and the density value of the latter was more consistent with the experimental value. A small amount of impurity levels was bring in at the top of the valence band of the four structures, which was mainly composed of miscellaneous of p orbital electron states of Zn atoms and Sb atoms, and the electrons in p orbital electron states were the main influence factor. Density of states in the top of valence band was more evenly distributed with only a little less sharp peaks, indicating the relatively strong delocalized property of electrons, the strong expansion of atomic orbital, a smaller carrier effective mass, and relatively good thermoelectric properties. The demonstrated localization near the top of the valence band was mainly derived from the density of states contribution of the p-state orbital electron in Sb atoms. From the calculation of Seebeck coefficient, full model was quite different from the experimental values, Mayer model and interstitial Zn atom model have a smaller difference with the experimental values, but a higher seebeck coefficient existed in the latter model. From the calculation of the thermal conductivity and electrical conductivity, interstitial Zn atom model showed better transport properties than the other three structures with the lowest thermal conductivity and relatively high conductivity at the same temperature. From the point of view of merit, maximum value of the four structures are close to the experimental value, but the Mayer model and interstitial Zn atom model were more consistent with experimental value.