Structure And Thermoelectric Properties Of N-type In-Se Based Semiconductors

Ag In Se2 is a kind of I–III–VI2 semiconducting compounds crystallizing in a chalcopyrite structure. There is an inherent Coulomb attraction between charged defects In Ag2+and 2VAg1-(a native defect pair, i.e., metal In-on-Ag anti-sites and two Ag vacancies) in Ag In Se2.Then select element Zn substituting Ag in Ag In Se2, which leads to the formations of the defects Zn Ag1+and Zn In1-as an active donor and acceptor. These defects significantly modify the band structures and transport properties, and have a potential improving the thermoelectric(TE) performance. α - In2Se3 is a kind of semiconducting compounds with a layered structure, Many theoretical calculations indicated that there are 1/3 of the sites of indium atoms being empty, which has a possibility to improve the TE performance. In this work, preparing two groups of materials Ag1-x In Znx Se2(x=0, 0.025,0.05, 0.01), In2-x Znx Se3(x=0.005,0.01,0.02) by using powder metallurgy technology. The results are summarized as follows:1. Fabricating one group of materials Ag1-x In Znx Se2(x=0.025,0.05,0.1), and refined their structures to reveal the occupations of Zn in the lattice sites by using Structure Refinement(GSAS). Through refinement, almost an equal occupation of Zn at In and Ag sites was observed. The ZT of Ag1-x In Znx Se2(x=0.1) has a best performance with ZT value of 1.05± 0.12 at 815 K, much superior than that of intrinsic Ag In Se2.2. Preparing Zn-added In2-x Znx Se3(x=0.005,0.01,0.02) compounds by using the same technology, and analyzed their crystal structures and thermoelectric properties. Analysis reveals that the Zn atoms are intercalated into the van der waals(VDW) spacing between Se-Se layers, but this result needs further verification. The intercalation of Zn facilitates the carrier transport across the VDW gaps, thus enhancing the carrier concentration(n)and mobility(μ). Besides, it distorts the crystal lattice simultaneously, which thereby reduces the lattice thermal conductivity to a certain extent. Measurements revealed that the ZT value reaches 0.75 at x=0.1 and 917 K for the sample with perpendicular to the pressing direction, while that reaches 1.22 along the pressing direction. The maximum ZT value is about 5 times that of intrinsic In2Se3.