Ternary Copper-Based Diamond-Like Semiconductors for Thermoelectric Applications
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1166-N06-07
Ternary Copper-Based Diamond-Like Semiconductors for Thermoelectric Applications Donald T. Morelli and Eric J. Skoug Department of Chemical Engineering & Materials Science Michigan State University East Lansing, MI 48824
ABSTRACT Thermoelectric materials can provide sources of clean energy and increase the efficiency of existing processes. Solar energy, waste heat recovery, and climate control are examples of applications that could benefit from the direct conversion between thermal and electrical energy provided by a thermoelectric device. The widespread use of thermoelectric devices has been prevented by their lack of efficiency, and thus the search for high-efficiency thermoelectric materials is ongoing. Here we describe our initial efforts studying copper-containing ternary compounds for use as high-efficiency thermoelectric materials that could provide low-cost alternatives to their silver-containing counterparts. The compounds of interest are semiconductors that crystallize in structures that are variants of binary zincblende structure compounds. Two examples are the compounds Cu2SnSe3 and Cu3SbSe4, for which we present here preliminary thermoelectric characterization data.
INTRODUCTION Goodman and Douglas investigated the possibility of using substitution to formulate ternary compounds having structures based on binary compounds [1]. They noted that the ternary compound CuFeS2 maintained the same electron-to-atom ratio as the binary zincblende compounds CuBr and ZnS and thus had a structure that closely resembled the binary zincblende structure, known as the chalcopyrite structure. They also noted that Fe could be replaced by a group III element, as the function of the Fe is to donate three electrons. Later studies by Hahn et al. [2] and Zhuze et al. [3] confirmed that compounds of composition AIBIIIX2VI crystallize in the chalcopyrite structure, which they noted was analogous to the binary zincblende structure but with the crystallographic “c” axis doubled ** . Schematically, the chalcopyrite compounds are “built up” from the binary AIIBVI compounds by considering two unit cells of AIIBVI (A2IIB2VI), and replacing the divalent group II atoms with a univalent group I atom and a trivalent group III atom. This simplified view explains the configuration of the chalcopyrite unit cell as essentially two zincblende unit cells stacked on top of each other. B
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A, B, and X represent elements, superscripts denote the groups of the periodic table from which the elements come, and subscripts denote the stoichiometric proportions of each element. This notation will be used throughout the discussion.
Considering three unit cells of AIIBVI and substituting group I and group IV elements on the group II cation sites yields a series of compounds with composition A2IBIVX3VI. Averkieva et al. reported on the structure of such compounds, where AI was copper, BIV was germanium or tin, and XVI was selenium or tellurium [4]. While no silver-containing ternary compounds with the zincblende structure were found, s
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