High-temperature order/disorder transition in the thermoelectric Cu 3 SbSe 3
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Eric Skoug and Donald Morelli Department of Chemical Engineering and Materials Science, Michigan State University, East Lansing, Michigan 48824
Hsin Wang, Wallace D. Porter, E. Andrew Payzant, and Edgar Lara-Curzio Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 (Received 15 December 2010; accepted 7 February 2011)
We report the results of an investigation on the structural evolution of a potential new thermoelectric material, Cu3SbSe3, as a function of temperature from 25 to 390 °C. From high-temperature x-ray diffraction data, the refined lattice parameters were seen to change nonlinearly, but continuously, with temperature, with an increased rate of thermal expansion in the a and b lattice parameters from around 125 °C to 175 °C and negative thermal expansion in the c axis from around 100 °C to 175 °C. Crystallographic charge flipping analysis indicated an increase in the disorder of the copper cations with temperature. This reversible order/disorder phase transition in Cu3SbSe3 affects the transport properties, as evidenced by thermal conductivity measurements, which change from negative to positive slope at the transition temperature. This structural change in Cu3SbSe3 has implications for its potential use in thermoelectric generators. I. INTRODUCTION
Thermoelectric materials enable the direct conversion of heat into electricity and are, therefore, the focus of intensive research and development efforts because of their potential to improve energy efficiency by harvesting waste heat from industrial processes and internal combustion engines.1–3 Thermoelectric generators have already been used to power space probes to the outer solar system and are being investigated for improving fuel efficiency of automobiles by reducing the electrical load on the alternator, if not entirely eliminating it.1 However, the use of thermoelectric generators is limited by the low efficiency of current thermoelectric materials. Thus, there is an ongoing search for new thermoelectric materials that can combine a high Seebeck coefficient and electrical conductivity with low thermal conductivity to maximize the figure-of-merit (ZT) and, therefore, the efficiency of thermoelectric generators. Cu–Sb–Se intermetallic phases are currently being investigated as potential new thermoelectric materials with potential operating temperatures around 230 °C. Several ternary compounds exist in this system, including Cu3SbSe3, Cu3SbSe4, and CuSbSe2. Cu3SbSe3 is of particular interest as its thermal conductivity is very low (,1 W m 1 K 1 at room temperature),4 making it a good candidate for improva)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2011.43 J. Mater. Res., Vol. 26, No. 15, Aug 14, 2011
ing the thermoelectric ZT. The room temperature crystal structure of Cu3SbSe3 is orthorhombic, with Pnma (no. 62) symmetry.5 The atomic structure consists of a threedimensional network of edge-sharing Se tetrahedra. The Cu sits in Se tetrahedra and the Sb sits off-ce
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