Quaternary Chalcogenide Nanocrystals: Synthesis of Cu 2 ZnSnSe 4 by Solid State Reaction and their Thermoelectric Proper
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Quaternary Chalcogenide Nanocrystals: Synthesis of Cu2ZnSnSe4 by Solid State Reaction and their Thermoelectric Properties Umme Farva and Chan Park Department of Materials Science and Engineering, Seoul National University, Seoul 151-744, Republic of Korea ABSTRACT In this paper, synthesis of Cu2ZnSnSe4 (CZTSe) materials by using simple and costeffective solid state reaction method from the elemental Cu, ZnO, SnO and elemental Se powders are carried out. The SEM images show spherical, non-uniform size with aggregation of nanopowders. The phase separation and thermal analysis of the milled powders suggested that most of the starting powders reacted because of a mechanical alloying effect during milling process. After the solid state reaction at above 500 oC, the nanopowders crystallized into stannite single phase, which are confirm by XRD spectra. The thermoelectric properties of synthesized powder are under study. INTRODUCTION The thermoelectric (TE) devices, allowing the solid-state conversion between thermal and electrical energy, have long been considered a very attractive technology for cooling and waste heat recovery [1, 2]. The ideal TE materials possess low thermal conductivity (κ) with good electrical conductivity (σ) and high Seebeck coefficient (S). Thermoelectric effects arise because charge carriers in metals and semiconductors are free to move much like gas molecules, while carrying charge as well as heat. The best thermoelectrics are semiconductors that are so heavily doped their transport properties resemble metals [3]; allow separating control of σ (electron) and κ (phonons). The chalcopyrite-type semiconductor compounds are known to have a potential for application in photovoltaic energy devices, light-emitting diodes and nonlinear optical devices as well as thermoelectric devices [4-7]. These ternary and quaternary chalcogenide compounds can be designed by various combinations of elements in the vicinity of the group IV element. Such tetrahedrally coordinated semiconductors, for example, defect chalcopyrite, spinel, stannite and famatinite, have been suggested [8, 9]. To examine the possibility of the above semiconductors for useful devices is very important for newer material developments. However, the physical properties of these semiconductor compounds, especially of many quaternary compounds, have been scarcely investigated, because it is quite difficult to obtain the crystals with suitable size and quality as compared with elemental and binary compounds [7, 10]. The Cu-doped quaternary chalcogenide are wide-band gap semiconductor belongs to stannite structure. These materials are p-type transparent conductive materials (TCMs) designed from the concept of two structural/functional units (electrically conducting and insulating). These materials are having excellent TE properties at medium temperatures owing to relatively high S because of wide band gap and low values due to their chalcopyrite structure. Here in we
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present a successful synthesis of Cu2ZnSnSe4 (CZTSe) nanopowders in stannite
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