Melt Spinning Preparation of Bismuth Telluride and Partially Alloying with IV-VI Compounds for Thermoelectric Applicatio
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1044-U04-01
Melt Spinning Preparation of Bismuth Telluride and Partially Alloying with IV-VI Compounds for Thermoelectric Application Harald Boettner1, Dirk Ebling1, Alexandre Jacquot1, Uta Kühn2, Jürgen Schmidt3, and Harald Boettner1 1 Thermoelectric Systems, Fraunhofer IPM, Heidenhofstr.8, Freiburg, DE-79110, Germany 2 IFW Dresden, Helmholzstr.20, Dresden, DE-01069, Germany 3 Fraunhofer IFAM Dresden, Dresden, DE-01277, Germany ABSTRACT The melt spinning technique (MST) combined with post annealing processes is evaluated for the development of thermoelectric nanocomposites. The evaluated ones are based on two components almost immiscible in solid state but with crystallographic correlation. One is taken from the V-VI-components system and the other one from the IV-VI-components system. This concept was applied to p-(Bi0,2Sb0,8)2Te3 and to p-[(Bi0,2Sb0,8)2Te3]1-xPbTex composites. MST samples of all types were characterised for some structural and thermoelectric properties. All VVI materials are clearly textured after MST and show no deterioration concerning the thermoelectric properties even after subsequent annealing processes. Structural analysis of p[(Bi0,2Sb0,8)2Te3]1-xPbTex composites gave significant hints for oriented precipitates of a IV-VIrich phase incorporated into the V-VI-rich matrix. The thermoelectric figure of merit of the evaluated composites could be enhanced by suitable annealing procedures of both the quenched bulk materials and the melt spin material. INTRODUCTION It is commonly expected that the development of nanostructured material will lead to breakthroughs in the thermoelectric field. One promising approach utilize nanoscale materials [1]. This is known e.g. for ordered epitaxial nanocomposites [2], for various self-ordered composites [3], for composites with coherent precipitates like in LAST-materials [4]. These types can be summarized under the well known concept “phonon blocking electron transmitting” [1] to achieve higher ZT values caused by reduced thermal conductivities. Beside classical technologies [1] for thin film growth of nanoscaled materials, it is mandatory to develop procedures for much cheaper bulk nanocomposites. Mainly two basic methods are described. One is based on mechanical alloying and subsequent sintering of suitable mixtures [5], the other one is based on rapid quenching of homogenous melts of constituents with extended miscibility gaps in solid state, forming nanoscaled, partially crystallographic ordered precipitations [6-10]. In [11, 12] Nurnus, Böttner et al reported about successful IV-VI /V-VI heteroepitaxy of PbTe/Bi2Te3 and PbSe/Bi2Te3 nanoscale multi-layers. So it is consequent, that IV-VI and V-VI mixed systems were recently examined for their capability to compose selforganizing bulk nanocomposites as a new topic for thermoelectric material [13, 14]. According to [15] IV-VI and V-VI compounds have crystallographic correlation between the 111-plane of the IV-VI compound and the 00L-plane of the V-VI compound. Four different phase diagrams were published
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