Crystal Growth of Ternary and Quaternary Alkali Metal Bismuth Chalcogenides Using Bridgman Technique
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CRYSTAL GROWTH OF TERNARY AND QUATERNARY ALKALI METAL BISMUTH CHALCOGENIDES USING BRIDGMAN TECHNIQUE Theodora Kyratsi[1], Duck-Young Chung[1], Kyoung-Shin Choi[1], Jeffrey S. Dick[2], Wei Chen[2], Ctirad Uher[2] and Mercouri Kanatzidis[1] [1] Dept. of Chemistry and Center of Fundamental Materials Research, Michigan State University, East Lansing MI 48824-1322 [2] Dept of Physics, University of Michigan, Ann Arbor MI 48109
ABSTRACT Our exploratory research in new thermoelectric materials has identified the ternary and quaternary bismuth chalcogenides β-K2Bi8Se13, K2.5Bi8.5Se14 and K1+xPb4-2xBi7+xSe15, to have promising properties for thermoelectric applications. These materials have needlelike morphology so they are highly anisotropic in their electrical and thermal properties. In order to achieve long and well-oriented needles for which, consequently, the best thermoelectric performance is expected, we developed a modified Bridgman technique for their bulk crystal growth. The preliminary results of our crystal growth experiments as well as electrical conductivity, Seebeck coefficient and thermal conductivity for the compounds obtained from this technique are presented.
INTRODUCTION Exploratory work in the area of thermoelectric materials identified certain new systems as possible new candidates for thermoelectric applications, provided they could be optimized to give high figure of merit ZT. Our own investigations revealed βK2Bi8Se13 to be a promising material with very low thermal conductivity and high power factor [1-5]. Often this compound grows along with K2.5Bi8.5Se14 the potential of which as a thermoelectric material has not been fully investigated yet. These compounds are closely related in composition and structure and are prepared by similar preparation methods. Another interesting new system is K1+xPb4-2xBi7+xSe15 [6], which is much less investigated, but it is neverless promising because of its very low thermal conductivity. In order to learn more about stability of these compounds and their growth habits as well as to begin to evaluate their potential for thermoelectric applications, we decided to undertake large crystal growth studies. The initial results of these efforts are presented here. Most of ternary and quaternary bismuth chalcogenides have needle-like morphology so they are highly anisotropic. Because of this anisotropy, it is important to be able to control the orientation of growing crystals. In this work, we developed a modified Bridgman technique to grow large oriented ingots of the compounds K2Bi6.4Sb1.6Se13, K2.5Bi8.5Se14 and K1.25Pb3.5Bi7.25Se15, in order to be able to explore the thermoelectric properties in various crystal directions.
Z8.8.1 Downloaded from https://www.cambridge.org/core. Access paid by the UCSB Libraries, on 11 Mar 2020 at 23:28:40, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1557/PROC-626-Z8.8
RESULTS AND DISCUSSION K2Bi8Se13 [4], K2.5Bi8.5Se14 [4] and K1+XPb4-2XBi7+XSe15 [6] are anisotropic
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