Electronic Structure and Thermoelectric Property of Skutterudite CoSb 3
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Electronic Structure and Thermoelectric Property of Skutterudite CoSb3 Kenji Koga, Koji Akai, Kazunori Oshiro, and Mitsuru Matsuura Faculty of Engineering, Yamaguchi University Tokiwadai 2-16-1, Ube 755-8611, Japan E-mail [email protected], Phone/Fax +81 836 85 9622 ABSTRACT Electronic structure of CoSb3 is calculated by means of full-potential linearlized augmented plane wave (FLAPW) method with the generalized gradient approximation (GGA). The calculated band gap of CoSb3 with the consideration of spin-orbit (SO) interaction is 110meV, which is about a half of that without SO interaction. It is found that simple four bands model with the Kane’s nonparabolic valence and conduction bands, two parabolic conduction bands describe calculated electronic structure near band edge very well. Using the simple four bands model, thermoelectric properties are calculated and are discussed. Larger band gap, e.g., Eg=200meV with the microscopic mechanism such as phonon scattering yields a fair agreement with the experiment in a wide range of temperature. INTRODUCTION Skutterudite compound CoSb3 and its filled type compounds such as filled skutterudite CeCo4Sb12, YbCo4Sb12 have attracted very much attention experimentally and theoretically. These materials have features in good thermoelectric property and in large Hall mobility µH, for example µH ~6000cm2/V at room temperatures in CoSb3 [1, 2]. So far there are many experimental and theoretical study in electronic properties in CoSb3. On the other hand, there are few theoretical study of the thermoelectric property in spite of many experimental studies. A theoretical study on the first-principle electronic structure calculation for the skutterudite compounds CoSb3 has been performed by some groups [3-5]. Some authors computed by the FLAPW method without SO interaction. There, Singh-Pickett obtained the energy gap Eg=50meV with the experimental lattice parameters [3]. Noticing that the band structure near Fermi level is sensitive to the position of Sb atom, Sofo-Mahan determined lattice parameters by minimizing of the total energy and obtained Eg=220meV(LDA) and 170meV(GGA) for the different treatment of exchange-correlation effects with the determined lattice parameters [4]. Our previous calculation by the FLAPW-GGA method included the SO interaction and yielded Eg= 42meV with the use of the experimental lattice parameters [5-8]. In this work we start from the determination of the lattice parameters theoretically from the minimization of the total energy with the consideration of SO interaction. Then by using the determined lattice parameter we calculate electronic structure. It will be found that simple four bands model can express the band edge states very well. Using the simple four bands model, thermoelectric property, i.e., the Seebeck coefficient is calculated and is discussed. Self-consistent calculation and electronic structure The skutterudite structure CoSb3 has the bcc (body centered cubic) lattice and the space group Im3, and has an unique features in larg
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