Pressure effect on the electronic properties of Bi-Sb alloys

Dutta, Soma and Shubha, V and Ramesh, TG and D'sa, Florita (2007) Pressure effect on the electronic properties of Bi-Sb alloys. In: 10th International Conference on Advanced Materials (IUMRS –ICAM), October 8-13, 2007 , Bangalore, India.

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Abstract

The search for new thermoelectric materials is in the direction of maximizing the dimensionless figure of merit (ZT ) = (S2/k)T, where S is the Seebeck coefficient, C and k are the electronic and thermal conductivities respectively. ZT quantifies the performance of a thermoelectric material and hence it is essential to maximize the power factor S2 and minimize k. Among semimetals and narrow band gap semiconductors, bismuth-antimony alloys have received special attention not only due to their interesting physical features from a fundamental point of view, but also for their importance as engineering materials. Moreover, Bi-Sb alloys are very attractive materials for electronic refrigeration and are reported as the best n-type thermoelectric materials around 80K. The structure of their conduction and valence bands drastically depend on different physical parameters such as alloy composition, temperature, external pressure and magnetic field. In this paper we have studied the behavior of Bi-Sb alloys through electrical resisitivity and absolute thermopower as a function of temperature and pressure for various Sb compositions. According to the phase diagram, the synthesis of Bi-rich BiSb polycrystals by the traditional melting technique is not suitable because it gives large segregation in bismuth. The preparation of polycrystals by powder metallurgy method offers the opportunity to reduce the material weakness due to the fine-grained microstructure obtained by this method. As the thermoelectric performances are much better in homogeneous materials than in inhomogeneous materials, it is necessary to look for a powder metallurgy technique to produce homogeneous polycrystals. The mechanical alloying method has been a powerful method to achieve cost ineffective fast productions in large scale. One of the major aims of this work is to study the influence of the mechanical alloying on the band structure of Bi-Sb narrow band gap semiconductors. Pressure studies have been made with different antimony homogeneity in Bi100-xSbx alloys, with x = 10, 12, 15. It is noted that the pressure plays an important role in modifying the electronic properties, through new electronic states in these materials. Electrical resistivity and thermopower have been measured under quasi-hydrostatic pressure conditions upto 20kbar and temperatures upto 200oC. As S,  and k are related and depend strongly on the detailed electronic and crystal structure, an attempt has been made to describe the behaviour of these properties under pressure and temperature conditions. The important findings of the results will be discussed.

Item Type: Conference or Workshop Item (Paper)
Uncontrolled Keywords: Thermoelectric materials;Bi-Sb alloys;Powder metallurgy
Subjects: CHEMISTRY AND MATERIALS > Chemistry and Materials (General)
ENGINEERING > Electronics and Electrical Engineering
Division/Department: Materials Science Division, Materials Science Division, Materials Science Division, Materials Science Division
Depositing User: Ms. Alphones Mary
Date Deposited: 01 Aug 2011 16:10
Last Modified: 01 Aug 2011 16:10
URI: http://nal-ir.nal.res.in/id/eprint/9780

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