| Summary: | 碩士 === 國立東華大學 === 應用物理研究所 === 96 === Among the group of semimetallic Heusler type compounds with the general formula X2YZ, much interest has been shown on Fe2VAl alloys as a result of their unusual electronic properties. It is suggested that the narrow gap semiconductors and semimetals like Fe2VAl and Fe2VGa with EF located in the pseudogap may be a potentially viable candidate as a good thermoelectric material if appropriate tuning of the electrical and thermal transport properties can be achieved by changing the composition and/or constituent elements and/or preparation conditions. In this thesis, we have studied the effect of partial replacement of Ga by Ge on the electronic properties of Fe2VGa1-xGex alloys by means of electrical resistivity (r), Seebeck coefficient (S) and thermal conductivity (k) measurements from 10 - 300 K.
Upon Ge substitution, the electrical resistivity of Fe2VGa1-xGax alloys show a decreasing tendency with a smooth evolution from semiconducting-like to semimetallic-like with the sign reversal in the temperature coefficient of resistivity (TCR) around x = 0.05, where as lattice thermal conductivity shows only a moderate decrease. The observed variations in S have been attributed to the composition dependent rigid band-like shifting of the Fermi level. Among the presently investigated Fe2VGa1-xGax alloys, a considerable enhancement in ZT for Fe2VGa0.9Ge0.1 compound at intermediate temperatures was noticed.
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