摘要
在許多Heusler-type化合物的研究中，Fe2VAl和Fe2VGa因具有窄能隙半導體的特性且費米能階EF又位於贗能隙(pseudogap)中，而被歸類為半金屬(semimetal)。西元1996年 Mahan和Sofo在一篇論文1提及到，半金屬性化合物是很好的熱電研究對象。本篇論文即研究以過渡金屬鈮Nb摻雜Fe2VGa形成Fe2V1-xNbxGa合金。在10到300K溫度範圍內量測其電阻率 (ρ)、熱傳導率 (κ)、熱電係數 (S)以及熱電優值 (ZT)。
結果顯示，摻雜Nb於Fe2VGa中導致晶格與聲子間的無序散射增加，進而使樣品熱傳導率有效地下降；且此替代結果也使EF位於贗能隙中的能帶重疊(band overlap)增加，顯著地提升熱電係數及有效地降低電阻率，並且在摻雜量x>0時電阻率由半導體特性轉變成半金屬特性。特別是摻雜量x=0.063時，Fe2V0.937Nb0.063Ga在溫度180K時熱電係數的成長幅度達到最大。最後由實驗結果可知，用來判斷熱電性質優劣的ZT值在Nb摻雜下有大幅地提升。

Abstract
Fe2VAl and Fe2VGa has attracted much interests because electronic structure calculations and NMR study indicated that their should be a nonmagnetic semimetal with a pseudogap in the density of state(DOS) at the Fermi level. As proposed by Mahan and Sofo, in 1911, materials with a sharp DOS feature around EF would be good candidates for thermoelectric applications. We report the effects of partial substitution of Nb onto the V sites of Fe2VGa by measuring electrical resistivity, thermal conductivity, and seebeck coefficient as a function of temperature.
It is found that Nb substitution effectively enhance electronic mobility by enlarging band overlap with doped level and thus causes a dramatic decrease in the electrical resistivity. The magnitude of the Seebeck coefficient gradually increases and attains a maximum value of 85 μVK^(-1) at around 180K for Fe2V0.937Nb0.063Ga. The thermal conductivity is also reduced and a detailed analysis based on the Debye approximation indicates that the extrinsic disorder introduced by Nb substitution in Fe2VGa has a main contribution to the point defect scattering. While the thermoelectric performance improves with the partial substitution of Nb, the largest figure-of-merit(ZT) value among these presently investigated alloys still an order of magnitude than the conventional thermoelectric materials.

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