Pseudogap Formation and Thermoelectric Properties of Heusler-type Compounds

通过掺杂或非化学计量比的方法，Fe_2VA_1的热电势有望得到很好的提高，这是因为赝能隙两侧的态密度都急剧上升。本文研究了Fe2VAl基合金的Seebeck系数和电阻率随温度的变化关系，以及室温热导率的测量，以阐明掺杂对热性质和输运性质的影响。的塞贝克系数的组成变化福尔斯在一个通用的曲线，不考虑掺杂元素，当绘制对价电子浓度（VEC），而不是掺杂元素的组成。掺杂的净效应最有可能导致费米能级从赝能隙的中心区域明显偏移，而不会以任何必要的方式改变能带结构。由于重原子的取代大大降低了晶格热导率，因此无疑有利于热电材料的发展。重原子的共掺杂也有效地降低晶格热导率，同时保持低电阻率以及大的塞贝克系数。对于VEC=6的Heusler化合物Fe_<2-x>Co_xTiAl，Seebeck系数的组分变化符合赝能隙的情况，即非化学计量比导致费米能级从赝能隙中心区域出现类刚性带移动.低的Seebeck系数可能归因于Fe和Co之间的原子无序

The thermoelectric power of Fe_2VA1 can be expected to be well enhanced by doping or off-stoichiometry, because the density of states rises sharply in both sides of the pseudogap. We have investigated the temperature dependence of the Seebeck coefficient and the electrical resistivity in the Fe_2VAI-based alloys, in addition to the measurement of the thermal conductivity at room temperature, to clarify the doping effect on the thermal and transport properties. The compositional variation of the Seebeck coefficient falls on a universal curve, irrespective of the doping elements, when plotted against the valence electron concentration (VEC), instead of the composition of the doping elements. The net effect of doping is most likely to cause an appreciable shift of the Fermi level from the central region in the pseudogap without modifying the band structure in any essential manner. The substitution of heavy atoms certainly acts in favor of the development of thermoelectric materials because of a substantial reduction of the lattice thermal conductivity. Co-doping of heavier atoms is also effective to reduce the lattice thermal conductivity while retaining the low electrical resistivity as well as the large Seebeck coefficient. For the Heusler compound Fe_<2-x>Co_xTiAl with VEC=6, the compositional variation of the Seebeck coefficient is in line with a pseudogap scenario where the off-stoichiometry causes a rigid-band-like shift of the Fermi level from the central region in the pseudogap. The low Seebeck coefficient may be attributed to an atomic disorder between Fe and Co