Off-stoichiometry effect on the thermoelectric properties of the pseudogap Heusler compounds

非化学计量比的Fe_（2-x）V_（1 + x）Al合金由于四元元素的掺杂而获得了大的塞贝克系数和低的电阻率的组合。基于Seebeck系数的价电子浓度（VEC）依赖性，对于富V（x>0）合金，可以获得-180 microV/K的大负值，而从富Fe（x<0）合金获得110 microV/K的良好p型材料。由于V/Al非化学计量比效应，Fe_2 V_（1 + x）Al_（1-x）和Fe_2 V_（1 + x）Tax Al_（1-x）合金具有大的Seebeck系数和低的电阻率，同时它们的峰值温度向400-600 K的高温方向移动。重元素Ta掺杂与非化学计量效应相结合导致热导率的显著降低，使得无量纲优值在400-500 K附近达到ZT=0.22。

A combination of a large Seebeck coefficient and a low electrical resistivity has been obtained for the off-stoichiometric Fe2-xV1+xAl alloys owing to the doping of quaternary elements. On the basis of the valence electron concentration (VEC) dependence of the Seebeck coefficient, a large negative value of -180 microV/K can be obtained for the V-rich (x>0) alloys, whilst good p-type materials with 110 microV/K are derived from the Fe-rich (x<0) alloys. Because of the V/Al off-stoichiometry effect, a large Seebeck coefficient as well as a low electrical resistivity has also been found for Fe2V1+xAl1-x and Fe2VTaxAl1-x alloys, together with a large shift of their peak temperatures towards high temperatures of 400-600 K. The heavy element Ta doping combined with the off-stoichiometry effect leads to a significant decrease in the thermal conductivity, so that the dimensionless figure of merit reaches ZT=0.22 at around 400-500 K.