Electrical transport measurements and electronic structure calculations on doped half-Heusler FeVSb

Abstract

Structural and electrical transport properties of pure and doped FeVSb half-Heusler phases were investigated from X-ray diffraction, Mossbauer spectroscopy, resistivity and thermopower measurements. The doping elements were Ti, Zr, Mn and Co. Electronic structures calculations of experimental samples were carried out using Korringa-Kohn-Rostoker coherent potential approximation (KKR-CPA) method within the LDA framework. We observed that the room temperature Seebeck coefficient changed from highly negative in FeV/sub 0.98/Mn/sub 0.02/Sb (-190 /spl mu/V/K) to highly positive in FeV/sub 0.85/Ti/sub 0.15/Sb (+140 /spl mu/V/K), being also negative in FeVSb. Except for Fe/sub 0.98/Co/sub 0.02/VSb, all investigated samples exhibit either semiconducting or semimetallic behaviors of resistivity curves. From band structure calculations FeVSb exhibits a narrow band gap (E/sub g/=0.45 eV) at E/sub F/. However, as deduced from the KKR-CPA calculations, a small disorder in FeVSb may substantially modify electronic structure in the vicinity of EF, leading into an energy gap closing. Total energy analysis allowed estimating lattice parameter variation with doping as well as a site preference of substituted atoms in the FeVSb host. Densities of states of Ti, Zr, Mn and Co impurities in FeVSb were computed. The others dopants, Mn impurity in FeVSb form a huge peak in the gap, which can be responsible for unusual transport properties of this system.