Crystal structure, electrical transport properties and electronic structure of the VFe1−xCuxSb solid solution

The electrical transport properties, crystal structure and electronic structure of the VFe1−xCuxSb solid solution (0 ≤ x ≤ 0.2) were studied. The stability ranges of the limited solubility for these phases were established. All alloys of these solid solutions crystallize with the MgAgAs structure type, space group F43m and the stability range extends up to the VFe0.8Cu0.2Sb composition. All the samples in this series remained n-type in the temperature range from 4 to 400 K. They display metallic resistivity at high temperature, the resistivity passing through a shallow minimum as the temperature decreases. The Fermi level was determined to reside in a sharp d-DOS peak due to Cu located at the conduction band edge. A successive shift of the Fermi level from the gap (in pure VFeSb) to the conduction band (in Cu doped samples) well corresponds to the marked decrease of the electrical resistivity as measured in VFe1−xCuxSb. The decrease of the electrical resistivity and thermopower is discussed in view of the Fermi surface change upon alloying VFeSb with Cu. The electronic structure of VFe0.8Cu0.2Sb in two allotropic phases was also calculated in order to shed light on the cubic-hexagonal transition and the solubility limit.