Ni7−δSnTe2: Modulated crystal structure refinement, electronic structure and anisotropy of electroconductivity

Single crystals of Ni7−δSnTe2 were grown during re-crystallization of the presynthesized powder in a two zone furnace. The modulated structure was solved and refined in the (3+2)-dimensional superspace group I4/mmm(0–α0, α00)0.ss.mm with lattice parameters a=3.759(1) and c=19.410(2) Å (measured at 153 K) and image. Satellite reflections observed in the diffraction images can be assigned to the incommensurate modulation vectors q1=da* and q2=db* with d=0.410(1). The composition resulting from X-ray structure refinement is Ni5.81SnTe2. The structure model has been also developed in the orthorhombic (3+1)-dimensional superspace group Immm(α00)00s assuming twinning according to [110], giving thus the composition Ni5.79SnTe2. The origin of the modulation can be attributed to a variation of the occupancy of the Ni(3) site in Ni/Te slabs of the structure. Band structure calculations on a commensurate approximant and single crystal electrical resistivity measurements reveal anisotropic metallic conductivity for this compound.