Crystal Structure and Thermoelectric Properties of the Incommensurate Chimney–Ladder Compound VGeγ (γ ~1.82)
A single-phase sample of a Nowotny chimney–ladder phase known as V17Ge31 has been prepared and its modulated crystal structure has been determined by means of a (3+1)-dimensional superspace approach. As in the case of higher manganese silicides (HMSs) MnSiγ, the compound consists of two tetragonal subsystems of [V] and [Ge] with an irrational c-axis ratio $$\gamma $$γ = $$c_{\rm{V}}$$cV/$$c_{\rm{Ge}} \sim $$cGe∼ 1.82, and hence the structure formula is represented as VGeγ. As expected from the valence electron count estimated from the refined γ, the present germanide exhibits a metallic behavior with the electrical conductivity σ = 6.25 × 103 S/cm and the Seebeck coefficient S = 10.2 μV/K at 900 K. The resulting thermoelectric power factor of $$S^2\sigma $$S2σ = 6.56 × 10-5 W/mK2 and the dimensionless figure-of-merit, ZT, = 3.7 × 10-3 at 900 K demonstrate that the germanide is not a promising thermoelectric material. However, as the determined lattice thermal conductivity is comparable to that of HMSs, thermoelectric properties can be maximized through the partial substitution of V with group 6–8 elements to decrease hole carrier concentration.