The solid solution series Tl(V1−xCrx)5Se8: crystal structure, magnetic and thermoelectric properties

International audience; The crystal structure of single crystalline members of the solid solution series Tl(V1-xCrx)5Se8 (x = 0-1 and Δx = 0.2) was determined and the magnetic and thermoelectric properties of bulk TlV5Se8 were investigated. All compounds crystallize in the pseudo-hollandite-type structure (C2/m) with a nonlinear increase in the unit cell volume due to a simultaneous increase/decrease in the transition metal distances across the edge/face-sharing octahedra. A slight Tl deficiency was found for single crystalline TlV5Se8 and Tl(V0.8Cr0.2)5Se8 as well as for bulk TlV5Se8 according to Rietveld and single crystal structure refinements. The metallic character of bulk TlV5Se8 and its low electrical resistivity compared to poly- and single-crystalline TlCr5Se8 can probably be associated with this probable Tl deficiency. In TlV5Se8, anomalies in the low temperature Seebeck coefficient, i.e. a maximum at T ∼ 14 K and two sign changes at T ∼ 47 K and T ∼ 167 K, were found. Bulk TlV5Se8 is a highly frustrated (f = /TN ≈ 42 K) Curie-Weiss paramagnet ordering antiferromagnetically ( = -1287 K) below TN ≈ 31 K with an effective magnetic moment of μ = 2.68 μB corresponding to V3+. Low-field M(H) measurements revealed the existence of a small ferromagnetic component below TN in bulk TlV5Se8 and, despite the observed spin frustration, no spin glass phase was found in this compound. © 2015 The Royal Society of Chemistry.