The influence of intralayer structural distortions on the electrical and magnetic properties of V1+xMo2−xS4 (0 ≤ x ≤2)

Abstract

The series of compounds V_1+xMo_2−xS₄ (0 ≤ x ≤ 2) has been prepared and characterised by powder X-ray and neutron diffraction, thermogravimetry, SQUID magnetometry and electrical transport measurements. Materials with x ≤ 0.50 adopt a distorted variant of the Cr₃S₄ structure (space group Cca ≈ 11.8, b ≈ 6.5, c ≈ 12.8 Å, β ≈ 114.8°) in which there are triangular clusters of cations within a dichalcogenide unit. At higher levels of vanadium incorporation, the phases crystallise in the space group C2/m (a ≈ 12.8, b ≈ 3.3, c ≈ 5.9 Å, β ≈ 114.9°) and the cations within the dichalcogenide slab form zigzag chains, with an intrachain cation–cation separation of ca 2.8Å. The change in the nature of the cation clustering occurs at a composition where there is a transition from semiconducting (x ≤ 0.50) to metallic (x > 0.50) behaviour. Magnetic measurements reveal that paramagnetism is observed over the whole composition range. The measured Curie constants suggest a magnetic moment associated with the cations in the ordered defect layer only and indicate a significant degree of electron delocalisation.