The influence of intralayer structural distortions on the electrical and magnetic properties of V_1+xMo_2-xS₄ (0 ≤ x ≤ 2)

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 Cc a ˜ 11.8, b ˜ 6.5, c ˜ 12.8 Å, ß ˜ 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, ß ˜ 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.