Structural, magnetic, and electronic properties of vanadium-substituted nickel chromium sulfide

A series of sulfides NiCr(2-x)V(x)S₄ (0 < x < 2.0) has been synthesized at high temperatures. All products are isostructural with Cr₃S₄ (space group I2/m; a ? 5.9 Å, b ? 3.4 Å, c ? 11.1 Å; ß ? 91.8°) in which octahedral sites between pairs of close-packed anion layers are alternately fully and half occupied. Materials with x < 0.6 are variable-range-hopping semiconductors, whereas those with higher vanadium contents are metallic. The insulator to metal transition at x ? 0.6 is accompanied by a structural distortion, which results in the formation of cation chains in the fully occupied layer. Magnetic susceptibility data indicate that magnetic order initially persists into the metallic phase, disappearing above x = 0.8. Powder neutron diffraction data reveal that the magnetic order involves a doubling of the crystallographic unit cell in both the a and c directions.