METAL-METAL VERSUS ANION-ANION BONDING IN B31 STRUCTURES

The evolution with x in V1-xTixS of the lattice parameters and magneti c susceptibility are contrasted with the situation for CoAs. The V1-xT ixS system exhibits metal-metal bonding with a transition from the B8( 1) structure of TiS to the B31 structure of VS as the metal-metal bond ing in the basal planes of the B8(1) structure weakens with increasing vanadium concentration. In the transition region, the loss of up to 7 mol % sulfur stabilizes the B8(1) versus the B31 phase. The V1-xTixS system is Pauli paramagnetic. In CoAs, on the other hand, a distortion to B31 symmetry is shown to be due to metalloid-metalloid bonding, an d the compound exhibits antiferromagnetic long-range order below TN = 54 K, but with a weak ferromagnetic component if cooled in a magnetic field.