Metal-Insulator Transition in AxVS2 Compounds

Abstract

The ternary transition metal compounds AlxVS2 (0.25 ≤ x ≤ 0.50) have structures derived from hexagonal CdI2–NiAs with an enlarged 2a0 × 2a0 × 2c0 × (2T) 2a0 × 2a0 × 3c0 × (3T) basic cell alongwith structural distortions. Transport properties are very sensitive to the temperature of preparation. The low temperature annealed (LT) phases show higher conductivity at room temperature than high temperature quenched (HT) phases. On cooling, these metal‐like phases show two different transitions in conductivity, first one around 160 to 180 K giving insulator‐like phases and the second around 30 to 40 K where the resistance shows a sharp decrease on cooling. The phases quenched above 1000 °C give widely different transport and thermoelectric properties depending upon Al concentration with metallic (x = 0.50), insulating (x = 0.33) or semiconducting (x = 0.25) behaviour. The magnetic susceptibility of all these phases shows strong temperature dependence above 80 K. These properties are discussed in terms of localization of carriers on V–V clusters and structural disorder.