Thermal Expansion Coefficient of BaCo_1-xNi_xS₂

Abstract

Measurements of the linear thermal expansion coefficient α have been carried out on both polycrystalline pellets and single crystals of BaCo_1-xNi_xS₂, which has a layered structure and exhibits the Mott transition with varying x. In the region of x≤ 0.22, where antiferromagnetic state exists below T_N, α exhibits the finite discontinuity Δα at T_N, as is expected in ordinary cases of second order phase transition. The sign of the discontinuity Δα {≡ α (T_N-0)-α (T_N+0)} changes from positive to negative at x-- 0.07 with increasing x, which can consistently be explained by considering the x-dependence of the electronic structure of this system.