Structural Studies on the Quasi Two-Dimensional Mott System BaCo1-xNixS2-δ by the X-Ray Rietveld Method

Structural parameters of BaCo 1- x Ni x S 2 (0 ≤ x ≤1) with quasi two-dimensional electrons have been determined by the X-ray Rietveld method. This sulfide exhibits the Mott transition with varying x . The interatomic distance between Co/Ni and S(1) at the apex site of a Co 1- x Ni x S 5 square-pyramid increases with x , which is consistent with the electronic configuration (3 d 3 z 2 - r 2 ) 1+ x of Co/Ni ions. The structural data of BaCo 0.9 Ni 0.1 S 1.85 show that the sulfur vacancies are within (Co/Ni)S planes.