Structural constitution of the LaMo6Se8 superconductor

The ternary phase diagram La-Mo-Se shows a broad homogeneity range around t he superconducting Chevrel phase LaMo6Se8. A series of single-phase samples of general formula "LaMo(6+x)Se(8-x)" (0 < x < 0.75), located inside the d omain of homogeneity of the superconducting Chevrel phase LaMo6Se8, has bee n synthesized at 1200 degrees C and characterized through X-ray, ac-magneti c susceptibility and density measurements. It has been found that the incre asing contribution of molybdenum (x) in the series does not affect much the critical temperature (T-c) of the matrix, which remains pratically constan t and close to 10 K. The same is true as far as samples' densities are conc erned. Based on crystallographical considerations, several models of differ ent distribution of the excess molybdenum (x) have been analytically determ ined. The resulting densities (d calc), when compared to the experimental v alues (d exp), served as a basis to evaluate distribution of molybdenum in real samples. The final result, supported by the X-ray powder patterns simu lation, indicates on mixed occupation of the Se sublattice consisting of(X- x) Se and the excess molybdenum (x).