Pronounced site preference and mixed dinuclear dichalcogenide anions (SSe)2− in ternary lanthanum sulfide selenides - The solid solution LaS1.9-LaSe1.9

► Vegard series of mixed lanthanum sulfide selenides LaS1.9−xSex (0 < x < 1.9). ► Pronounced site ordering of chalcogen positions. ► Raman spectra evidence mixed (SSe)22− dinuclear anions.