- © The Mineralogical Society Of America
In this chapter, the crystal structures of sulfides and related chalcogenide compounds (involving Se, Te, As and Sb as well as S) are reviewed with emphasis on mineral phases but with some discussion of related synthetic compounds. Before presenting a systematic account of the principal families, relevant crystal chemical concepts are discussed, and structural classification schemes for these phases are reviewed.
Crystal chemical concepts
Chalcogens differ from oxygen by their moderate electronegativity. The Pauling electronegativity of oxygen is 3.44, whereas that of S is 2.58, Se 2.55, and Te 2.1 (Emsley 1994). The Shannon crystal radius of O2− is 1.40 Å, that of S2− 1.70 Å, Se2− 1.84 Å, and Te2− 2.07 Å (Shannon 1981). We have estimated the radius of As3− as about 1.78 Å, and that of Sb3− as 1.89 Å, based on the structures of selected sulfide-pnictides. The difference in polarizability of chalcogens and oxygen is of great structural importance. The electric polarizability (i.e., the value expressing the displacement of the electron cloud relative to the nucleus) is 3.88 × 10−24 cm3 for O2−, but it is 10.2 × 10−24 cm3 for S2−, 10.5 × 10−24 cm3 for Se2−, and 14.0 × 10−24 cm3 for Te2− (Pauling 1927). The polarizability values can also be interpreted as expressing covalency trends of anion-cation bonds and anion-anion interactions in the structure.
The difference between oxygen and chalcogens leads to differences in crystal chemistry of oxides and chalcogenides for nearly all element combinations, exceptions being very few. Structural features of certain chalcogenide categories are in common with hydroxides, which have low-charge and polarizable OH− groups; this is true especially for layer-like structures. There are greater similarities between the above values for S …