ABSTRACT
c/a tetragonal compression for the title compounds having A= Zn, Cd, Hg; B=A1, Ga, In; X=S, Se, Te were discussed. A connection between c/a and the differences between tetrahedral radii for A and B species is evident, because c/a decreases as the difference increases.
Distortion of anionic tetrahedra is relevant, in particular along the parallel edges of the base diagonal and along the direction of the c axis. These are small distortions for the tetrahedra around A, but big for those around B1 at 0,1/2,1/4 and intermediate for B2 situated at 1/2,1/2,0. They indicate a prominent role of the effective charge of atoms with the higher oxidation number on the creation of the compression force. Instead the opposite happens with chalcopyrites ABX2. The effect of the anionic lone pair is notable both when rendering the so called vacant site incompressible and in conditioning the width of the angles around X atoms.
