The role of silver on the stabilization of the incommensurately modulated structure in calaverite, AuTe2

Structural investigations of several minerals belonging to the calaverite group with composition Au1–xAgxTe2 (x = 0.00, 0.02, 0.05, 0.09, 0.19, and 0.33) indicate that Ag is randomly distributed on the Au sites. This suppresses the valence fluctuation of Au and, therefore, the structure modulations. The results are compared with the previously published incommensurately modulated structure of calaverite, Au0.9Ag0.1Te2, which is characterized by valence fluctuations of Au reinforced by an ordered distribution of Ag. The (3+1)-dimensional calaverite structure type is able to reproduce both (3+1)D and 3D related structures with the general formula AB2 (A = Au, Ag, Cu, Nb, Ta; B = Te). Keywords: Calaverite, modulated structure, valence fluctuations, krennerite