The XRD patterns have been refined by Rietveld method. The lattice parameters determined are reported in Table , while Figures show their trend together with lattice volume as a function of x (Bi-content). The linear trend of the lattice volume reported in Figure agrees with the Vegard's law for solid solution, confirming the complete solubility of Sb/Bi in the lattice. This result could be anticipated based on the similar ionic radii between Sb 3+ and Bi 3+ ions and the same crystal structure of the two end-members.