Evolution structurale de quelques solutions solides oxyfluorées de structure pyrochlore

Pyrochlore solid solutions Cd₂Nb_2−2xM^IV_2xO_7−2xF_2x are studied with M = Ge and Sn; the domain of existence is 0 ? x ? 0.5. We can observe two cubic domains for different values of the position parameter u. With M = Zr we obtain a pyrochlore solid solution varying between 0 ? x ? 0.875. It offers a rhomboedric distortion for 0.25 < x < 0.55 due to an ordered distribution of Nb and Zr in the (111) plans of the cell.