Preparation and crystal chemistry of some rare earth vanadium (IV) pyrochlores (RE)2V2O7; RE = Lu, Yb, Tm, Lu1−xYx, Lu1−xScx

The preparation of the phases (RE)2V2O7 where RE = Lu, Yb, Tm, and the solid solutions ScxLu1−x (x = .10 → .50) and YxLu1−x (x = .20 and .40), using a COCO2 buffer system are described. Precision lattice constants were determined and compared with previous work, finding good agreement with (1) but not with (2). The solid solution (ScxLu1−x)2V2O7 exists as a pyrochlore to x = .30, compared with x = .55 for the similar (ScxLu1−x)2 Ti2O7 system. Chemical analysis on the members x = .40 and x = .50 indicate significant amounts of V(III) and X-ray data show a diminishing intensity for the “ordering” reflections (h, k, l all odd). These results suggest that Lu(III), Sc(III), V(III) and V(IV) are partially disordered over both cation sites tending toward a C-type (RE)2O3 structure or a defect fluorite structure with increasing x.