Structural characteristics of pyrochlore formation

By calculating the value of the unknown oxygen positional parameter x for a large number of A3+2B4+2O7 pyrochlores, it was determined that increasing the radius of the A cation in a series of constant B increased the value of x, and that increasing the radius of the B cation in a series of constant A decreased the value of x. The region of pyrochlore formation has a range of x values from 0.404 to 0.432 and contains BO6 polyhedra that closely approach Oh symmetry and AO8 polyhedra that are highly deformed. It was shown that the characteristics of the BO6 polyhedra were the most important in determining whether or not a pyrochlore would form.