The tolerance factors of the pyrochlore crystal structure

Abstract

The tolerance factor (t) concept, widely used in crystallochemical analysis of perovskites ABO₃, is here applied to A₂B₂O₇ fluorite-derivative superstructure: pyrochlores. Based on geometrical considerations of the different cation coordination polyhedra two tolerance factors for pyrochlores are introduced. The t values were calculated for 315 pyrochlores. A stability field is proposed to distinguish A²⁺₂B⁵⁺₂O₇ pyrochlores from A²⁺₂B⁵⁺₂O₇ weberites. A relationship between the tolerance factors and dielectric properties and their applicability to analyze structure-propoerty relations within this family of compounds is also discussed.