Structured Diffuse Scattering as an Indicator of Inherent Cristobalite-like Displacive Flexibility in the Rare Earth Zirconate Pyrochlore LaZr1-O2-/2, 0.49<<0.51

A detailed electron and X-ray powder diffraction study has been made of the compositional and displacive flexibility of the rare earth zirconate pyrochlore (1-)ZrO2·LaO1.5=(La3+)(Zr4+)1-O2-/2,~0.5. The extent of the pyrochlore "solid solution" in specimens rapidly quenched from 1500°C is shown to be considerably narrower than previously reported and certainly less than A2 mol.% in width. A weak but highly structured and quite reproducible diffuse intensity distribution in the form of {110} *polarized sheets of diffuse intensity perpendicular to each of the six <110> real space directions is observed in electron diffraction patterns and interpreted in terms of-cristobalite-like <110> tetrahedral edge rotation of essentially rigid O(2)(La) 4tetrahedra.