Order–Disorder Structural Transformations in Nanocrystalline Highly Imperfect Gd₂MO₅ (M = Zr and Hf) Fluorite Derivatives

Order–disorder phenomena in nanocrystalline Gd₂ZrO₅ and Gd₂HfO₅ with highly imperfect fluorite- derived structures in the range 1000–1600°C have been studied using monochromatic synchrotron X-ray diffraction and Raman spectroscopy. The results demonstrate that the synthesis process leads to the formation of two coherent phases identical in composition: a nanocrystalline disordered fluorite-like (F) phase (Fm3m) and a nanoparticulate ordered fluorite derivative (C₁) (Ia3). Their lattice parameters have been determined. In the range 1000–1600°C, the Raman spectra of the Gd₂ZrO₅ and Gd₂HfO₅ materials contain broad bands in low- and high-frequency regions, at ~118 (108), 362 (353), and 670 (665) cm^–1, which characterize the C₁ and F phases, respectively.