X-ray diffraction with synchrotron radiation has been used for comparative analysis of crystal structure evolution in Ln₂Hf₂O₇ (Ln = Sm-Dy) complex oxides with a fluorite-pyrochlore structure, synthesized by isothermal annealing of mixed hydroxides. It has been shown that heat treatment of the precursor in the temperature range 600–700°C initiates the formation of nanocrystallites with a fluorite structure. Long-range cationic ordering of the pyrochlore type appears in Ln₂Hf₂O₇ (Ln = Sm-Tb) samples once a definite crystal size has been achieved at temperatures ≥1200°C. In Dy₂Hf₂O₇ samples, a defect fluorite structure persists in the entire range of heat-treatment temperatures.

Methods of local X-ray anomalous diffraction and X-ray absorption spectroscopy based on the interaction of synchrotron radiation with condensed matter have been used to study the processes of...

The influence of Yb³⁺ cations substitution for Pr³⁺ on the structure and catalytic activity of (Pr_1−xYb_x)₂Zr₂O₇ powders synthesized via coprecipitation followed by calcination is studied using a combination of long- (s-XRD), medium- (Raman, FT-IR, and SEM-EDS) and short-range (XAFS) sensitive methods, as well as adsorption and catalytic techniques. It is established that chemical composition and calcination temperature are the two major factors that govern the phase composition, crystallographic, and local-structure parameters of these polycrystalline materials. The crystallographic and local-structure parameters of (Pr_1−xYb_x)₂Zr₂O₇ samples prepared at 1400 °C/3 h demonstrate a tight correlation with their catalytic activity towards propane cracking. The progressive replacement of Pr³⁺ with Yb³⁺ cations gives rise to an increase in the catalytic activity. A mechanism of the catalytic cracking of propane is proposed, which considers the geometrical match between the metal–oxygen (Pr–O, Yb–O, and Zr–O) bond lengths within the active sites and the size of adsorbed propane molecule to be the decisive factor governing the reaction route.

The process of Dy₂Zr₂O₇ (r_Dy3+/r_Zr4+ = 1.426) nanocrystals formation and evolution upon calcinations up to 1400 ^oC has been investigated by means of synchrotron radiation X-ray diffraction (XRD) and Raman spectroscopy. We observed that isothermal calcination of the X-ray amorphous precursor first leads to the formation of oxide nanocrystalline powders with a defect fluorite structure at 800 ^oC/3 h. The nucleation and growth of pyrochlore phase take place in nanodomains with pyrochlore-type superstructural ordering of cations and anions inside a well crystalline fluorite matrix at > 1200 ^oC. This is perhaps the first XRD study that reports the presence of a weak pyrochlore-type superstructure in the Dy₂Zr₂O₇.