Comparative neutron and X-ray diffraction analysis of anionic and cationic ordering in rare-earth zirconates (Ln = La, Nd, Tb, Yb, Y)

Abstract The influence of the cation radii ratio (γ = 1.37–1.61) and temperature of the isothermal annealing on the specific features of fluorite – pyrochlore phase transition in Ln2O3: ZrO2 = 1:2 (Ln = La, Nd, Tb, Yb, and Y) systems was investigated by means of Neutron (NPD) and X-ray (XRD) powder diffractions as well as Raman spectroscopy. It was shown that with a decrease in the radius of the Ln cation in the La → Nd → Tb → Y → Yb series, the following sequence of phase transitions is observed: the pyrochlore structure → the structure of defective fluorite → the rhombohedral δ-phase. Significant advantages of NPD over XRD are demonstrated for determining the structural features of the anion sublattice. A detailed description of the parameters of the vibrational modes in Raman spectra for samples with a pyrochlore type of ordering is given, depending on the refined structural parameters.