Structural, FT-IR, XRD and Raman scattering of new rare-earth-titanate pyrochlore-type oxides LnEuTi2O7 (Ln = Gd, Dy)

We report the synthesis and structural study of mixed oxides in LnEuTi2O7 series. We are presently investigating new phases with Ln = Gd and Dy, including the pyrochlore family Re2Ti2O7 (Re = Eu, Gd and Dy). Starting from stoichiometric mixtures of elemental oxides TiO2, Eu2O3 and Ln2O3 (Ln = Gd and Dy), single-phase samples were obtained using a conventional ceramic method. The presence of crystalline phases after heat treatment from 1000 to 1200 °C was studied by combining XRD and Raman spectroscopy. X-ray diffraction combined to the Raman analysis confirmed the powder's single-phase nature at 1200 °C. The expected compositions GdEuTi2O7 and DyEuTi2O7 were confirmed by energy dispersive spectroscopy (EDAX) and X-ray diffraction (XRD). FT-IR spectra of the obtained compounds also show the absorption bands corresponding to the pyrochlore structure A2B2O7 and give information about the distribution of ions between the A and B sites. X-ray powder diffraction results showed that the resulting phases GdEuTi2O7 and DyEuTi2O7 crystallize with the pyrochlore type structure, cubic Fd3m space group. The structures are determined by Rietveld refinement. The evolution of cell parameters and interatomic distances as a function of lanthanide cation size is discussed. The refined cell parameter a, and the positional coordinate, x, for O, determinated from Rietveld refinements, were related to the Ln3+ ions (Ln3+ = Gd3+, Dy3+) occupying the Re site.