Structural, FT-IR, XRD and Raman scattering of new rare-earth-titanate pyrochlore-type oxides LnEuTi(2)O(7) (Ln=Gd, Dy)

We report the synthesis and structural study of mixed oxides in LnEuTi(2)O(7) series. We are presently investigating new phases with Ln=Gd and Dy, including the pyrochlore family Re(2)Ti(2)O(7) (Re=Eu, Gd and Dy). Starting from stoichiometric mixtures of elemental oxides TiO(2), Eu(2)O(3) and Ln(2)O(3) (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 degree 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 degree C. The expected compositions GdEuTi(2)O(7) and DyEuTi(2)O(7) 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 A(2)B(2)O(7) and give information about the distribution of ions between the A and B sites. X-ray powder diffraction results showed that the resulting phases GdEuTi(2)O(7) and DyEuTi(2)O(7) 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 Ln(3+) ions (Ln(3+)=Gd(3+), Dy(3+)) occupying the Re site.