Lattice dynamics and force constant calculation for the Raman and infra-red wave numbers of cubic bismuth-based pyrochlore compounds

Pyrochlore structure and spectroscopic studies of titanate ceramics. A comparative investigation on SmDyTi2O7 and YDyTi2O7 solid solutions

Considering the features in changing the structure and properties of rare earth titanates pyrochlores, the substituted Dy₂Ti₂O₇ may be very attractive for various applications. Effect of Sm and Y substitution on the structural properties of Dy₂Ti₂O₇ ceramic was established. These ceramics were prepared by solid-state reaction and characterized by X-ray diffraction and Raman spectroscopy. Both analysis show that YDyTi₂O₇ with the pyrochlore structure is obtained after heating at 1400°C, but SmDyTi₂O₇ has already formed after sintering at 1200°C. SEM images revealed that the average grain size was increased with the increase of heating temperature, and an un-homogeneous grain growth was detected. The average size was about 37nm and 135nm for the SmDyTi₂O₇ and YDyTi₂O₇ particles, respectively. Structural Rietveld refinements indicate that all prepared ceramics crystallize in cubic structure with space group of Fd3m. The refined cell parameters demonstrate an almost linear correlation with the ionic radius of Ln³⁺. The vibrational spectra revealed that the positions of bands are sensitive to the Ln³⁺-ionic radius, and the TiO bond strength decreased linearly with the increase of cubic lattice parameter. Raman spectra indicate that the wavenumber of OTiO bending mode is considerably shifted to lower region with increasing in mass of the Ln atom. This paper provides solid foundations for additional research of these solid solutions, which are very attractive for different fields as promising catalytic compounds for combustion applications or as frustrated magnetic pyrochlore ceramics.