Crystal structure, morphology and optical behaviour of sol-gel derived pyrochlore rare earth titanates RE2Ti2O7 (RE=Dy, Sm)

Highlights: • Pyrochlore dysprosium and samarium titanates were prepared by soft sol-gel route. • XRD confirms pyrochlore single phase of Dy₂Ti₂O₇ and Sm₂Ti₂O₇ annealed at 875 °C. • TEM images show spherical shape particles with good dispersion. • Optical band gap decreases with increase in concentration of Dy or Sm precursor. Nanoscaled pyrochlore rare earth titanates RE₂Ti₂O₇ (RE = Dy, Sm) were prepared by soft-chemical sol-gel route followed by thermal treatment. Dysprosium and Samarium precursors with two compositions (0.3 and 0.5 mol) were taken separately to synthesize rare earth titanates. The size and micro-structure of prepared titanates were analyzed through X-ray diffraction (XRD), Fourier transform infra-red (FTIR) spectroscopy and Transmission electron microscopy (TEM). Pyrochlore structure of rare earth titanates (Dy₂Ti₂O₇ and Sm₂Ti₂O₇) was successfully developed as confirmed by XRD. It was found that each reflection peak corresponding to pyrochlore structure shifted slightly towards the lower angle in case of Sm₂Ti₂O₇ due to larger ionic radii of Sm³⁺ ion as compared to Dy³⁺ ion. The lattice constant of samarium titanate was found to be larger than that of dysprosium titanate. TEM images showed that the crystallites of prepared titanates with good dispersion were found to be almost spherical in shape with average size in range 33–40 nm. The optical band gap and emission wavelength were determined via UV–visible absorption and photoluminescence spectroscopy. The band gap of prepared titanates was increased on increasing the concentration of rare earth precursors (Dy/Sm), while the emission peak intensity was decreased.