Synthesis and characterization of ultrafine Ln2Ti2O7 (Ln = Sm, Gd, Dy, Er) pyrochlore oxides by stearic acid method

Stearic acid method (SAM) was developed to synthesize series of pyrochlore Ln(2)Ti(2)O(7) (Ln=Sm, Gd, Dy, Er) nanocrystals. The synthesis process was monitored by X-ray diffraction, Thermal-gravimetric-differential thermal analysis and Fourier Transform InfraRed methods. Comparing with traditional solid-state reaction (SSR), Ln(2)Ti(2)O(7) can be synthesized at relatively low temperature (700-800 degrees C) with shortened reaction time (2-4 h). The average particle size of Ln(2)Ti(2)O(7) was greatly reduced (ca. 40 nm) and the BET surface area was increased (ca. 12 m(2)/g) by using SAM. From the X-ray diffraction patterns, we found that Ln has an effect on the crystal structure of Ln(2)Ti(2)O(7), every lattice peak shifted to larger angle slightly with the increasing atomic number of Ln. Also, the lattice constant of Ln(2)Ti(2)O(7) was calculated by Jade.5 and found it decreased along with the decrease of ionic radius of Ln(3+). The morphology of obtained Ln(2)Ti(2)O(7) was determined by transmission electron microscopy technique. Results showed that the obtained Ln(2)Ti(2)O(7) were all square-like and the interplanar distance of Ln(2)Ti(2)O(7) (Ln=Sm, Gd, Dy, Er) according to (111) plane was 0.65, 0.64, 0.63, and 0.62 nm respectively, which was measured from High Resolution Transmission Electron Microscopy images. Possible reason for this phenomenon was presented. (C) 2009 Elsevier Inc. All rights reserved.