Low-temperature phase transformation and phonon confinement in one-dimensional Ta2O5 nanorods

The thermochromic phase transformations of one-dimensional Ta2O5 nanorods have been analyzed at elevated temperatures ranging from 80 to 300 K. The nanorods, grown in a large-area high-density array, are 14-22 nm wide and approximately 500 nm long. The array contained similar to 93.5% of the orthorhombic (beta) phase and similar to 6.5% of the tetragonal (alpha) phase. Low-temperature X-ray diffraction results showed complex and polymorphic thermochromic phase transformations of the beta(001), alpha(101) and beta(103) lattice planes of the nanorods, which incorporate (i) alpha-to-alpha (alpha-alpha), ( ii) alpha-alpha-beta and (iii) alpha-beta phase transitions. In comparison with the Raman scattering of three-dimensional bulk powder and two-dimensional thin films of Ta2O5, there were concurrent Raman blue- and redshifts in the one-dimensional Ta2O5 nanorods, indicating that the molecular vibrations of the nanorods were confined owing to the reduction of size and dimension. (c) 2010 International Union of Crystallography Printed in Singapore - all rights reserved