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 ∼93.5% of the orthorhombic (β) phase and ∼6.5% of the tetragonal (α) phase. Low-temperature X-ray diffraction results showed complex and polymorphic thermochromic phase transformations of the β(001), α(101) and α(103) lattice planes of the nanorods, which incorporate (i) α-to-α (α–α), (ii) α–α–β and (iii) α–β 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.