Premium
Influence of phonon confinement, surface stress, and zirconium doping on the Raman vibrational properties of anatase TiO 2 nanoparticles
Author(s) -
Lejon Christian,
Österlund Lars
Publication year - 2011
Publication title -
journal of raman spectroscopy
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.748
H-Index - 110
eISSN - 1097-4555
pISSN - 0377-0486
DOI - 10.1002/jrs.2956
Subject(s) - anatase , raman spectroscopy , materials science , doping , phonon , annealing (glass) , analytical chemistry (journal) , condensed matter physics , chemistry , optics , composite material , biochemistry , physics , optoelectronics , chromatography , photocatalysis , catalysis
We present a comprehensive analysis of the Raman spectra of pure and zirconium‐doped anatase TiO 2 nanoparticles. To account for the wavenumber shifts of the E g (ν 6 ) mode as a function of particle size ( L ) and dopant concentration ( x ), a modification of the standard phonon confinement model (PCM) is introduced, which takes into account the contribution of surface stress by means of the Laplace–Young equation. Together with X‐ray diffraction (XRD) and transmission electron microscopy data, our analysis shows that the surface stress contribution to the observed blue shift of the Raman wavenumber is of the same magnitude as the spatial phonon confinement effect. Annealing experiments show that Zr‐doped nanoparticles exhibit retarded grain growth and delayed anatase‐to‐rutile phase transition by up to 200 K compared to pure anatase TiO 2 . XRD shows that Zr doping leads to a unit cell expansion of the anatase structure. Applying the modified PCM to the x ‐dependent variations of the E g (ν 6 ) Raman mode, the mode‐Grüneisen parameter is found to increase abruptly at x > 0.07 with a concomitant mode softening. This coincides with the x range over which the Zr cations are reported to be displaced from their position in the tetrahedral lattice, and where Zr precipitation occurs upon annealing. The results have implications for the interpretation of Raman spectra of ionic metal oxide nanoparticles and how these are modified upon cation doping. Copyright © 2011 John Wiley & Sons, Ltd.