Collect. Czech. Chem. Commun. 2007, 72, 171-184

Raman Spectroscopy of Nanocrystalline Li-Ti-O Spinels and Comparative DFT Calculations on TiyOz and LixTiyOz Clusters

Jakub Jirkovskýa, Kateřina Macounováa, Hartmut Dietzb, Waldfried Pliethb, Petr Krtila,* and Stanislav Záliša,*

a J. Heyrovský Institute of Physical Chemistry, Academy of Sciences of the Czech Republic, v.v.i., Dolejškova 3, CZ-18223 Prague 8, Czech Republic
b Department of Physical Chemistry and Electrochemistry, Dresden University of Technology, Bergstraße 66b, DE-01062 Dresden, Germany


Raman spectra of cubic nanocrystalline insertion hosts in Li-Ti-O system were measured for Li1.1Ti1.9O4-δ spinels and the corresponding delithiated titanium dioxide material. To interpret the measured data optimized geometries of cubic TiyOz and LixTiyOz were calculated using the DFT cluster approach for clusters containing up to 23 atoms. The calculated geometries were used to predict the density-of-states (DOS) diagrams and vibrational spectra of the corresponding structures upon harmonic approximation. While the DFT approach reproduces satisfactorily the main structural characteristics of TiyOz clusters, the agreement in the case of LixTiyOz clusters between calculated and real structures is less satisfactory due to the small cluster size. The band gap energies obtained from DOS diagrams represent overestimates of the actual experimental band gap energies measured on cubic Li-Ti-O oxides. The agreement between calculated and measured band gap energy improves with increasing cluster size. Raman spectra calculated under harmonic approximation from the optimized geometries reproduce all important features of the experimental Raman spectra. The agreement of DFT-calculated and experimental Raman spectra improves with increasing size of the cluster.

Keywords: Li-Ti-O spinels; Nanostructures; Raman spectroscopy; DFT calculations; Vibration analysis; Titanium oxides; Ti clusters.

References: 31 live references.