  One- and multi-phonon excitations of the single crystalline LaCoO3 were
studied using Raman spectroscopy in the temperature region of 5 K - 300 K.
First-order Raman spectra show a larger number of phonon modes than allowed for
the rhombohedral structure. Additional phonon modes are interpreted in terms of
activated modes due to lattice distortions, arising from the Jahn-Teller (JT)
activity of the intermediate-spin (IS) state of Co3+ ions. In particular, the
608-cm-1 stretching-type mode shows anomalous behavior in peak energy and
scattering intensity as a function of temperature. The anomalous temperature
dependence of the second-order phonon excitations spectra is in accordance with
the Franck-Condon mechanism that is characteristic for a JT orbital order.
