Low temperature mixed spin state of Co3+ in LaCoO3 evidenced from   Jahn-Teller lattice distortions
  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. 
V. Gnezdilov, K.-Y. Choi, Yu. Pashkevich, P. Lemmens, S. Shiryaev, G.   Bychkov, S. Barilo, V. Fomin, and A.V. Yeremenko