Evolution of the phonon density of states of LaCoO ₃ over the spin state transition

The phonon spectra of LaCoO ₃ were studied by inelastic neutron scattering in the temperature range of 4-120 K. The DFT calculations of the lattice dynamics have been made for interpretation of the experimental data. The observed and calculated phonon frequencies were found to be in a reasonable agreement. The evolution of the phonon density of states over the spin state transition was analyzed. In the low-temperature range (T < 50 K), an increase in the energy of resolved breathing, stretching, and bending phonon modes was found, followed by their softening and broadening at higher temperatures due to the spin state transition and relevant orbital-phonon coupling.