Lattice dynamics of the α and β phases of LiFe5O8

The polarized Raman spectra of the inverse spinel LiFe5O8 (LFO) were studied for both B-site-ordered (alpha) and B-site-disordered (beta) phases. The symmetry of all the Raman lines was determined and an assignment to phonon modes involving specific atomic motions was done by comparison to lattice dynamics calculations. The spectra exhibit strongly resonant behavior, the enhancement of some one-phonon bands and all the two-phonon bands being probably related to the Franck-Condon mechanism of excitation and decay of the electronic d-d transition of Fe3+. The disordered beta phase, obtained by rapid quenching after postannealing at a temperature above the nominal order-disorder transition, coexists with remnants of the alpha phase.