Raman- and infrared-active phonons in YBaCuFeO5: Experiment and lattice dynamics.

The results of polarized Raman scattering, far-infrared (FIR) absorption, Kramers-Kronig analysis of FIR reflectance, and lattice-dynamical calculations of the perovskitelike compound YBaCuFeO 5 (space group P4mm) are reported. All 16 Raman- and infrared-active Γ-point phonons (6A 1 +2B 1 +8E) have been identified and assigned to definite atomic vibrations in close comparison with the structurally similar tetragonal YBa 2 Cu 3 O 6 system. The appearance of an additional strong Raman line at 576 cm -1 is discussed in terms of disorder-induced Raman scattering. The normal-mode frequencies are in reasonable agreement with the results of lattice-dynamical calculations in the framework of a shell model with parameters extracted from several metallic oxides and perovskite compounds