Lattice dynamics of Eu1-xYxMnO3 (0 ≤ x ≤ 0.5) studied by Raman and infrared spectroscopy

A systematic and detailed study of Raman and infrared active lattice excitations in the orthorhombic multiferroic manganite Eu1-xYxMnO3 (0 a parts per thousand currency sign x a parts per thousand currency sign 0.5) was carried out at room temperature. For the infrared active phonon modes the eigenfrequencies, damping constants and oscillator strengths were analyzed by Fourier-Transform Infrared Spectroscopy in the far infrared frequency range. For the Raman active phonons the same analysis for eigenfrequencies and damping constants was carried out using Raman spectroscopy in the range from 200 cm(-1) to 700 cm(-1). Y doping leads to mode-dependent phonon frequency shifts up to 8%. These are interpreted in terms of the interplay between the decrease of the reduced ion masses and the axis-dependent change of bond lengths. The latter leads to a bond softening along the a-axis and a strengthening along the c-axis, for which the highest phonon frequency increase is observed. The application of both Raman and Infrared Spectroscopy gives us sensitivity not only to symmetry properties via the selection rules but also to the involvement of different ion types within the unit cell. It is clearly shown that the disorder induced effects are of minor impact on the lattice properties and solely detected on the rare earth sites. The MnO6 octahedra remain unaffected and show the same behavior as in the stochiometric RMnO3 making Eu1-xYxMnO3 an excellent model system for a quasi-continuous fine-tuning of the lattice parameters relevant for the appearance of multiferroicity.