Raman spectroscopy of rare-earth orthoferrites RFeO3 ( R =La, Sm, Eu, Gd, Tb, Dy)

Abstract

We report a Raman scattering study of six rare earth orthoferrites RFeO3, with R = La, Sm, Eu, Gd, Tb, Dy. The use of extensive polarized Raman scattering of SmFeO3 and first-principles calculations enable the assignment of the observed phonon modes to vibrational symmetries and atomic displacements. The assignment of the spectra and their comparison throughout the whole series allows correlating the phonon modes with the orthorhombic structural distortions of RFeO3 perovskites. In particular, the positions of two specific Ag modes scale linearly with the two FeO6 octahedra tilt angles, allowing the distortion throughout the series. At variance with literature, we find that the two octahedra tilt angles scale differently with the vibration frequencies of their respective Ag modes. This behavior as well as the general relations between the tilt angles, the frequencies of the associated modes and the ionic radii are rationalized in a simple Landau model. The reported Raman spectra and associated phonon-mode assignment provide reference data for structural investigations of the whole series of orthoferrites.

Intrinsic structural distortion and exchange interactions in SmFexCr1−xO3 compounds

“…The orthorhombic space group Pnma, distorted from an ideal cubic perovskite in which Raman scattering is formally forbidden, is predicted to have 24 Raman-active modes (7A g + 5B 1g + 7B 2g + 5B 3g ) according to group theory, 26 however, 12 modes are present within a 100-600 cm À1 range for the orthorhombic Pnma perovskite structure for RCrO 3 systems. 27,28 The others are either too weak in intensity or have energies below the experimental cutoff.…”

Experimental and Theoretical Infrared Signatures of REMO3 (RE = La, Pr, Nd, Sm, and M = Co, Fe) Perovskites

“…have been discussed over the years [13][14][15][16][17][18][19][20] , but most of the work found in the literature focuses only on one or two specific compounds. Only two studies explore the effect of lattice distortion brought by the RE 3+ cation on the vibrational features of these systems: Sudheendra et al 21 followed the thermal evolution of the infrared signatures of RECoO 3 (RE=La, Pr, Nd) systems, while Weber et al 22 focused on the attribution of the Raman signatures of REFeO 3 (RE = La, Sm, Eu, Gd, Tb, Dy) systems. However both of these studies focus only on the role of the A 3+ cation and none of them considered that of the B 3+ cation.…”

Polarized Raman scattering on single crystals of rare earth orthochromite RCrO3 (R = La, Pr, Nd, and Sm)

“…Raman spectroscopy allows to probe the vibrational energy levels from an inelastic process of light scattering . It is a well‐known technique for probing the structural transitions and allows in some cases to investigate local structural changes.…”