We report a Raman scattering study of six rare-earth orthoferrites $R{\mathrm{FeO}}_3$, with $R$ = La, Sm, Eu, Gd, Tb, Dy. The use of extensive polarized Raman scattering of ${\mathrm{SmFeO}}_3$ 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 allow correlating the phonon modes with the orthorhombic structural distortions of $R{\mathrm{FeO}}_3$ perovskites. In particular, the positions of two specific $A{}_g$ modes scale linearly with the two ${\mathrm{FeO}}_6$ octahedra tilt angles, allowing the distortion to be tracked throughout the series. At variance with literature, we find that the two octahedra tilt angles scale differently with the vibration frequencies of their respective $A{}_g$ 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.

Correlation between spin-phonon coupling and the magnetoelectric properties of ${\text{EuMnO}}_3$ and ${\text{GdMnO}}_3$ were investigated using ceramic samples in this work. The experimental results evidence a stronger spin-phonon coupling in ${\text{GdMnO}}_3$ than in ${\text{EuMnO}}_3$, as well as a clear anomaly in the phonon contribution for the dielectric constant. This anomaly is located at the paramagnetic-incommensurate antiferromagnetic phase-transition temperature of ${\text{GdMnO}}_3$, corroborating the existence of a magnetoelectric effect in this system. The absence of the magnetoelectric effect in ${\text{EuMnO}}_3$ is due to the existing disorder revealed in this compound by the striking thermal metastability and the large decrease in the activation energy associated with the dielectric relaxation processes. This kind of behavior has no counterpart in ${\text{GdMnO}}_3$. In fact, it has been confirmed that the existence of spin-phonon coupling is not a sufficient condition for the existence of magnetoelectric property, and other mechanisms have to be considered in order to understand the magnetoelectric properties.

The superiority of Cu–Ce mixed oxides prepared by precipitation (versusimpregnation and exotemplating) was ascribed to their excellent redox properties, linked to the Ce⁴⁺/Ce³⁺and Cu²⁺/Cu⁺redox pairs.