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

The aim of this work is to investigate the consequences of lattice distortion on the vibrational features of rare-earth perovskites. To this end, a series of REMO3 compounds has been synthesized with different rare earths (RE = La, Pr, Nd, Sm) and different transition metals (M = Fe, Co) to evaluate their respective role on lattice distortion. Thin films of these materials have been deposited by magnetron cosputtering in the reactive mode and followed by annealing in air with the same experimental conditions. Characterizations including energy-dispersive X-ray spectroscopy, X-ray diffraction, and Fourier transform infrared spectroscopy have been completed by density functional theory periodic calculations to investigate the octahedra tilt angles and to assign the vibrational spectra. The decrease of RE radius enhances the distortion of the chains of octahedra that can be followed both through the calculated mean tilt angle and experimentally by the profile of the M–O–M bending region. The magnitude of the distortion depends on the dimension of the cuboctahedric site hosting the RE that is controlled by the M radius.