Structural, optical and electronic properties of RFeO₃

Effect of R site ionic radius on the structural, optical and electronic properties of rare-earth orthoferrites (RFeO₃) (where, R = La, Pr, Nd, Sm, Eu, Tb, Dy, Y, Ho, Er, and Yb) have been investigated experimentally and theoretically. Synchrotron-based X-ray diffraction studies followed by Rietveld refinement confirmed that the lattice constants, R–O bond length and Fe–O–Fe bond angle increase systematically, whereas the Fe–O bond length (i.e. overlap between O-2p and Fe-3d orbitals) associated with FeO₆ octahedra almost remains constant throughout RFeO₃ series. The energy bandgap (E_g) of all the samples have been measured using optical absorption spectroscopy and the same is found between ~ 1.94 and 1.97 eV, i.e. E_g almost remains constant throughout RFeO₃ series. First principle DFT analysis confirmed that the “density of states” near Fermi level in all the studied samples is dominated by O-2p and Fe-3d orbitals. Thus, it appears that the constant value of Fe–O bond length (i.e. Fe-O overlap) associated with FeO₆ octahedra might be responsible for the constant value of band gap in these samples.