Dependence of crystal symmetry, electrical conduction property and electronic structure of LnFeO3 (Ln: La, Pr, Nd, Sm) on kinds of Ln3+

Abstract

Dependence of crystal symmetry, electrical conductivity, chemical state of Fe and optical property of LnFeO3 (Ln: La, Pr, Nd, Sm) on kinds of Ln3+ was investigated. All the LnFeO3 showed orthorhombic structure, with which order of high crystal symmetry was LaFeO3 > PrFeO3 > NdFeO3 > SmFeO3. Using tolerance factor, the order was successfully explained. The electrical conductivity of all the specimens could be explained by using small polaron hopping model. With increasing crystallite symmetry, electrical conductivity increased and activation energy for hopping conduction decreased. This can be ascribed to larger overlapping of Fe3d orbital and O2p orbital on nearly linear Fe-O-Fe bond in LnFeO3 with higher crystal symmetry. The larger overlapping of Fe3d orbital and O2p orbital in LnFeO3 with higher crystal symmetry can also be an origin of larger spin-spin interaction detected by Mössbauer spectroscopy and larger optical band gap observed by diffuse reflectance spectroscopy. Since chemical state of Fe, evaluated by Mössbauer spectroscopy, in LnFeO3 is fundamentally constant at +3 regardless of kinds of Ln3+, carrier concentration of LnFeO3 was revealed to be constant. It is concluded that the predominant factor which determine the electrical property of LnFeO3 is mobility affected by crystal symmetry.