Optical Study of Electronic Structure in Perovskite-Type RMO₃ (R=La, Y; M=Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu)

Abstract

Optical study of trivalent 3d transition metal oxide compounds RMO₃ with perovskite-type structure has revealed the variation of their electronic structures with the 3d element M and rare earth element R. The low energy feature is governed by electronic states in the M-O network. The charge gap, either of the Mott type or charge-transfer type, is observed for a series of RMO₃ compounds, except for metallic LaNiO₃ and LaCuO₃ compounds. The charge gap systematics has been accounted for in terms of a simple ionic model. However, the deviation from the ionic model is magnified in narrow gap compounds, where the M, 3d-O, 2p mixing appears to reshuffle the electronic states. The variation of the covalent nature of the M-O network in the RMO₃ compounds is also discussed in terms of the shell-model analysis of the phonon spectra.