Evidence for low octahedral-shell potential in BaTiO3 and KNbO3 from ground-state splitting of Fe3+ in cubic oxides

Measured octahedral S526-state splittings a(d) of Fe3+ paramagnetic ions in near-cubic oxides are compared, and vary in a systematic way as a function of lattice parameter 2 d. In BaTiO3 and KNbO3 a(d) is a factor 2.5 too small. This gives microscopic electronic evidence for a 30% low octahedral-shell potential V4 in these two ferroelectrics. In contrast to other ABO3 crystals these two undergo the cubic-to-rhombohedral phase-change sequence and have anisotropic overdamped soft modes. © 1976 The American Physical Society.