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Correlation between ferroelectricity and electronic density of states near the Fermi level in BaTiO 3
Author(s) -
Hidaka M.,
Tokiwa N.,
Takahashi S.,
Choi J.Y.,
Lee J. M.
Publication year - 2004
Publication title -
physica status solidi (b)
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.51
H-Index - 109
eISSN - 1521-3951
pISSN - 0370-1972
DOI - 10.1002/pssb.200301981
Subject(s) - ion , atomic orbital , fermi level , ionic bonding , density of states , valence (chemistry) , electronic structure , ferroelectricity , atomic physics , crystallography , physics , materials science , condensed matter physics , chemistry , electron , optoelectronics , quantum mechanics , dielectric
The electronic density of states in BaTiO 3 is studied by means of X‐ray absorption near‐edge structure in a vicinity of a Ti K edge and Ba L edges. A 4pπ band of the Ti ion and a 5dπ band of the Ba ion having a high‐density unoccupied state occupy a level just above the Fermi level ( E F ). The pre‐edge peaks give that, in addition to an O 2− 2p valence band, the electronic density of states below E F are composed of negative‐charge‐transfer bands 3d 1 , 3d 1 $ \underline {\rm L} $ and 3d 2 $ \underline {\rm L} $ 2 of Ti ions and 4f 1 , 4f 1 $ \underline {\rm L} $ and 4f 2 $ \underline {\rm L} $ 2 of Ba ions. The 3d 1 , 3d 1 $ \underline {\rm L} $ and 3d 2 $ \underline {\rm L} $ 2 bands of Ti ions gives that a mixture of the different oxidation states Ti 2+ and Ti 3+ is present in addition to Ti 4+ . The 4f 1 , 4f 1 $ \underline {\rm L} $ and 4f 2 $ \underline {\rm L} $ 2 bands are induced by a hybridization between Ba 2+ 4d and O 2– 2p orbitals via an electronic configuration interaction between the 4f and 4d orbitals of the Ba ion. The disappearance of the 4f 1 , 4f 1 $ \underline {\rm L} $ and 4f 2 $ \underline {\rm L} $ 2 bands in the ferroelectric phase suggests that the collective displacement of Ba ions from ideal ionic sites of the cubic perovskite‐type structure reduces the hybridization between the Ba and O ions. This gives that the effective charge on the O ions is increased and induces a large dipole moment between the O ions and the Ti ions, which are at an off‐center position of TiO 6 octahedra in the ferroelectric phase. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)