Item

Abstract

As an extension of our previous study on the electron polarons
and excitons in KNbO3 and KTaO3 [1, 2], we present here results
of semi-empirical intermediate-neglect-of-differential-overlap
(INDO) calculations for free electron polarons, single-triplet
excitons and the excitonic phase in BaTiO3 perovskite crystal.
Our INDO calculations confirm the existence of self-trapped
electrons in BaTiO3. The corresponding lattice relaxation
energy is 0.24 eV and the optical absorption energy 0.69 eV. An
electron in the ground state occupies the t(2g) orbital of the
Ti3+ ion. Its orbital degeneracy is lifted by a combination of
the breathing and Jahn-Teller modes when four nearest
equatorial 0 atoms are displaced by 1.53% a(0) outwards in the
x-y plane and another two nearest oxygens shift 1.1% inwards,
along the z-axis. Our INDO calculations show that creation of
charge-transfer vibronic exciton (CTVE) in BaTiO3 Crystal is
accompanied by a strong lattice distortion; the relevant energy
gain due to CTVE formation is 2.2 eV. Moreover, our INDO
calculations predict the existence of a new crystalline phase-
that of CTVEs in BaTiO3 where strongly correlated CTVEs are
located in each unit cell of a crystal.