Temperature-Induced Changes of the Electronic Structure of Ferroelectric LiTaO3

A ${}_{}{}^{181}{}_{}{}^{}\mathrm{Ta}$ Mössbauer study of LiTa${\mathrm{O}}_3$ in the temperature range from 4.2 to 1050 K reveals temperature-induced changes of the electronic structure. Both the electric-field-gradient tensor and the total electron density at the nucleus exhibit dramatic temperature dependences. The latter reflects a charge transfer from the neighboring O ions to the central Ta ion increasing nonlinearly with temperature, an effect that has been postulated theoretically on the basis of a nonlinear anisotropic polarizability of the O ion.