The effect of substituting La for Bi atoms in Bi 4 Ti 3 O 12 is investigated from first-principles calculations using the full-potential linearized augmented plane wave (LAPW) method. A comparative study of the electronic structure and lattice-dynamics properties of Bi 4 Ti 3 O 12 and La 2 Bi 2 Ti 3 O 12 shows the role of covalent bonding in the ferroelectric instabilities. The displacement patterns displayed by unstable zone-center phonon modes and a detailed analysis of the orbital contribution to the valence band illustrate the importance of Bi (La)-O interactions for the ferroelectric behavior of the doped material.
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Acknowledgments
This work was supported by Agencia Nacional de Promoción Científica y Tecnológica and Consejo Nacional de Investigaciones Científicas y Técnicas (Argentina). R.M. thanks Fundación Josefina Pratts. M.G.S. thanks support from CIUNR.
Paper originally presented at IMF-11, Iguassu Falls, Brazil, September 5–9, 2005;