Berlin 2012 – wissenschaftliches Programm

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MM: Fachverband Metall- und Materialphysik

MM 51: Computational Materials Modelling VII - Oxides

MM 51.4: Vortrag

Donnerstag, 29. März 2012, 12:30–12:45, TC 006

Interplay between defect dipoles and ferroelectric polarization in a lead-free piezoelectric material — •Sabine Körbel and Christian Elsässer — Fraunhofer-Institut für Werkstoffmechanik IWM, Wöhlerstraße 11, 79108 Freiburg, Germany

KNbO₃ is a ferroelectric perovskite-type compound and a special case of the solid-solution system (K,Na)NbO₃ (KNN), which is regarded as a prospective lead-free substitute for today’s best material Pb(Zr,Ti)O₃ (PZT) in piezoelectric components. The piezoelectric properties of PZT and KNN are commonly optimized by doping. Depending on the application, ferroelectric hardness or large strain is desirable. Defect dipoles consisting of aliovalent dopants and associated oxygen vacancies can impede domain wall motion and lead to ferroelectric hardening, and in aged ferroelectrics defect dipoles can cause extraordinarily large strains [1]. Combining density-functional theory and classical empirical interatomic potentials, like in [2], we studied defect dipoles consisting of Cu substitutionals and oxygen vacancies in KNbO₃. In this way we obtained the energy needed for rotating the ferroelectric polarization around a defect dipole. This energy determines to which extent defect dipoles can pin domain walls, hence contribute to ferroelectric hardening and aging.

[1] X. Ren, Nature Materials 3, 91 - 94 (2004).

[2] S. Körbel and C. Elsässer, Phys. Rev. B 84, 014109.