Regensburg 2010 – scientific programme

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DF: Fachverband Dielektrische Festkörper

DF 8: Electrical and mechanical properties

DF 8.5: Talk

Tuesday, March 23, 2010, 15:20–15:40, H9

Ordering in the A-site mixed perovskite Bi_0.5Na_0.5TiO₃ — •Melanie Gröting, Silke Hayn, and Karsten Albe — Technische Universität Darmstadt, Materialwissenschaft, Darmstadt, Germany

Bi_0.5Na_0.5TiO₃ (BNT) is one rare example of A-site mixed relaxor ferroelectrics. BNT-based materials show extraordinarily high strains and are thus promising environmentally friendly lead-free alternatives to the toxic standard material in piezoelectric applications Pb(Zr,Ti)O₃ (PZT). BNT has aliovalent cations on the A-site in the exact ratio 1:1. For B-site mixed perovskites ordering occurs when there are significant charge and size differences between the two cation species occupying the same crystallographic site. The question arises whether in A-site mixed perovskites ordering is also favored and how it would affect the materials’ properties. Especially the origin of the relaxor behavior in BNT is still controversially discussed.

In order to gain insights into the ordering tendency of this material and to identify the driving forces of this process we investigated different cation configurations in 40-atoms cubic perovskite supercells by different theoretical approaches, encompassing simple ionic models and electronic density functional theory calculations. We discuss the different cation configurations with respect to their total energies, relaxation behavior and electronic properties. We find that rocksalt ordering is not the low-energy configuration if local relaxations are taken into account.