Dresden 2017 – wissenschaftliches Programm

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DF: Fachverband Dielektrische Festkörper

DF 2: Various Topics I

DF 2.1: Vortrag

Montag, 20. März 2017, 09:30–09:50, GER 37

Octahedral tilt nanostructure in bismuth-based relaxors — •Wolfgang Donner¹, Florian Pforr¹, Marton Major¹, Uwe Stuhr², and Bertrand Roessli² — ¹Technische Universität Darmstadt, Germany — ²Paul Scherrer Institut, Switzerland

Among the lead-free ferroelectrics, (1-x)Na_1/2Bi_1/2TiO₃-x BaTiO₃ is one of the most promising material systems. The dielectric properties around the morphotropic phase boundary at x = 0.06 are comparable to those of commonly used lead-containing ferroelectrics. However, the atomistic mechanisms leading to the relaxor properties are still unclear.

We performed a diffuse neutron scattering study in order to reveal the nanostructure of the octahedral tilt disorder of the oxygen anions. Our results show the coexistence of multiple tilt systems over a wide temperature range and a strong temperature dependence of the respective domain sizes. On this basis, we propose a model of the nanostructure featuring chemically pinned tetragonal platelets in a rhombohedral matrix. The different tilt domains are separated by a cubic intermediate phase. Furthermore, a strong temperature dependence of the planar defect density was found, which peaks at the depolarization temperature. These features react strongly to the application of an external electric field and their temperature dependence is clearly correlated with the dielectric permittivity.