Structure and dielectric dispersion in cubic-like 0.5K_0.5Na_0.5NbO₃-0.5Na_1/2Bi_1/2TiO₃ ceramic

¹ Karlsruhe Institute of Technology (KIT), Institute for Applied Materials (IAM) - Hermann-von-Helmholtz-Platz 1, D-76344 Eggenstein-Leopoldshafen, Germany
² Guangxi Universities Key Laboratory of Non-Ferrous Metal Oxide Electronic Functional Materials and Devices, College of Materials Science and Engineering, Guilin University of Technology - Guilin 541004, China
³ Institute of Materials and Geoscience, Technische Universität Darmstadt - Alarich-Weiss-Straße 2, Darmstadt 64287, Germany
⁴ Forschungsneutronenquelle Heinz Maier-Leibnitz (FRM II), Technische Universität München - Lichtenbergstrasse 1, D-85747 Garching, Germany
⁵ UNSW Australia, School of Materials Science and Engineering - 2052 Sydney, Australia

^(a) ljliu2@163.com

Received: 6 January 2016
Accepted: 3 June 2016

Abstract

The nature of the cubic-like state in the lead-free piezoelectric ceramics 0.5K_0.5Na_0.5NbO₃-0.5Na_1/2Bi_1/2TiO₃ (KNN-50BNT) has been examined in detail by synchrotron x-ray diffraction (SD), selected-area electron diffraction (SAED), neutron diffraction (ND), and temperature-dependent dielectric characterization. The SD pattern of KNN-50BNT presents a pure perovskite structure with pseudocubic symmetry. However, superlattice reflections were observed by SAED and completely indexed by tetragonal symmetry with P4bm space group in ND pattern. The relaxor behavior of KNN-50BNT is compared with Pb-based and Ba-based relaxors and discussed in the framework of the Vogel-Fulcher law and the new glass model. The KNN-50BNT ceramic exhibits the strongest dielectric dispersion among them.