Structure and ferroelectric behaviour of Na0.5Bi0.5TiO3-KNbO3 ceramics |
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Authors: | G. Wang D. A. Hall T. P. Comyn L. Daniel A. K. Kleppe |
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Affiliation: | 1. School of Materials, University of Manchester, Manchester M13 9PL, UKge.wang@postgrad.manchester.ac.uk;3. School of Materials, University of Manchester, Manchester M13 9PL, UK;4. Institute for Materials Research, University of Leeds, Leads LS2 9JT, UK;5. GeePs (CNRS UMR8507, CentraleSupelec, UPMC, Univ Paris-Sud), 91192 Gif Sur Yvette Cedex, France;6. Diamond Light Source Ltd, Diamond House, Harwell Science and Innovation Campus, Didcot, Oxfordshire OX11 0DE, UK |
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Abstract: | Lead-free piezoelectric ceramics, (1?x)Na0.5Bi0.5TiO3-xKNbO3 (NBT-xKN), with x?=?0.02–0.08 were fabricated by solid-state reaction and sintering. The crystal structures and dielectric properties were measured for different KN contents. All compositions in the unpoled, as-sintered state were found to be single-phase pseudo-cubic. However, typical ferroelectric behaviour, with well-saturated polarisation-electric field hysteresis loops, was observed for certain compositions at high electric field levels. It is shown using high-energy synchrotron X-ray diffraction that the application of the electric field induced an irreversible structural transformation from the nano-polar pseudo-cubic phase to a ferroelectric rhombohedral phase. The changes in lattice elastic strain and crystallographic texture of a poled NBT-0.02KN specimen as a function of the grain orientation, ψ, conform well to those expected for a conventional rhombohedrally distorted perovskite ferroelectric ceramic. The dielectric permittivity-temperature relationships for all compositions exhibit two transition temperatures and a frequency-dependent behaviour that is typical of a relaxor ferroelectric. The transition temperatures and grain size decrease with the increasing KN content. |
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Keywords: | Lead-free Piezoelectric ceramic Domain switching Phase transformation Ferroelectric properties Synchrotron X-ray diffraction |
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