• Kleppe, A. K.
• Comyn, T. P.
• Hall, David A.
• Daniel, L.
• Wang, G.

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 nanopolar 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.

Topics

• perovskite
• impedance spectroscopy
• grain
• grain size
• phase
• x-ray diffraction
• texture
• sintering