Relaxor behavior and dielectric properties of (La, Ta)-modified (K0.5Na0.5)NbO3 lead-free ceramics

Lead-free relaxor ceramics with composition (Na0.5K0.5)(1-3x)LaxNb0.95Ta0.05O3 (KNTN-La-x) were prepared by the conventional solid-state route. The ferroelectric relaxor behavior and dielectric properties of KNTN-La-x ceramics were systemically investigated. X-ray diffraction analysis showed that the crystal structure of the ceramics changed from orthorhombic to pseudo-cubic with increasing La-doping level. Dielectric study revealed that KNTN-La-x ceramics underwent a transition from a normal ferroelectric to relaxor-like ferroelectric. Furthermore, P-E hysteresis loops, which were of slim-loop type with small remnant polarization values in the composition range of 0.015 <= x <= 0.03 confirmed the ferroelectric relaxor behavior of KNTN-La-x ceramics. The samples of KNTN-La-x ceramics in the composition range from x = 0 to 0.015 exhibited good electrical properties, piezoelectric constant d(33) of 98-119 pC/N and electromechanical coupling coefficients k(p) of 33.2-37.0%, respectively. The results show that the series of KNTN-Lax ceramics is one of the promising lead-free materials for electromechanical transducer applications. (C) 2009 Elsevier B.V. All rights reserved.