Microstructural and high-temperature dielectric, piezoelectric and complex impedance spectroscopic properties of K0.5Bi0.5TiO3 modified NBT-BT lead-free ferroelectric ceramics
M. Mesrar, Abdelhalim Elbasset, N-S. Echatoui, Farid Abdi, T. Lamcharfi
Abstract
Solid solutions (1-x-y)(Na 0.5 Bi 0.5 )TiO 3 -xBaTiO 3 -y(K 0.5 Bi 0.5 )TiO 3 with (x (mol.%) = 0, 7 and 100); y(mol.%) = 0, 20 and 100) compositions have been prepared by a conventional solid-state reaction method, and their structure, dielectric properties and depolarization temperature have been examined. At room temperature, X-ray diffraction (XRD) patterns reveal that the crystalline structure of the ceramics was perovskite. The morphotropic phase boundary (MPB) of the ternary system lying between rhombohedral ( R3c ) and tetragonal ( P4mm ) phases is in the range of (x (mol.%) = 7 and y (mol.%) = 20). The Raman-active modes for 0.73NBT-0.07BT-0.20KBT were separated and identified under the framework of group theory. SEM micrographs illustrate the quasi-uniform distribution of the grains, which are compact. The dielectric properties of the ceramics were studied in the frequency range of 1 kHz–100 kHz from ambient temperature to 600 °C. Dielectric measurements indicate that all ceramics show a diffuse phase transition near the temperature (T m ) for diffusivity of the order of 1.4–1.7 and a shift of (T m ) towards high temperatures. The resistance and capacitance of the various contributors (grain and grain boundary) in our samples are also discussed using a brick-layer model. Excellent piezoelectric properties for d 33 = 146 pCN −1 and electromechanical coupling factors k p = 29.4% were observed at morphotropic phase boundary (MPB), which was assumed to be associated with the coexistence of rhombohedral and tetragonal phases and accurate grain size. This work establishes a new approach for improving lead-free piezoelectric ceramics based on 0.73NBT-0.07BT-0.20KBT.