Thermal Evolution of Dielectric and Piezoelectric properties of Lead-Free Submicron-Structured (Bi0.5Na0.5)0.94Ba0.06TiO3 Ceramics

Abstract

The challenge to develop high piezoelectric sensitivity and lead-free compositions ferroelectric ceramics has bring new interest to the study of some classical ferroelectrics as (Bi0.5Na0.5)TiO3 and its solid solutions. The composition near the MPB of the system (1-x) (Bi0.5Na0.5)TiO3-xBaTiO3 with x=0.06 (BNBT6) was found to have interesting properties as lead-free piezoelectric ceramic. Processing of ceramics from nanopowders allows getting fine grained, submicron structured, ceramics that are of interest both for the basic studies of size-effects in ferroelectrics and for their use as high frequency ultrasonic transducers. Submicron-structured BNBT6 ceramics, obtained from nanometric powder synthesized by sol gel auto-combustion at 500?C, by hot-pressing at low temperature (700-800?C) and subsequent recrystallization at higher temperature, still moderate (<1100?C), in order to reduce loss of the volatile elements, have been studied. Elastic and piezoelectric coefficients, as well as electromechanical coupling factors, were determined at the resonances of, thickness poled, thin disks and shear plates. The best room temperature piezoelectric coefficient obtained in these BNBT6 fine-grained (~1&#956;m) ceramics (d33=148 pC.N-1, d31= -37 pC.N-1, d15=158 pC.N-1, kt= 40.4%, kp=26.8% and k15=40.2%) can be compared with those reported for coarse-grained ceramics prepared at higher sintering temperatures. The thermal evolution of the dielectric permittivity, piezoelectric coefficients and coupling factors has been also determined and compared with results reported for BNBT6 coarse grained ceramics, which showed a depolarization temperature of ~105?