DIELECTRIC AND PIEZOELECTRIC PROPERTIES OF LEAD-FREE (Bi0.5Na0.5)0.94Ba0.06TiO3 + x%Ce2O3 + y%La2O3 + z%Y2O3 COMPOUNDS SYNTHESIZED BY SOL–GEL TECHNIQUE

Abstract

( Bi 0.5 Na 0.5)0.94 Ba 0.06 TiO 3 + x% Ce 2 O 3 + y% La 2 O 3 + z% Y 2 O 3 compounds (named BNT–BT– x/y/z) were synthesized by a sol–gel technique, for (x,y,z) = (0,0,0), (0.25, 0.25, 0.25), (0.25, 0.5, 0.5), (0.5, 0.25, 0.25) and (0.5, 0.5, 0.25). The structural variation according to the different system compositions is investigated by X-ray diffraction analyses. The results shows that the addition of Ce2O3 , La2O3 or Y2O3 in BNT–BT system, do not modify the crystalline structure, and a rhombohedral–tetragonal morphotropic phase boundary is maintained for different dopant addition. The BNT–BT–x/y/z-based ceramics sintered at relatively low temperature (1100°C) exhibit a good densification ratio. The optimum dielectric and piezoelectric properties are obtained with the BNT–BT–0.5/0.25/0.25 composition. High dielectric properties at room temperature (εr > 1000) and low dielectric losses (tan δ < 4 × 10-2) are obtained for this composition. This compound exhibits a piezoelectric constant d33 of 95 pC/N, a good polarization behavior is observed with high remanent polarization Pr of 9.21 μC/cm2 and low value coercitive field Ec of 2.66 kV/mm.