Effects of titanium cation substitution on piezoelectric properties of bismuth sodium lanthanum titanate system

Abstract

The Bi₀.₅Na₀.₄₈₅La₀.₀₀₅TiO₃ (BNLT) compositions were modified by substituing with cations such as Zr⁴⁺, Nb⁵⁺ and Fe³⁺ ions at Ti-sites to improve piezoelectric properties. The conventionally mixed oxide method was utilized for powder preparation. The measured densities of sintered pellets (for Zr-BNLT and Fe-BNLT) were higher than 95% of theoretical densities. The lattice constants of Zr-BNLT and Nb-BNLT pellets increased with an increase in the amount of substituents. On the contrary, with an increase in the Fe content in the BNLT system, the lattice constant of Fe-BNLT pellet decreased. It was found that the higher Fe content (2.5 at%) in the BNLT system caused large grain size (up to 4.23 micron). Moreover an increase in the Fe content favored low phase transition temperature detected by DSC technique. The remanent polarizations of Zr-BNLT and Fe-BNLT pellets decreased with an increase in the amount of substituents. The remanent polarization of Zr-BNLT, Nb-BNLT and Fe-BNLT were 1.9, 20 and 7.9 μc/cm², respectively. Due to high electrical conductivity of the Zr-modified BNLT system, the optimum poling condition could not be achieved. The modified-BNLT with an addition of 1.0 at% Fe provided a piezoelectric coefficient (d₃₃) of 155 pC/N and the planar (k[subscript p]) and thickness (k[subscript t]) electromechanical coupling factor of 16.6% and 46%, respectively.