Influence of the synthesis route on the electrical and mechanical properties of a modified 0.99 Bi0.5(Na0.8 K0.2)0.5 TiO3 − 0.01 Bi (Mg2/3Nb1/3) O3 lead-free ceramics

Abstract

The effects of the processing technique on the properties of modified 0.99 Bi_0.5(Na_0.8 K_0.2)_0.5 TiO₃ − 0.01 Bi (Mg_2/3Nb_1/3) O₃ or BNKT-BMN-based ceramics were investigated. The ceramic samples were synthesized by two different techniques, a conventional solid-state technique (CS) and a two-step technique (2-Step). Both techniques yielded pure perovskite phases without any impurity phase. The 2-Step samples presented a finer grain with a higher density than the CS technique. The 2-Step technique also enhanced many electrical properties such as the dielectric constant (ε_r), energy density (W_rec), dielectric breakdown strength (E_b), electro-strain (S), normalized strain (d₃₃*), piezoelectric coefficient (d₃₃), piezoelectric voltage constant (g₃₃), and figure of merit (FoM). Mechanical properties such as hardness (H) and elastic modulus (E) were as well improved by this technique. However, the 2-Step technique promoted a higher heterogeneous conduction, resulting in a higher degree of loss tangent (tanδ)-frequency dispersion, while the observed tanδ values were still low. Therefore, the 2-Step technique positively affects the properties of the studied ceramics and may also positively impact other lead-free Bi-based piezoelectric ceramic systems.