Enhanced piezoelectric performance of donor La3+-doped BiFeO3–BaTiO3 lead-free piezoceramics

Abstract Lead-free 0.70Bi1.03FeO3-0.30Ba(1-x)LaxTiO3 piezoelectric ceramics (with x = 0.000, 0.005, 0.010, 0.015 and 0.035 abbreviated as 0.0BaLa, 0.5BaLa, 1.0BaLa, 1.5BaLa and 3.5BaLa) were prepared through the conventional solid-state reaction route followed by water quenching process. The X-ray diffraction profile shows that the substitution of Ba2+ = 1.61 A with a donor ion, La3+ = 1.36 A, has a profound impact on the crystal symmetry as results the crystal structure transform from dominant rhombohedral (R) to tetragonal (T) phase. A large remnant polarization (Pr = 30.3 μC/cm2) and an enhanced direct piezoelectric coefficient, (d33 = 297 pC/N) together with a high Curie temperature (TC = 530 °C) was obtained near to the morphotropic phase boundary (MPB) of the R and T phases. A maximum strain of (Smax = 0.188%) with corresponding converse piezoelectric coefficient (d33* = 340 pm/V) and low strain hysteresis (≈20%) was found for 1.5BaLa ceramic. Additionally, the water quenching effect was more prominent for 1.0BaLa ceramic as observed from the high thermal hysteresis in heating/cooling results of the dielectric constant (er), leading to the enhancement of ferroelectric switching behavior. Hence, a small amount of La3+-substitution for Ba2+-site is more effective for the enhancement of ferroelectric and piezoelectric properties, similarly to the donor La3+-doped Pb(Zr,Ti)O3 ceramic.