Lead-free piezoelectric ceramics with composition of (0.97−x)Na1/2Bi1/2TiO3-0.03NaNbO3-xBaTiO3

Abstract

Compositions in (Na1/2Bi1/2)TiO3 based ternary system, (0.97 − x) (Na1/2Bi1/2)TiO3-0.03NaNbO3-xBaTiO3 (x = 0, 0.01, 0.02, 0.04, 0.05, 0.06, 0.08) are synthesized using conventional solid state reaction method. Influence of BaTiO3 on crystal structure, dielectric and piezoelectric properties are investigated. All compositions can form single perovskite phase. Powder x-ray diffraction patterns can be indexed assuming a pseudo-cubic structure. Lattice constant increases with the increase of BaTiO3 concentration. Rhombohedral distortion is observed in poled samples with BaTiO3 concentration up to 6 mol%. Temperature dependence of dielectric constant and dissipation factor measurement reveals that all compositions experience two phase transitions: from ferroelectric to antiferroelectric and from antiferroelectric to paraelectric. Both transition temperatures, Tc and Tf, are lowered due to introduction of BaTiO3. Ferroelectric to antiferroelectric phase transition has relaxor characteristics. Piezoelectric properties have relatively higher value around 1 mol% to 4 mol% BaTiO3. In ceramics with x = 0.02, thickness electromechanical coupling factor (kt) of 0.51 and piezoelectric charge constant (d33) of 110 × 10−12 C/N are obtained. Addition of small amount of BaTiO3 (x = 0.01, 0.02) improves piezoelectric properties compared to NBT-NN binary system, while Tf remains above 140°C, higher than that of NBT-BT binary system composition with similar piezoelectric properties. This is in favor of the possible application of them as lead-free piezoelectric ceramics.