Lead-free piezoelectric ceramics with composition of (0.97-x)Na1/2Bi1/2TiO3-0.03NaNbO3-x BaTiO3

Compositions in (Na1/2Bi1/2)TiO3 based ternary system, (0.97-x) (Na1/2Bi1/2)TiO3-0.03NaNbO(3)-xBaTiO(3) (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, T-c and T-f, 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 (k(t)) of 0.51 and piezoelectric charge constant (d(33)) of 110 x 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 T-f remains above 140degrees 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. (C) 2003 Kluwer Academic Publishers.