Influence of Li and la content on phase structures and electrical properties of K_0.5NaK_0.5NbO₃ lead-free piezoelectric ceramics

Lead-free piezoceramics (K_0.5NaK_0.5) _1-2xLi_xLa_xNbO₃ (where x = 0.050, 0.055, 0.060, and 0.065) have been fabricated by a conventional sintering technique. The effect of Li and La doping on the phase structure and electrical properties of (K_0.5NaK_0.5)_1-2xLi _xLa_xNbO₃ ceramics was investigated. X-ray diffraction analysis showed that the ceramics possess a perovskite structure with orthorhombic symmetry. A small amount of second phase (K₆Li ₄Nb₁0O₃₀, ∼3%) was present in KNLLN ceramics. Ferroelectric-paraelectric phase transition temperature decreases with increase in doping content. La-doping in the ceramics displayed a relative lower loss tangent (tand) from room temperature up to 350 °C. Detailed studies of dielectric and electrical properties indicate that the Curie temperature shifted to lower temperature with the increase in Li and La doping. Moreover, the dielectric maxima dropped down rapidly and the dielectric peaks became extremely broad. The weak dielectric properties for the samples of x = 0.065 can be ascribed to the formation of pseudo-cubic structures at high level of Li and La substitution. The AC conductivity increases with increase in temperature showing a negative temperature coefficient of resistance (NTCR) behavior. The low value of activation energy obtained for the ceramic samples could be attributedto the influence of electronic contribution to the conductivity.