Laser sintering effects on the physical properties and structure of 0.94(K0.5Na0.5)NbO3-0.06LiTaO3 lead-free piezoelectric ceramics

Taking laser as the heat source for ceramic sintering, 0.94K0.5Na0.5NbO3-0.06LiTaO3 ceramics with unique physical properties were prepared. Fine ferroelectric properties with remnant polarization of 18 μC/cm2 and coercive field of 18.8 kV/cm were obtained. The piezoelectric properties and density of the ceramics were d33∼120 pC/N, kp∼36.6%, TC∼420 °C, and ρ∼4.125 g/cm3. The shift of the two phase transition temperatures (tetragonal-orthorhombic phase transition temperature TO-T shifting to 100 °C from 190 °C while Curie temperature Tc shifting to 420 from 394 °C) in laser-sintered ceramics reflects large structure distortion of phase transition and Li+ substitution of high temperature phase. Orientation degree of the texture structure based on anisometric grains of submicron diameter in the ceramics was 23%. The texture structure corresponding to the fine ferroelectric properties was resulted from the mass transform in liquid phase and strictly heating directivity of laser irradiation. O2 discharge through coaxial nozzle takes some actions like O2 annealing and effectively suppression on the volatilization of Na2O during laser sintering. Lager substitution of Li+ leads to the presence of small amount of K3Li2Nb5O15 phase damaging in d33. By analysis of the sintering effects on the properties and structure evolution, laser sintering was shown as a promising method in preparation of functional ceramics with excellent and applicable physical properties, compared to a traditional furnace sintering method.