Effect of Li content on the microstructure and properties of lead-free piezoelectric (K0.5Na0.5)1-xLixNbO3 ceramics prepared by SPS

Lead-free piezoelectric (K0.5Na0.5)1-xLixNbO3 (x = 0at%-20at%) ceramics were synthesized by spark plasma sintering (SPS) at low temperature and the effects of LiNbO3 addition on its crystal structure and properties were also studied. When the Li content was less than 6at%, a single proveskite phase with the similar structure of (K0.5Na0.5)NbO3 was formed; and a secondary phase with K3Li2Nb5O15 structure was observed in the 6at% ≤ x ≤ 20at% compositional range. Furthermore, LiNbO3 existed as the third phase when the Li content was higher than 8at%. The grain sizes increased from 200-500 nm to 5-8 μm when the K3Li2Nb5O15 and LiNbO3 like phases were formed. With increasing Li content, the relative density of the ceramics first decreased from 97% to 93% and then kept constant. The piezoelectric coefficient d33, dielectric constant, and planner electromechanical coupling factor exhibited a decreasing tendency with increasing Li content because of the decrease in density and the formation of the secondary phase such as K3Li2Nb5O15 and LiNbO3. The formation of dense microstructure with a single phase is necessary in improving the properties of the (K0.5Na0.5)1-xLixNbO3 ceramics.