Effect of Li content on the microstructure and properties of lead-free piezoelectric (K 0.5Na 0.5) 1– xLi xNbO 3 ceramics prepared by SPS

Abstract

Lead-free piezoelectric (K 0.5Na 0.5) 1– x Li x NbO 3 ( x = 0at%-20at%) ceramics were synthesized by spark plasma sintering (SPS) at low temperature and the effects of LiNbO 3 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 (K 0.5Na 0.5)NbO 3 was formed; and a secondary phase with K 3Li 2Nb 5O 15 structure was observed in the 6at% ≤ x ≤ 20at% compositional range. Furthermore, LiNbO 3 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 K 3Li 2Nb 5O 15 and LiNbO 3 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 d 33, 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 K 3Li 2Nb 5O 15 and LiNbO 3. The formation of dense microstructure with a single phase is necessary in improving the properties of the (K 0.5Na 0.5) 1– x Li x NbO 3 ceramics.