Microstructure and piezoelectric properties of lead-free (1-x) (Na _0.5K_0.5) NbO₃-xCaTiO₃ ceramics

The crystal structure of (1-x) (Na0.5 K0.5) NbO3 -x CaTiO3 ceramics began to change from orthorhombic to tetragonal at x0.03, then became a morphotropic phase boundary in which both the orthogonal and tetragonal phases coexisted at 0.03<x<0.07, and was converted to tetragonal structure at x0.07. The Curie temperature decreased with increasing x and the specimen became a relaxor at x0.03. A dense microstructure with large grains was developed at 0.04<x<0.07 due to liquid phase sintering. The relative density, grain size, and liquid phase considerably influenced the piezoelectric properties of the specimens. High piezoelectric properties of d33 =241, kp =0.41, and ε3T / εo =1316 were obtained from the 0.95NKN-0.05CT ceramics sintered at 1050 °C for 2 h, indicating that the 0.95NKN-0.05 ceramic is a good candidate material for lead-free piezoelectric ceramics.