Microstructure and piezoelectric properties of lead-free (1-x)(Na0.5K0.5)NbO3-xCaTiO3 ceramics

The crystal structure of (1-x)(Na0.5K0.5)NbO3-xCaTiO(3) ceramics began to change from orthorhombic to tetragonal at x >= 0.03, 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 x >= 0.07. The Curie temperature decreased with increasing x and the specimen became a relaxor at x >= 0.03. 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 d(33)=241, k(p)=0.41, and epsilon(T)(3)/epsilon(o)=1316 were obtained from the 0.95NKN-0.05CT ceramics sintered at 1050 degrees C for 2 h, indicating that the 0.95NKN-0.05 ceramic is a good candidate material for lead-free piezoelectric ceramics.