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

Abstract

The crystal structure of (1−x)(Na0.5K0.5)NbO3-xCaTiO3 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 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.