Microstructure and electrical properties of (Na1.015−xKx)NbO3 lead-free piezoceramics

In order to obtain the morphotropic phase boundary (MPB) and good piezoelectric properties, lead-free (Na1.015−xKx)NbO3 (x = 0.32–0.35) piezoceramics were synthesized by conventional solid state sintering. The x-ray diffraction results show that the lattice parameters of the monoclinic primitive cell peak at x = 0.34. The scanning electron microscopy and energy dispersive spectroscopy reveal that the excess sodium may be an important reason for the abnormal growth of the grains larger than 20 μm. All the samples exhibit double-like hysteresis loops and it may also be attributed to the excess Na+. Although the salient microstructure was found in the studied range, the piezoelectric and ferroelectric properties changed slightly with increasing x from 0.32 to 0.35. The values of piezoelectric coefficient d 33 obtained in this study are as high as about 75 pC/N which is close to that of normally prepared (Na0.5K0.5)NbO3 ceramics with MPB structure.