Sintering and electrical properties of Cu-particle-dispersed (Na,K,Li)NbO3

Cofiring of electroceramics with metals is receiving ever-increasing attention. In this paper, Cu-particle-dispersed [(Na0.5K0.5)0.94Li0.06]NbO3 (NKLN/Cu) piezoelectric composites were fabricated by protective sintering in a nitrogen gas. The X-ray diffraction (XRD) results show that only perovskite NKLN and metallic Cu phases were detected in the composites. With increasing Cu content up to 30 vol%, the relative dielectric constant ɛr markedly increased from 121 for monolithic NKLN ceramics to 3938 for NKLN–30 vol% Cu composite. The piezoelectric constant d33 decreased from 171 pC/N to undetected and electromechanical coupling factor kp decreased from 26% to undetected, showing a gradually changed profile of piezoelectric property. The decrease in piezoelectric properties with increasing Cu content was ascribed to non-piezoelectric effect of metallic phases and poling characteristics of piezoceramics/metal composites. The NKLN/Cu composites could be utilized to provide a central electrode of functionally graded microstructure (FGM) to modify conventional bimorph-type piezoelectric actuators.