Microstructures and electrical properties of lead-based PBZNZT and lead-free BNKT piezoelectric ceramics using microwave sintering

This paper is a comparative study involving sintering conditions (different sintering temperatures and time), process (conventional and microwave sintering), microstructures, and electrical measurements to investigate the mechanism of microwave absorption, and the difference in the microstructural characteristics and electrical properties of lead-based and lead-free ceramics. The lead-based piezoelectric ceramics are x(0.94PbZn1/3Nb2/3O3 + 0.06BaTiO3) + (1 − x)PbZryTi1−yO3 where x = 0.5, y = 0.52 (abbreviated as PBZNZT) and the lead-free ceramics are (Bi0.5(Na1−xKx)0.5)TiO3 where x = 0.18 (abbreviated as BNKT), all sintered by microwave heating. Experimental results indicate that PBZNZT and BNKT specimens have different microwave absorption efficiencies. Compared with BNKT samples, PBZNZT samples absorb microwave radiation more efficiently in MWS process. This might be attributed to the contribution of the dielectric constant and dipole loss which might dominate the absorption of microwave energy for ferroelectric and piezoelectric materials. HRTEM and energy dispersive spectroscopic investigations show that the grain boundaries of MWS samples exhibit less PbO and ZnO segregation than those of CS samples form PBZNZT specimens. On the other hand, BNKT specimens exhibit no compositional segregation at the grain boundaries after the CS and MWS processes. In addition, the MWS process can achieve a more uniform composition and crystallization in PBZNZT and BNKT ceramics, thus improving the electrical properties.