Microwave sintering of CaBi2Nb2O9 ceramics for improved piezoelectric response and electrical resistivity

CaBi2Nb2O9 (CBN) ceramic is a promising sensing element to convert vibration to electrical signal at temperatures higher than 600 degrees C. However, conventionally sintered ceramics suffer from poor piezoelectric coefficient (d(33)) and low electrical resistivity (rho(dc)). Here, we report that CBN ceramics can be prepared by microwave sintering (MS) to mitigate volatilization issue of Bi2O3 and thus suppress the generation of oxygen vacancies usually seen in conventional sintering (CS) as demonstrated by X-ray photoelectron spectroscopy (XPS) analysis and mass-loss measurement. As compared to the CS, the MS is more favorable for reducing the sintering time, and obtaining a dense, fine, and uniform grain morphology as revealed by scanning electron microscopy (SEM) characterizations of both surface and interior of the CBN ceramics, leading to an enhancement of 86% and 75% in d(33) and rho(dc), respectively. Piezoresponse force microscopy (PFM) as combined with Rayleigh law analysis clearly revealed that the enhancement of piezoelectric properties was attributed to the thinner domains, the higher domain wall density, and the enhanced domain wall motion in the MS-940 samples. This study paves an important road to simultaneously improve both d(33) and rho(dc) in CBN ceramics for developing high-temperature vibration sensors.