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°C. However, conventionally sintered ceramics suffer from poor piezoelectric coefficient (d₃₃) and low electrical resistivity (ρ_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 d₃₃ and ρ_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 d₃₃ and ρ_dc in CBN ceramics for developing high-temperature vibration sensors.