Dielectric, piezoelectric, and vibration properties of the LiF-doped (Ba_0.95Ca_0.05)(Ti_0.93Sn_0.07)O₃ lead-free piezoceramic sheets

By the conventional solid state reaction method, a small amount of lithium fluoride (LiF) was used as the sintering promoter to improve the sintering and piezoelectric characteristics of (Ba_0.95Ca_0.05)(Ti_0.93Sn_0.07)O₃ (BCTS) lead-free piezoceramic sheets. Using X-ray diffraction (XRD) and a scanning electron microscope (SEM), the inferences of the crystalline and surface microstructures were obtained and analyzed. Then, the impedance analyzer and d33-meter were used to measure the dielectric and piezoelectric characteristics. In this study, the optimum sintering temperature of the BCTS sheets decreased from 1450 °C to 1390 °C due to LiF doping. For the 0.07 wt % LiF-doped BCTS sheets sintered at 1390 °C, the piezoelectric constant (d₃₃) is 413 pC/N, the electric-mechanical coupling coefficient (k_p) is 47.5%, the dielectric loss (tan δ) is 3.9%, and the dielectric constant (ε_r) is 8100, which are all close to or even better than that of the pure undoped BCTS ceramics. The Curie temperature also improved, from 85 °C for pure BCTS to 140 °C for BCTS-0.07 LiF sheets. Furthermore, by using the vibration system and fixing 1.5 g tip mass at the end of the sheets, as the vibration frequency is 20 Hz, the proposed piezoelectric ceramic sheets also reveal a good energy harvesting performance at the maximum output peak voltage of 4.6 V, which is large enough and can be applied in modern low-power electronic products.