Effects of (Bi0.5Li0.5)TiO3 addition on microstructures, electrical properties and thermal stability of BiFeO3-BaTiO3 piezoelectric ceramics

Herein, lead-free 0.7BiFeO3-(0.297-x)BaTiO3-x(Bi0.5Li0.5)TiO3+0.003BiGaO3 +0.01MnO2 (abbreviated as BF-BT-xBLT, 0 ≤ x ≤ 0.0096) ceramics have been prepared by conventional solid-state sintering. The phase structures, microstructures, piezoelectric, ferroelectric, dielectric, and thermal stability of these materials were investigated. The XRD analysis show that rhombohedral and tetragonal phases coexist in the phase structure of BF-BT-xBLT ceramic. As the BLT concentration rises, the grain size first increases to 8.6 μm and then decreases to 6.14 μm. The grain size decreased from 7.68 μm to 5.02 μm with the decrease of sintering temperature. The piezoelectric, ferroelectric and dielectric properties of the ceramic increase first and then decrease as BLT concentration increases. The optimal electrical properties are obtained by adding 0.0012 BLT, piezoelectric constant d33 = 152 pC/N, electromechanical coupling coefficient kp = 0.321, mechanical quality factor Qm = 58.184, remnant polarization Pr = 25.07 μC/cm2, Curie temperature Tc = 485 °C and depolarization temperature Td = 465 °C. The BLT addition concentration may modify the aforementioned BF-BT ceramic structures and properties, while the decrease of sintering temperature from 960 °C to 880 °C causes modest decreases of relative density of BF-BT-0.0072BLT ceramics from 94.73% to 93.56% and d33 from 146 pC/N to 135 pC/N. Enhanced piezoelectric properties of d33 = 135 pC/N, kp = 0.279, and Qm = 63.713 are obtained for BF-BT-0.0072BLT ceramic even at an extremely low sintering temperature of 880 °C. In addition, the d33 of BF-BT-0.0012BLT ceramic reached 392 pC/N at 352 °C by in-situ dynamic d33 testing. This indicates the piezoelectric properties of the piezoelectric ceramic in its actual operating state. The main novelty of this study is the relatively high piezoelectric properties obtained at low sintering temperature and the d33 reaching 392 pC/N at 352 °C. The findings suggest that the ceramic is a viable material for the use of lead-free piezoelectric ceramics.