Acceptor doping and actuation mechanisms in Sr-doped BiFeO3BaTiO3 ceramics

Exceptional electrostrain with minimal hysteresis and superior temperature stability under low electric field in KNN-based lead-free piezoceramics

“…S6 in the ESM), but the domains are completely switched under ±15 V. This indicates that an extra electric field with a fixed orientation exists in the system, promoting polarization in the same direction and vice versa. It has been demonstrated that defect dipoles generate an internal bias electric field (E i ) after poling, which is parallel to the poling direction and leads to similar results [14,20,40]. Therefore, the special phenomena mentioned above indicate the presence of a considerable number of defect dipoles in the system.…”

“…Considering the symmetry-conforming property of point defects, the reorientation of defect dipoles is more efficient when their orientation aligns with the matrix spontaneous polarization, as demonstrated by Geng et al [14] through DFT calculation. The orientation of the and defect dipoles matches the spontaneous polarization of the O and T phases, respectively.…”

“…The asymmetric S-E curves observed in the ceramics can be attributed to the presence of defect dipoles [14,20]. Hightemperature sintering conditions led to the formation of A-site vacancies and defects due to the volatilization of alkali metals, including Li, Na, and K. Simultaneously, Hf 4+ and Zr 4+ substituted for Nb 5+ , generating B-site vacancies and defects [34].…”

“…Due to the stable orientation of E i , lattice stretching and an increase in strain occur when the direction of the negative electric field aligns with E i . Conversely, a positive electric field causes lattice contraction and a decrease in strain [12,14].…”

“…However, the hazardous nature of lead-based ceramics has prompted the development of lead-free alternatives, even though they offer excellent overall performance [7−9]. Over the years, four main categories of leadfree piezoelectric ceramics have been developed, including materials based on BaTiO 3 (BT) [10], (Bi 0.5 Na 0.5 )TiO 3 (BNT) [11,12], (K 0.5 Na 0.5 )NbO 3 (KNN) [13,14] and BiFeO 3 (BF) [10−17]. These lead-free alternatives aim to maintain the exceptional functionality of lead-based ceramics while eliminating their environmental and health risks.…”