Lead-free 0.75BiFeO 3 –0.25BaTiO 3 (0.75BF–0.25BT) ceramics have been extensively studied because of their high Curie temperature. The aging behavior and thermal stability of piezoceramics play decisive roles in their device applications. In this work, effects of Mn doping on the phase structure, aging behavior, and thermal stability of 0.75BF–0.25BT ceramics were characterized and related mechanisms were investigated. With the increase in Mn content, the typical rhombohedral phase of 0.75BF–0.25BT ceramics changed to the coexistence of pseudo-cubic and rhombohedral phases. Mn modification enhanced the aging behavior and thermal stability of ceramics obviously. The aging rates of d 33 and k p for 0.75BF-0.25BT ceramics with 1.0 mol% Mn are 1.3% and 1.1%, respectively, which are only 1/4 those values for the undoped ceramics. The variation of ε r of 0.75BF-0.25BT ceramics with 1.0 mol% Mn is half of undoped ceramics under 500℃. The depoling temperature of 0.75BF-0.25BT ceramics with 1.0 mol% Mn was 450℃, which is about 200℃ higher than that of undoped ceramics. The enhanced aging behavior results from the decreased defect concentrations, and the better thermal stability is owing to the significantly improved poling state due to the enhanced resistivity, large grain size, and decreased crystal distortion by Mn modification. These results reflect that a proper amount of Mn doping is an effective way to enhance the aging behavior and electric thermal stability.
Ecologically sustainable hard type piezoelectric ceramics are highly demanded for high power transducer applications in replacing lead-based piezoelectric ceramics. In this study, MnO was proposed as acceptor dopant to modify the electric properties of 0.75BiFeO 3 -0.25BaTiO 3 piezoelectric ceramics. Results showed that MnO doping reduced the lattice distortion of rhombohedral phase and facilitated the formation of pseudo cubic phase of 0.75BiFeO 3 -0.25BaTiO 3 system. Moreover, it caused the diversity of domain morphology and reduced the domain size as well. XPS analysis indicated that Mn 2+ ions suppressed the transition from Fe 3+ ions to Fe 2+ ions and gave rise to the increase of oxygen vacancies . Accordingly, the introduction of MnO synergistically increases the d 33 , K p , and Q m and lowers the tan δ of 0.75BiFeO 3 -0.25BaTiO 3 ceramics. The abnormal enhancement in hard type properties is ascribed mainly to the increase of extrinsic contribution rather than the pinning effect arising from oxygen vacancies. Finally, based on an optimal 0.75Bi(Fe 0.985 Mn 0.015 )O 3 -0.25BaTiO 3 system, an atomizer prototype was fabricated. The remarkable atomization effect suggests a competitive potential of 0.75BF-0.25BT ceramic for transducer application.
0.75BiFeO 3 -0.25BaTiO 3 lead-free ceramics have been considered promising candidates for high-temperature piezoelectric applications. However, their dielectric and piezoelectric properties severely degrade with increasing temperature. In this work, improved dielectric and piezoelectric thermal stability was obtained in CuO-modified 0.75BiFeO 3 -0.25BaTiO 3 ceramics. CuO addition increases the volume fraction of the rhombohedral phase in the 0.75BiFeO 3 - 0.25BaTiO 3 ceramics and makes the chemical heterogeneity disappear. The dielectric and piezoelectric anomalies are eliminated near 300 °C and return with CuO additions, and the temperature degradations of the dielectric constant and piezoelectric coefficient of 0.75BiFeO 3 -0.25BaTiO 3 ceramics with 0.008 mol CuO in the range from 25 to 400 °C decrease by 85% and 60%, respectively. Furthermore, the depoling temperature and piezoelectric coefficient of 0.75BiFeO 3 -0.25BaTiO 3 ceramics with 0.008 mol CuO are 570 °C and 131 pC/N, respectively. These results indicate that CuO addition is an effective approach to improve both the dielectric and piezoelectric thermal stability of 0.75BiFeO 3 -0.25BaTiO 3 ceramics.
0.75BiFeO 3 -0.25BaTiO 3 (0.75BF-0.25BT) ceramics have been widely studied because of their high Curie temperature , good thermal stability and lead-free trait. The evolution of domain motion during electric poling and thermal depoling processes is closely related to the piezoelectric properties and thermal stability of ferroelectric ceramics . Herein, the non-180° domain reversals of 0.75BF-0.25BT ceramics in these two processes were investigated by an in situ XRD technique. The non-180° domain switching fraction during the poling and depoling processes was calculated quantitatively based on the (111) and (11 1 ‾ ) diffraction peaks. During the poling process, the non-180° domain reversal percentage N 111 and piezoelectric properties increase abruptly when the poling field exceeds 35 kV/cm and then saturate at the electric field of 50 kV/cm (N 111 reaches the maximum value of 59%). The domains switched under the poling electric field of 50 kV/cm are stable below 500 °C. The depoling temperature is sensitive to the domain switching fraction under different poling electric fields, and the ceramics under a strong poling field possess excellent thermal stability and high depolarization temperatures. This work revealed the relationship between the electric properties, domain switching, poling electric field, and depoling temperature in the 0.75BF-0.25BT ceramics, which may pave the way to enhancing the room temperature piezoelectric properties and their thermal stability.
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