A simple Bi3+ self-doping strategy constructing pseudo-tetragonal phase boundary to enhance electrical properties in CaBi2Nb2O9 high-temperature piezoceramics

Calcium bismuth niobate (CaBi₂Nb₂O₉, CBN)-based ceramics are promising candidates for high temperature application, the electrical properties of which are commonly enhanced by complex ion substitution or texture processes. Here, we report that high piezoelectricity and high resistivity were achieved in Ca_1-xBi_2+xNb₂O₉ by constructing pseudo-tetragonal boundary through a simple strategy of Bi³⁺ self-doping. At the pseudo-tetragonal boundary, Ca_0.96Bi_2.04Nb₂O₉ ceramics maintain high Curie temperature T_c = 942 °C, and show high piezoelectric coefficient d₃₃ = 15.1 pC/N and high resistivity ρ_dc = 2 × 10⁶ Ω cm (@600 °C). It is proved that the good piezoelectric property mainly originates from the increase of domain density. In addition, Ca_0.96Bi_2.04Nb₂O₉ ceramics reveal good thermal depoling performance, remaining 90% of piezoelectricity after thermal depoling at 900 ℃, which is due to small thermal expansion and structural distortion. Our work provides a promising candidate for high temperature applications and an easy way to improve the performance of Aurivillius-type piezoelectric ceramics.     

Enhanced piezoelectric and ferroelectric properties of BiFeO3-BaTiO3 lead-free ceramics by optimizing the sintering temperature and dwell time

0.7BiFeO₃-0.3BaTiO₃ (BFO-0.3BT) ceramics were prepared to uncover the impacts of sintering temperature (T_S) and dwell time (t_d) on the microstructure and electrical properties. With increasing the T_S or t_d, the grain sizes increase along with the porosity decreases, which is in favor of the alignment of dipole. However, excess T_S or t_d are inclined to cause the volatilization of Bi₂O₃, which deteriorates piezoelectric properties. Because of the R-T two-phase coexistence, low defect ions concentration and porosity, as well as appropriate grain size, the excellent d₃₃?=?208?pC/N and k_p?=?35.46% as well as P_r?=?28.52?μC/cm² were achieved in BFO-0.3BT ceramics at T_S?=?1000?°C and t_d?=?6?h. In addition,large unipolar strain 0.13% and d₃₃*?=?256.2?pm/V also were obtained in BFO-0.3BT ceramics at T_S?=?1000?°C and t_d?=?6?h. This research indicates that the porosity and defect ion concentration as well as grain size also play an important role in piezoelectric properties in BFO-BT ceramics.     

Comparison of electric field-dependent property in BaTiO3-based piezoceramics between single and coexisting phases

The evolution of electrical properties with an electric field (E) was compared between single-phase BT ceramic and phase-coexistence BT-based (BTS–0.15BCT) ceramic. The dielectric, ferroelectric, piezoelectric, and strain properties are all found to be electric field-dependent, especially for BTS–0.15BCT ceramic with small domains and easy polarization rotation induced by phase coexistence. High ferroelectric and strain properties are obtained in this ceramic because sufficient domain switching can easily be achieved. The high dielectric constant can be further elevated after poling this ceramic due to the E-induced multiphase transitions. Dynamic piezoelectric measurement reveals that the dynamic piezoelectricity can reach to ∼740 pC/N, which is much higher than the static value (∼620 pC/N) of poled BTS–0.15BCT ceramic. However, the converse piezoelectric coefficient will decrease at high E, because of the quick decrease in dynamic dielectric response caused by clamped polarization at high E. All the results demonstrate that phase-coexistence BT-based ceramic shows electric field-related properties due to the soft structure, whereas it cannot be observed in BT ceramic with stable phase structure and large domains. This work reveals the evolution difference and structure origin of electrical properties in BT-based piezoceramics with different phase structures.