Search

Simultaneous achievement of large piezoelectric responses and broad service temperature range for power-type applications, such as sensors, actuators and transducers, is challenging due to trade-off between piezoelectric coefficient (d33) and Curie temperature (TC). In this study, manganese dioxide (MnO2) was introduced in 0.04BiYbO3-0.96Pb(Zr0.469Ti0.531)O3 (BY-PZT) matrix, and then based on this, Qm further was improved and tan δ got reduced via optimization of Zr/Ti ratios in the matrix, i.e., by intentional design of Ti nonstoichiometry for inhibiting pyrochlore phase. Results show that doping of appropriate amount of MnO2 led to significant increase in Qm of BY-PZT ceramics from 160 to 274, and tan δ decreased from 2% to 0.3%, while nonstoichiometry with certain Ti-deficiency amount could further increase Qm to 567 and reduce tan δ to 0.2%. Simultaneously, TC was still maintained at relatively high level for high-temperature applications. Ceramics with optimized composition of 0.04BiYbO3-0.96Pb(Zr0.469Ti0.531–1.5%)O3 + 1.3 mol%MnO2 sintered at 1100 °C exhibited optimal electrical properties of d33 = 252 pC·N−1, kp = 0.468, Qm = 567, tan δ = 0.2%, and TC = 389 °C. This study solves the problem of generation of pyrochlore phase during mass production of BY-PZT-based ceramics, and results pave the way for utilizing new power-type piezoelectric ceramic in high-temperature applications. [ABSTRACT FROM AUTHOR]

[(NaK)Li][(NbSb)Ta]O + 0.08 mol% MnO lead-free piezoelectric ceramics were fabricated successfully by a conventional solid-state reaction method. The effects of Ta substitution and K/Na ratio variation on the microstructure and properties of the ceramics have been systematically investigated. With the increasing of Ta substitution content, the orthorhombic-tetragonal transition temperature T presents obvious 'V' type variation while the Curie temperature T decreases monotonically. The ceramics properties were further enhanced by adjusting the Na/K ratio of the A-site. Under systematical optimization of the A-site and B-site elements, good overall electrical properties of d = 276 pC/N, k = 44.5%, ε/ ε = 1,175, tan δ = 0.027, T = 309 °C, P = 21.0 μC/cm, and E = 1.14 kV/mm were obtained for ceramics with Ta content x of 0.05 and Na/K ratio of 57/43 ( y = 0.07). [ABSTRACT FROM AUTHOR]

Some lead-free piezoelectrics cannot meet the requirement for application in extremely harsh high-temperature surroundings. In this work, an enhanced piezoelectric performance with high piezoelectric coefficient (d 33) and high Curie temperature (T c) has been achieved by replacing the Ti4+ with the Co3+ in Na 0.5 Bi 4.46 Ce 0.04 Ti 4- x Co x O y ceramics. The introduction of Co3+ decreases the B–O bond lengths, leading to the shrinkage of BO 6 octahedra and lattice volume. The electron localization degree of B–O bond and the polarity of the BO6 octahedra were improved by diminution of lattice volume concomitantly, which were indicated by the first principle calculations. Therefore, an enhanced piezoelectric coefficient of 22 pC/N and high T c of 690.2 °C have been realized in Na 0.5 Bi 4.46 Ce 0.04 Ti 4- x Co x O y ceramics with x = 0.02 mol. Our work gives a good paradigm to design superhigh temperature piezoelectric devices for practical application in extremely harsh circumstances. [ABSTRACT FROM AUTHOR]

K x Na 0.5-x Bi 4.46 Ce 0·04 Ti 4 O 15+y (x = 0, 0.04, 0.08, 0.12, 0.16, 0.20) ceramics were synthesized by solid state reaction. The microstructure and electrical properties of the solid solutions were characterized. It is found that the doping of appropriate amount of K improved the degree of lattice distortion of the material, and the characteristic parameter b/a of lattice distortion obtained the maximum value through structural refinement at x = 0.12. A defect dipole pair (K B i ″ − V o • • ) is formed by adjusting the defects of the material. The polarizability of defects is 4.88 × 10-37F·m2. The formation of defect dipole pairs that deflect towards the direction of spontaneous polarization reduces the difficulty of polarization and improves the piezoelectric properties. Finally, the optimal piezoelectric coefficient (d 33) of NBCT-xK ceramics is 23 pC/N, and the residual polarizability (2 P r) is 4.14 μC/cm2. The values of residual polarization rate (2 P r), piezoelectric coefficient (d 33) and b/a show the same trend, which will gradually decrease when their value increases to a certain extent. The dielectric loss of all samples below 200 °C are lower than 0.01, and the dielectric constant is relatively flat below 400 °C. Moreover, the Curie temperature (T c) of K x Na 0.5-x Bi 4.46 Ce 0·04 Ti 4 O 15+y based ceramics is increased to 686.0 °C, which will enable the ceramics to be used in oilfield logging, aerospace and military fields in high temperature environment. [ABSTRACT FROM AUTHOR]

• (Na 0.5 K 0.5- x Li x)NbO 3 system is designed to raise the depolarization temperature and Curie temperature by replacing K at A site with a small amount of Li. When x = 0.065, the desired depolarization temperature and piezoelectric activity are obtained: T d = 470 °C, d 33 = 205 pC/N. After optimizing the process conditions, the piezoelectric coefficient finally reaches at 265 pC/N. • The purpose of Al 2 O 3 doping is to enhance the thermal stability of KNN-based piezoelectric ceramics. the d 33 of 0.2 mol% Al 2 O 3 doping remains the relatively high value of 200 pC/N even at high temperatures (400–470 °C) with a decrement less than 10% (25–470°C). • This work opens a new perspective for enhancing the thermal stability of lead-free piezoelectric ceramics, and paves the way for the practical application of KNN-based ceramics at high temperatures. Obtaining both large piezoelectric responses and broad service temperature range of ferroelectric ceramics is a key challenge for practical applications due to the so-called piezoelectric coefficient (d 33)-Curie temperature (T C) trade-off. Here we report the strategy of employing Li substitution and Al 2 O 3 doping in order to enhance the depolarization temperature (T d) and thermal stability of (K,Na)NbO 3 (KNN)-based lead-free piezoelectric ceramics. All KNN-based ceramics are fabricated using conventional solid-state reaction techniques. Optimal comprehensive properties of d 33 = 205 pC/N, k p = 46.5%, ε 33 T / ε 0 = 998, tan δ = 0.047, T d = 470 °C are obtained with Li substitution of 6.5 mol%. Furthermore, doping 0.2 mol% Al 2 O 3 improves the thermal stability in the whole working temperature range of 25 – 470 °C with a d 33 decrement less than 10%, keeping the relatively high d 33 of 200 pC/N even at high temperature (400 – 470 °C). The Al 2 O 3 doping shows a further effect of inhibiting grain growth, which significantly reduces the grain size of ceramics. The results obtained in this work pave the way for the practical application of KNN-based ceramics at high temperature, such as aerospace sensors, oilfield logging, engine monitoring and injection nozzles in automobiles. [Display omitted] [ABSTRACT FROM AUTHOR]