Large enhancement of piezoelectric properties and resistivity in Cu/Ta co-doped Bi4Ti3O12 high-temperature piezoceramics

In this study, the electrical properties of Bi₄Ti₃O₁₂-based Aurivillius-type ceramics were tailored by a B-site co-doping strategy combining high valence Ta⁵⁺ and low valence Cu²⁺. A series of Bi₄Ti_3−x(Cu_1/3Ta_2/3)_xO₁₂ (BTCT) (x = 0, 0.005, 0.01, 0.015, 0.02, 0.025, and 0.03) ceramics were prepared by the conventional solid-state reaction method. The effect of Cu/Ta co-doping on the crystal structure, microstructure, dielectric properties, piezoelectric properties, ferroelectric properties, and electrical conductivity of these ceramics was systematically investigated. Co-doping significantly enhanced the piezoelectric properties and DC electrical resistivity of the resulting composites. The optimized comprehensive performances were obtained at x = 0.015 with a large piezoelectric coefficient (34 pC/N) and a relatively high resistivity of 9.02 × 10⁶ Ω cm at 500°C. Furthermore, the ceramic also exhibited stable thermal annealing behaviors and excellent fatigue resistance. The results of this study demonstrated great potential of the Cu/Ta co-doped Bi₄Ti₃O₁₂ ceramics for high-temperature piezoelectric device applications.     

Luminescence and electrical properties of Eu-modified Bi0.5Na0.5TiO3 multifunctional ceramics

The Eu³⁺-modified Bi_0.5Na_0.5TiO₃ (BNT) ceramics have been fabricated by the solid-state reaction method. The impact of Eu³⁺ doping on the structure, photoluminescence, and electrical properties has been studied by XRD, SEM, PL spectra, and LCR meter. X-ray diffraction analysis reveals that the crystal structure of the samples is well matched with the trigonal perovskite, and the optimal temperature of presintering is 880°C. The Eu³⁺-doped BNT ceramics show excellent red fluorescence at 614 nm corresponding to the ⁵D₀→⁷F₂ transition of Eu³⁺ under 466 nm excitation and relatively long fluorescence lifetime. The BNT-0.02Eu ceramic density is up to 5.68 g/cm³ and the relative density is up to 94.6% with sintering temperature 1075°C. The piezoelectric constant (d₃₃) of samples has been significantly improved up to 110 pC/N by Eu³⁺ doping. The BNT-0.03Eu ceramic presintered at 880°C and sintered at 1050°C has good dielectric properties and excellent luminescence properties. Eu³⁺-doped BNT ceramics make it potential applications for novel integrated electro-optical and multifunctional devices.     

Enhanced insulating and piezoelectric properties of BiFeO3-BaTiO3-Bi0.5Na0.5TiO3 ceramics with high Curie temperature

BiFeO₃-BaTiO₃ ceramics are promising lead-free piezoelectric ceramics due to their high piezoelectric properties and high Curie temperature, but their high leakage current density makes the poling difficult. In this study, a decreased leakage current density by three orders of magnitude was obtained in Bi_0.5Na_0.5TiO₃ (BNT) added 0.67BiFeO₃-0.33BaTiO₃ (BF-BT) ceramics. It was found that the largely improved insulating properties benefit from the reduced oxygen vacancies and weak reduction of Fe³⁺ to Fe²⁺ as confirmed by photoluminescence and X-ray photoelectron spectroscopy measurements, thereby contributing to high-temperature and high-field poling. In addition, the introduction of BNT leaded to increased grain size. Due to the grown grains as well as reduced oxygen vacancies and Fe²⁺, enhanced insulating and optimal piezoelectric properties with P_r = 24.2 µC/cm², d₃₃ = 183 pC/N, k_p = 0.28, and T_C = 467°C were achieved in BF-BT-0.05BNT ceramics.     

Phase,domain, and microstructures in Sr2+ substituted low-temperature sintering PZT-based relaxor ferroelectrics

The Ag-Pd internal electrode of multilayer piezoelectric ceramics needs to be sintered below 1000°C, and lead wires and components need to be welded with lead-free solder at 260°C. PNN–PMW–PZT–xSr piezoelectric ceramics with high Curie temperature (T_c > 260°C) were synthesized at a low sintering temperature (960°C) to meet the requirements of multilayer piezoelectric devices. The relationship between structures (phase, domain, and microstructures) and electrical properties (piezo/ferroelectric properties, and dielectric relaxation) in the Sr²⁺ substituted ceramics was investigated. Rietveld refinement and Raman spectra show that Sr²⁺ substitution can cause the phase change and increase the force constant of [BO₆] octahedron. The piezoelectric response increases with increasing the content of the tetragonal phase (CTP) in the rhombohedral-tetragonal (R-T) coexisted ceramics. The ceramics with 0.6 mol% Sr²⁺ substitution have minimum activation energy for domain wall movement (E_a) of 0.0362 eV which favors the formation of nanometer-sized domains, and possess excellent electrical properties (d₃₃ = 623 pC/N, d₃₃^* =783 pm/V, T_c =295°C). The higher the CTP, the lower the E_a. The lower E_a favors the rotation of polarization direction and extension, and is beneficial to the generation of the nanometer-size domains, resulting in high piezoelectric properties.     

Enhanced piezoelectric properties of Sm3+-modified PMN-PT ceramics and their application in energy harvesting

Piezoelectric materials are widely used in electromechanical energy conversion, such as in sensors, transducers, and self-powered materials. In this paper, the influence of the Sm doping content on the microstructure and ferroelectric, piezoelectric, dielectric, and field-induced strain properties of 0.70Pb(Mg_1/3Nb_2/3)O₃-0.30PbTiO₃ (PMN-PT) ceramics was investigated. Sm-doped PMN-PT ceramics with both high piezoelectric properties (d₃₃～1406 pC/N) and a large electromechanical coupling coefficient (k_p～0.69) were synthesized. Based on their piezoelectric effect, a maximum output voltage of 31 V was achieved under external forces. The output voltages showed satisfactory stability, repeatability, and sensitivity under periodic external forces; hence, Sm-doped PMN-PT piezoelectric ceramics are potential candidates for energy conversion and signal monitoring.     

Dielectric and piezoelectric properties of (Ba0.95Ca0.05)(Ti0.88Zr0.12)O3 ceramics sintered in a protective atmosphere

(Ba_0.95Ca_0.05)(Ti_0.88Zr_0.12)O₃ (BCTZ) ceramics have been produced in a protective atmosphere of industrial N₂ gas for potential piezoelectric applications. For comparison, the ceramics were also sintered at 1200–1400 °C in air. The results revealed that the reducing atmosphere of pO₂ = 5 × 10² Pa had no substantial effect on the phase structure or the microstructure of the BCTZ ceramics. The XRD patterns suggested a tetragonal to pseudocubic phase transition at sintering temperatures above 1300 °C in both atmospheres. The nitrogen-sintered BCTZ samples had higher dielectric constants _r but lower electromechanical coupling coefficients k_p than the air-sintered samples. The piezoelectric constant d₃₃ for the BCTZ ceramics was not significantly influenced by the reducing atmosphere of pO₂ = 5 × 10² Pa. The correlation of dielectric and piezoelectric properties of the BCTZ ceramics with the sintering temperature was explained based on a competing mechanism between phase structure and microstructure.     

Properties and structures of nonstoichiometric (K,Na)NbO3‐based lead‐free ceramics

The 0.968[(K_0.48Na_0.52)]Nb_0.95+xSb_0.05O₃–0.032(Bi_0.5Na_0.5)ZrO₃ [KNN_xS–BNZ] lead‐free ceramics with nonstoichiometric niobium ion were fabricated via conventional solid‐state sintering technique and their piezoelectric, dielectric and ferroelectric properties were investigated. When x = 0.010, enhanced piezoelectric properties (d₃₃ ≈ 421 pC/N and k_p ≈ 0.47) were obtained due to the construction of rhombohendral—tetragonal phase boundary near room temperature. The KNN_xS–BNZ ceramics possesses enhanced Curie temperature (T_c) with improved piezoelectric constant. A large d₃₃ of ~421 pC/N and a high T_c ~256°C can be simultaneously induced in the ceramics with x = 0.010. Especially, good thermal stability was observed in a broad temperature range. The results indicated that our work could benefit development of KNN‐based ceramics and widen their application range.     

The dielectric properties of BaTiO3 based ceramics co-doped with Bi/Mn

BaTiO₃ based ceramics (with some additives such as ZrO₂, SnO₂, etc.) were prepared by solid state reaction. Mn²⁺ or Mn³⁺ as an acceptor substituting for Ti⁴⁺ in B site and Bi³⁺ as a donor substituting for Ba²⁺ in A site were co-doped in BaTiO₃ based ceramics. The dielectric properties of BaTiO₃ based ceramics co-doped with Bi/Mn were investigated. The results show that the dielectric properties of BaTiO₃ based ceramics co-doped with Bi/Mn are affected by the mole ratio of donor and acceptor (Bi/Mn). When the mole ratio of donor and acceptor is high, dielectric dispersion behavior was observed and the dielectric constant decrease and remnant polarization, coercive field and piezoelectric constant will varied. When Bi varied from 1.0% to 2.0 mol% (Mn = 0.8 mol%), remnant polarization from 10.35 to 2.25 μC/cm², coercive field from 4 to 2.75 kV/cm, and piezoelectric constant d₃₃ from 137 to 36 pC/N respectively.     

Modified Pb(Mg1/3Nb2/3)O3-PbZrO3–PbTiO3 ceramics with high piezoelectricity and temperature stability

There is a great demand to develop ferroelectric ceramics with both high piezoelectric coefficient and broad temperature usage range for emerging electromechanical applications. Herein, a series of Sm³⁺-doped 0.25Pb(Mg_1/3Nb_2/3)O₃-(0.75−x)PbZrO₃-xPbTiO₃ ceramics were fabricated by solid-state reaction method. The phase structure, dielectric and piezoelectric properties were investigated, where the optimum piezoelectric coefficient d₃₃ = 745 pC/N and electromechanical coupling factor k₃₃ = 0.79 were obtained at the morphotropic phase boundary composition x = 0.39, with good Curie temperature T_C of 242°C. Of particular importance is that high-temperature stability of the piezoelectric and field-induced strain was obtained over the temperature range up to 230°C for the tetragonal compositions of x = 0.40. The underlying mechanism responsible for the high piezoelectricity and temperature stability is the synergistic contribution of the MPB and local structural heterogeneity, providing a good paradigm for the design of high-performance piezoelectric materials to meet the challenge of piezoelectric applications at elevated temperature.     

Phase transition behavior and electrical properties of lead-free (1 − x)(0.98K0.5Na0.5NbO3–0.02LiTaO3)–x(0.96Bi0.5Na0.5TiO3–0.04BaTiO3) piezoelectric ceramics

Lead-free piezoelectric ceramics (1 − x)(0.98K_0.5Na_0.5NbO₃–0.02LiTaO₃)–x(0.96Bi_0.5Na_0.5TiO₃–0.04BaTiO₃) (KNN–LT–BNT–BT) with x = 0–0.10 have been synthesized by a conventional sintering technique. All samples possess pure perovskite structure, showing room temperature symmetries of orthorhombic at x < 0.02, and tetragonal at 0.05 ≤ x ≤ 0.10. A coexistence of orthorhombic and tetragonal phases in the composition range of 0.02 ≤ x < 0.05 in this system is caused by the temperature of the polymorphic phase transition (PPT) decreasing to around room temperature but not the behavior of the morphotropic phase boundary (MPB). The samples near the coexistence region exhibit improved properties, which are as follows: piezoelectric constant d₃₃ = 155 pC/N, remnant polarization P_r = 24.2 μC/cm², and coercive electric field E_c = 2 kV/mm. The results indicate that although this kind of ceramics displays good properties, further study is needed to promote the stabilities of the ceramics in order to utilize them in varying temperature environments.     

Excellent piezoelectric properties of PNN-PHT ceramics sintered at low temperature with CuO addition

Multilayer components with excellent piezoelectric performance have been developed for fulfilling the requirement of new-generation electromechanical devices and systems. Multilayering of the piezoelectric ceramic requires good sinterability preferentially at lower temperature. In this study, copper (II) oxide (CuO) was utilized as the sintering additive to increase the sinterability of 0.49Pb(Ni_1/3Nb_2/3)O₃–0.51Pb(Hf_0.3Ti_0.7)O₃ (PNN-PHT) ceramics at low temperature, and simultaneously enhance the piezoelectric and dielectric properties of the ceramics. The results demonstrated that the addition of CuO influenced the sintering behavior, grain growth, and piezoelectric properties of the PNN-PHT ceramics. A ternary high performance piezoelectric PNN-PHT ceramic sintered at 1050°C with 0.5 mol% CuO exhibited excellent properties as follows: d₃₃ = 912 pC N⁻¹ and ε_r = 6665.     

Thermally stable large strain in low-loss (Na0.2K0.8)NbO3-BaZrO3 for multilayer actuators

CuO-doped (1–x)(Na_0.2K_0.8)NbO₃-xBaZrO₃ ceramics (0.0 ≤ x ≤ 0.06) were densified at 960°C. The ceramic with x = 0 exhibited a large sprout-shaped strain vs electric-field (S-E) curve and a double polarization vs electric-field (P-E) hysteresis curve, owing to the defect polarization (P_D) developed between Cu²⁺ ions at Nb⁵⁺ sites and oxygen vacancies. The sizes of the S-E and P-E loops decreased with increasing x, owing to the decrease in the number of P_Ds. The ceramic with x = 0.04 displayed small S-E and P-E curves, indicating its small dielectric loss. It exhibited large strain (0.19% at 8.0 kV/mm) at room temperature, which was maintained at 200°C. A similar strain was observed after applying 10⁶ cycles of an electric field (3.0 kV/mm). Hence, this specimen exhibited large strain with excellent thermal and fatigue properties. Moreover, the synthesized multilayer actuator using the ceramic with x = 0.04 showed excellent vibrational properties, making it promising for applications in multilayer piezoelectric actuators.     

Phase diagram and properties of Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 polycrystalline ceramics

yPb(In_1/2Nb_1/2)O₃-(1 − x − y)Pb(Mg_1/3Nb_2/3)O₃-xPbTiO₃ (yPIN-(1 − x − y)PMN-xPT) polycrystalline ceramics with morphotropic phase boundary (MPB) compositions were synthesized using columbite precursor method. X-ray diffraction results indicated that the MPB of PIN-PMN-PT was located around PT = 0.33-0.36, confirmed by their respective dielectric, piezoelectric and electromechanical properties. The optimum properties were found for the MPB composition 0.36PIN-0.30PMN-0.34PT, with dielectric permittivity ?_r of 2970, piezoelectric coefficient d₃₃ of 450 pC/N, planar electromechanical coupling k_p of 49%, remanent polarization P_r of 31.6 μC/cm² and T_C of 245 °C. According to the results of dielectric and pyroelectric measurements, the Curie temperature T_C and rhombohedral to tetragonal phase transition temperature T_R-T were obtained, and the “flat” MPB for PIN-PMN-PT was achieved, indicating that the strongly curved MPB in PMN-PT system was improved by adding PIN component, offering the possibility to grow single crystals with high electromechanical properties and expanded temperature usage range (limited by T_R-T).     

The NbO6 octahedral distortion and phase structural transition of Eu3+‐doped K0.5Na0.5NbO3–xLiNbO3 ferroelectric ceramics

A small quantity of Eu³⁺ ions were doped in the lead‐free ferroelectric K_0.5Na_0.5NbO₃–xLiNbO₃ (KNN–xLN, 0 ≤ x ≤ 0.08) ceramics to investigate the NbO₆ octahedral distortion induced by the increasing LN content. In addition, the phase structure, ferroelectric, and photoluminescence properties of K_0.5Na_0.5NbO₃–xLiNbO₃:0.006Eu³⁺ (KNN–xLN:0.006Eu³⁺) lead‐free piezoelectric ceramics were characterized. All the X‐ray diffraction, Raman spectra, dielectric constant vs temperature measurements and the photoluminescence of Eu³⁺ ions demonstrated that the prepared ceramics undergo a polymorphic phase transition (PPT, from orthorhombic to tetragonal phase transformation) with the rising LN content, and the PPT region locates at 0.05 ≤ x ≤ 0.06. The ferroelectric properties, Raman intensity ratios and photoluminescence intensity ratios show similar variations with the increasing LN content, all with a maximum value achieved at the PPT region. We believe that the close relationship among the ferroelectric properties, Raman intensity ratios, and photoluminescence intensity ratios is caused by the NbO₆ octahedral distortion. The photoluminescence of Eu³⁺ ion was discussed basing on the crystal‐symmetry principle and Judd‐Ofelt theory.     

Microstructure and Electrical Properties of Nonstoichiometric 0.94(Na0.5Bi0.5+x)TiO3–0.06BaTiO3 Lead‐Free Ceramics

0.94(Na_0.5Bi_0.5+x)TiO₃–0.06BaTiO₃ (x = ?0.04, 0, 0.02; named NB_0.46T‐6BT, NB_0.50T‐6BT, NB_0.52T‐6BT, respectively) lead‐free piezoelectric ceramics were prepared via the solid‐state reaction method. Effects of Bi³⁺ nonstoichiometry on microstructure, dielectric, ferroelectric, and piezoelectric properties were studied. All ceramics show typical X‐ray diffraction peaks of ABO₃ perovskite structure. The lattice parameters increase with the increase in the Bi³⁺ content. The electron probe microanalysis demonstrates that the excess Bi₂O₃ in the starting composition can compensate the Bi₂O₃ loss induced during sample processing. The size and shape of grains are closely related to the Bi³⁺ content. For the unpoled NB_0.50T‐6BT and NB_0.52T‐6BT, there are two dielectric anomalies in the dielectric constant–temperature curves. The unpoled NB_0.46T‐6BT shows one dielectric anomaly accompanied by high dielectric constant and dielectric loss at low frequencies. After poling, a new dielectric anomaly appears around depolarization temperature (T_d) for all ceramics and the T_d values increase with the Bi³⁺ amount decreasing from excess to deficiency. The diffuse phase transition character was studied via the Curie–Weiss law and modified Curie–Weiss law. The activation energy values obtained via the impedance analysis are 0.69, 1.05, and 1.16 eV for NB_0.46T‐6BT, NB_0.50T‐6BT and NB_0.52T‐6BT, respectively, implying the change in oxygen vacancy concentration in the ceramics. The piezoelectric constant, polarization, and coercive field of the ceramics change with the variation in the Bi³⁺ content. The Rayleigh analysis suggests that the change in electrical properties of the ceramics with the variation in the Bi³⁺ amount is related to the effect of oxygen vacancies.     

Crystal distortion and electrical properties of Ce-doped BIT-based piezoelectric ceramics

Cerium (Ce)-modified Bi₄Ti_2.94W_0.03Ta_0.03O₁₂ (BITWT) high Curie temperature ceramics (abbreviated as BITWT-xCe) were fabricated by a conventional solid-state sintering method. All BITWT-xCe ceramics had an orthogonal phase, but the structural distortion of the Ce-doped BITWT ceramics was higher than that of BITWT ceramics, which reduced symmetry and improved piezoelectric performance. The relative density (ρ_r) of BITWT-xCe ceramics was greater than 97%. Under the same conditions, the hysteresis loop of BITWT-0.04Ce ceramics had higher saturation than that of BITWT ceramics. The piezoelectric constant (d₃₃) was enhanced, and the highest d₃₃ of 24.7 pC/N at x = 0.04 was obtained, which was 25% higher than that of BITWT ceramics (d₃₃ = 19.8 pC/N). In addition, the tentative conduction mechanism of BITWT-xCe ceramics was also discussed. Two oxidations (Ce³⁺ and Ce⁴⁺) were present in the Ce-doped BITWT ceramics.     

Phase‐Composition‐Dependent Piezoelectric and Electromechanical Strain Properties in (Bi1/2Na1/2)TiO3–Ba(Ni1/2Nb1/2)O3 Lead‐Free Ceramics

New lead‐free perovskite solid solution ceramics of (1 ? x)(Bi_1/2Na_1/2)TiO₃–xBa(Ni_1/2Nb_1/2)O₃[(1?x)BNT–xBNN,x = 0.02–0.06) were prepared and their dielectric, ferroelectric, piezoelectric, and electromechanical properties were investigated as a function of the BNN content. The X‐ray diffraction results indicated that the addition of BNN has induced a morphotropic phase transformation from rhombohedral to pseudocubic symmetry approximately at x = 0.045, accompanying an evolution of dielectric relaxor behavior as characterized by enhanced dielectric diffuseness and frequency dispersion. In the proximity of the ferroelectric rhombohedral and pseudocubic phase coexistence zone, the x = 0.045 ceramics exhibited optimal piezoelectric and electromechanical coupling properties of d₃₃~121 pC/N and k_p~0.27 owing to decreased energy barriers for polarization switching. However, further addition of BNN could cause a decrease in freezing temperatures of polar nanoregions till the coexistence of nonergodic and ergodic relaxor phases occurred near room temperature, especially for the x = 0.05 sample which has negligible negative strains and thus show the maximum electrostrain of 0.3% under an external electric field of 7 kV/mm, but almost vanished piezoelectric properties. This was attributed to the fact that the induced long‐range ferroelectric order could reversibly switch back to its original ergodic state upon removal of external electric fields.     

Structure and electrical properties of Ca2+-doped (Na0.47Bi0.47Ba0.06)TiO3 lead-free piezoelectric ceramics

The lead-free piezoelectric ceramics (Na_.47Bi_.47Ba_.06)_1-xCa_xTiO₃ (x?=?0, 0.01, 0.02, 0.03, 0.05, and 0.08, abbreviated as BNBTC/0, BNBTC/1, BNBTC/2, BNBTC/3, BNBTC/5, and BNBTC/8, respectively) were obtained using the solid-state reaction method. The structure, electric conductivity, and dielectric, ferroelectric, and piezoelectric properties of the Ca²⁺-doped (Na_.47Bi_.47Ba_.06)TiO₃ ceramics were thoroughly investigated. The ceramics sintered at 1200?°C exhibit dense microstructures, having relative densities higher than 96%. The X-ray diffraction results demonstrate that all ceramics have a pure perovskite structure. The mean grain sizes of the ceramics are related to the Ca²⁺ quantity. A small quantity of Ca²⁺ ions (x?≤?0.03) improves the piezoelectric and ferroelectric properties of the samples. The dielectric behavior of the samples is sensitive to the Ca²⁺ content and electric poling. The results demonstrate that the electrical properties of the (Na_.47Bi_.47Ba_.06)TiO₃ lead-free ceramics can be well tuned by varying the Ca²⁺ quantity.     

Phase Diagram and Properties of High TC/TR−T Pb(In1/2Nb1/2) O3–Pb(Zn1/3Nb2/3)O3–PbTiO3 Ferroelectric Ceramics

A ternary ferroelectric ceramic system, (1?x?y)Pb(In_1/2Nb_1/2)O₃–xPb(Zn_1/3Nb_2/3)O₃–yPbTiO₃ (PIN–PZN–PT, x = 0.21, 0.27, 0.36, 0.42), was prepared using a two‐step precursor method. The phase structure, dielectric, piezoelectric, and ferroelectric properties of the ternary ceramics were systematically investigated. A morphotropic phase boundary (MPB) was identified by X‐ray diffraction. The optimum piezoelectric and electromechanical properties were achieved for a composition close to MPB (0.5PIN–0.21PZN–0.29PT), where the piezoelectric coefficient d₃₃, planar electromechanical coupling factor k_p, and remnant polarization P_r are 660 pC/N,72%, and 45 μC/cm², respectively. The Curie temperature T_C and rhombohedral to tetragonal phase transition temperature T_R?T were also derived by temperature dependence of dielectric measurements. The strongly “bended” MPB in the PIN–PT system was found to be “flattened” after addition of PZN in the PIN–PT–PZN system. The results demonstrate a possibility of growing ferroelectric single crystals with high electromechanical properties and expanded range of application temperature.