Achieving both large transduction coefficient and high Curie temperature of Bi and Fe co-doped PZT piezoelectric ceramics

Achieving both the large transduction coefficient (the product of piezoelectric charge d₃₃ and voltage coefficients g₃₃) and high Curie temperature is very important to improve the power generation performance and their thermal stability of piezoelectric energy harvesters. It is difficult to improve the transduction coefficient of the commercial PZT based piezoelectric ceramics due to the same variation trend of piezoelectric charge coefficient and dielectric constant with chemical modifications. In this work, Bi₂O₃ and Fe₂O₃ co-modified ((Pb_1-xBi_x)((Zr_0.53Ti_0.47)_1-xFe_x)O₃) ceramics were prepared by conventional solid state reaction method, and their dielectric and piezoelectric properties were studied. The piezoelectric charge coefficient d₃₃ increases by Bi and Fe co-modifications due to the enlarged grain size and reduced lattice distortion, while the dielectric constant ε₃₃ deceases mainly owing to the increased micro-pores in grains, leading to the enhancement transduction coefficient d₃₃×g₃₃. The Curie temperature Tc and maximum transduction coefficient d₃₃×g₃₃ are 346 °C and 17169 × 10^?15 m²/N, respectively, which are both higher than those of commercial PZT and PZN-PZT based piezoelectric ceramics. This work provides a new way to enhance the transduction coefficient of PZT based ceramics for piezoelectric energy harvesters used in wide temperature range.     

Revisiting the structural stability and electromechanical properties in lead zinc niobate-lead titanate-barium titanate (PZN-PT-BT) ternary system

Lead zinc niobate-lead titanate (PZN-PT) system is of particular interest for scientific researches and commercial applications due to the unique relaxation feature and superior electromechanical responses. However, it is difficult to prepare polycrystalline ceramics near the morphotropic phase boundary due to the stability of a competing lead niobate pyrochlore phase. BaTiO₃ (BT) was reported to be an effective perovskite phase stabilizer at a cost of reduction in Curie temperature and piezoelectric properties. Herein, the amount of BT in PZN-PT-BT system and the sintering conditions were optimized to simultaneously stabilize the perovskite phase and maintain high dielectric and piezoelectric response. An optimum piezoelectric coefficient d₃₃ ∼ 870 pC/N along with a T_m ∼ 133 °C and an electromechanical coupling coefficient k₃₃ ∼ 0.61 was obtained in the PZN-8PT-6BT ceramics sintered at 1100 °C. The low sintering temperature, wide processing window, and improved dielectric and piezoelectric properties make PZN-PT-BT ceramics potential candidates for piezoelectric devices.     

Enhanced Piezoelectric Properties and Thermal Stability in the (K0.5Na0.5)NbO3:ZnO Lead‐Free Piezoelectric Composites

The piezoelectric properties of (K_0.5Na_0.5)NbO₃ (KNN) are normally enhanced by chemical substitutions or doping to form solid solutions. In this study, we report that the piezoelectric properties of KNN and thermal stability of piezoelectric coefficient d₃₃ can be both enhanced by forming the composite of KNN:ZnO. The d₃₃ of KNN:0.2ZnO can be improved to 110 pC/N by introducing the ZnO nanoparticles, which is better than the pure KNN (d₃₃ = 85 pC/N). The Curie temperature (T_C = 407°C) remains well comparable to the pure KNN (T_C = 408°C). Furthermore, the thermal stability of both remanent polarization (P_r) and piezoelectric parameter (d₃₃) is improved. The enhanced thermal stability could be related to the induced built‐in electric field or the enhanced sinterability by the addition of ZnO. The present results may help to optimize the piezoelectric properties of lead‐free materials by forming composite.     

Effect of repeated composite sol infiltrations on the dielectric and piezoelectric properties of a Bi0.5(Na0.82K0.18)0.5TiO3 lead free thick film

Bi_0.5(Na_0.82K_0.18)_0.5TiO₃ lead free thick films have been produced using a combination of screen printing and subsequent infiltration of corresponding composite sol. Their structure, dielectric, ferroelectric and piezoelectric properties were investigated with variation in the number of composite sol infiltrations and the nanopowder loading in composite sol. Dielectric constant, remanent polarization, and piezoelectric coefficient have been shown to increase with increasing numbers of composite sol infiltration. Dielectric and ferroelectric properties of the thick films are found to be strongly dependent on the powder concentration of composite sols. The resulting 40 μm thick films infiltrated with 1.5 g/ml composite sols have maximum relative permittivity of 569 (at 10 kHz), remanent polarization of 21.3 μC/cm², coercive field of 80 kV/cm, and longitudinal effective piezoelectric coefficient d_33eff of 109 pm/V. The performance of these lead free piezoelectric thick films is comparable to the corresponding bulk ceramics.     

Lead-free LiNbO3 nanowire-based nanocomposite for piezoelectric power generation

In a flexible nanocomposite-based nanogenerator, in which piezoelectric nanostructures are mixed with polymers, important parameters to increase the output power include using long nanowires with high piezoelectricity and decreasing the dielectric constant of the nanocomposite. Here, we report on piezoelectric power generation from a lead-free LiNbO₃ nanowire-based nanocomposite. Through ion exchange of ultra-long Na₂Nb₂O₆-H₂O nanowires, we synthesized long (approximately 50 μm in length) single-crystalline LiNbO₃ nanowires having a high piezoelectric coefficient (d₃₃ approximately 25 pmV^-1). By blending LiNbO₃ nanowires with poly(dimethylsiloxane) (PDMS) polymer (volume ratio 1:100), we fabricated a flexible nanocomposite nanogenerator having a low dielectric constant (approximately 2.7). The nanogenerator generated stable electric power, even under excessive strain conditions (approximately 10⁵ cycles). The different piezoelectric coefficients of d₃₃ and d₃₁ for LiNbO₃ may have resulted in generated voltage and current for the e₃₃ geometry that were 20 and 100 times larger than those for the e₃₁ geometry, respectively. This study suggests the importance of the blending ratio and strain geometry for higher output-power generation in a piezoelectric nanocomposite-based nanogenerator.

PACS

77.65.-j; 77.84.-s; 73.21.Hb     

Effects of thermal strain on electric properties of lead zirconate titanate thin films upon LaNiO3 coated base metal plates

Electric properties for ferroelectric lead zirconate titanate (PZT50/50, 45/55, 40/60, 30/70) thin films on base metal plates with different thermal expansion coefficient (TEC) were calculated by a phenomenological model. Results show that when the TEC of substrates increases, dielectric constant, tunability and piezoelectric coefficient d₃₃ of all PZT thin films with tetragonal phase are decreased due to the larger compressive thermal strain. PZT50/50 thin films deposited on smaller TEC substrates can achieve higher dielectric constant, tunability and d₃₃. The computed dielectric constant of PZT50/50 thin films is in accordance with the measured results from sol-gel experimental process, and the trend of dielectric constant of PZT films adjacent to morphotropic phase boundary (MPB) derived from some references also agrees with that from calculation. These results suggest that higher tunability and d₃₃ of PZT films can be obtained by choosing smaller TEC substrates.     

Pyroelectric,ferroelectric, piezoelectric and dielectric properties of Na0.5Bi0.5TiO3 ceramic prepared by sol-gel method

Sodium bismuth titanate (BNT) nanopowder of molar composition 50/50 (Na_0.5Bi_0.5TiO₃) was prepared by a sol-gel processing method. The structure and microstructure of the precursor gel as well as the ferroelectric, pyroelectric, dielectric and piezoelectric properties of the BNT were studied. BNT crystallized in the rhombohedra perovskites structure Na_0.5Bi_0.5TiO₃ was obtained from the precursor gel by heating at 700 °C for 2 h in air. The BNT ceramic at 1100 °C sintering temperature present high crystallinity, good dielectric properties at 1 kHz (ε′=885, tan δ=0.03, T_c=370 °C), piezoelectric properties (k₃₃=0.39, c₃₃=105 GPa, e₃₃=12.6 C/m², d₃₃=120 pC/N), high remnant polarization (P_r=47 μC/cm²) and pyroelectric coefficient ($p$=707 μC/m² K) and low coercive field (E_c=55 kV/cm). Hence, the BNT prepared by sol-gel method could be used for silicon based memory device application where a low synthesis temperature is a key requirement.     

Synchronous improvement of piezoelectric property and temperature stability in PSN-PMN-PT ceramics by forming composites with ZnO

Relaxor ferroelectric materials with high piezoelectric properties always suffer from low phase transition temperature, making them difficult to satisfy the demands for high-temperature environment applications. In this work, we proposed a composite approach to improve the piezoelectricity and temperature stability of PSN-PMN-PT ceramics at the same time. The ZnO nanoparticles as a second phase were introduced into the PSN-PMN-PT matrix to form composite ceramics. When the ZnO content reaches 5 mol%, the piezoelectric constant d₃₃ increases from 529 pC/N for pure PSN-PMN-PT ceramic to 590 pC/N. Meanwhile, the retained d₃₃ after annealing at 200 °C keeps 92% of the value before annealing, indicating the thermal depolarization behavior is suppressed by the composite method. The synchronous improvement of the d₃₃ and thermal depolarization behavior for PSN-PMN-PT/ZnO composite ceramics is related to the local electric field and stress field caused by the addition of ZnO particles. Our results pave a simple and effective way to develop next-generation PT-based relaxor ferroelectric ceramics.     

Piezoelectric and Dielectric Properties of Acrylonitrile Butadiene Rubber/Lead Magnesio-Niobate Piezoelectric Ceram

A new composite with special piezoelectric property was prepared by using lead magnesio-niobate piezoelectric ceram powders (PMN) as dispersing phase in acrylonitrile butadiene rubber (NBR) matrix. The dielectric and piezoelectric properties of the composite were studied. The result shows that the particle size of 80% of PMN ceram powders was 0.5–2 µm. The piezoelectric constant (d₃₃) of the composite increased with increasing volume fraction of PMN, and the max piezoelectric constant is 33 when the PMN volume fraction is 85%. Appropriate delay of polarizing time with increasing polarizing voltage could be helpful to improve the d₃₃ value. The optional polarizing condition is 25 min, 7–8 kv/mm, and 80°C. The dielectric constant increased with the increasing of the PMN volume fraction. Polarized time, polarized voltage, and polarized temperature have no effect on the dielectric constant.     

Pairing high piezoelectric properties and enhanced thermal stability in grain-oriented BNT-based lead-free piezoceramics

(Bi_0.5Na_0.5)TiO₃ (BNT)-based piezoceramics usually exhibit enhanced piezoelectric coefficient d₃₃ together with the deterioration of depolarization temperature T_d, which is the common drawback limiting their use in practical application. Here, we demonstrate that harnessing the microstructure in BNT-based ceramics will be an efficient way to resolve this obstacle. <00l> oriented piezoelectric ceramics 0.94(Bi_0.5Na_0.5)TiO₃ ?0.06BaTiO₃ was engineered by templated grain growth (TGG) using NaNbO₃ (NN) as templates. The manufactured textured ceramics with the optimized microstructure was characterized by not only approximately 200% enhancement in the magnitude of piezoelectric response (d₃₃~297pC/N) but also improved thermal stability (T_d~57?°C) in comparison to its randomly oriented counterparts (d₃₃~151pC/N and T_d~32?°C). Moreover, the enhanced piezoelectricity in grain oriented specimens primarily originated from a high degree of non-180° domain switching as compared to the randomly axed ones. The current study opens the door to pair high piezoelectric properties and enhanced thermal stability in BNT-related materials though texture technique.     

Ultrahigh-performance [001]-oriented porous PZT-5H single crystal grown by the solid state crystal growth method

Porous PZT-5H single crystals are grown by the solid state crystal growth (SSCG) method. The microstructure, phase structure and dielectric/piezoelectric properties are investigated for [001]-oriented porous PZT-5H single crystal. Evolution of phase structure with temperature is researched using in-situ temperature-dependent X-ray diffraction. The effect of pores on performance parameters is simulated using COMSOL Multiphysics® software. Ultrahigh piezoelectric coefficient d₃₃ of up to about 1700 pC/N and effective piezoelectric coefficient d₃₃* of up to about 3700 pm/V at 5 kV/cm are obtained. Moreover, the effective piezoelectric coefficient d₃₃* is stable around 1900 pm/V under 3 kV/cm and 5 kV/cm in the temperature range of 70–160 °C. Importantly, the sample possess an extremely large figure of merit g₃₃*d₃₃ (111 × 10⁻¹² m²/N), which is related to the presence of pores in the single crystal. This work expands the scope of PZT based single crystal and highlights their significant application possibilities in piezoelectric energy harvester, and actuator at high temperature.     

Processing and piezoelectric properties of porous PZT ceramics

5–45% porous lead zirconate titanate (PZT) ceramics were fabricated by adding pore formers such as polymethyl methacrylate (PMMA) and dextrin and sintering at 1200 °C for 2 h. The optimum heating procedure was decided according to the thermogravimetric analysis of pore formers. The effects of different pore formers and their content on the microstructure and piezoelectric properties were investigated. With an increase in the content of pore formers, the porosity of sintered ceramics increased, which led to reduced dielectric constant (ɛ₃₃) and longitudinal piezoelectric coefficient (d₃₃) as well as enhanced hydrostatic piezoelectric voltage coefficient (g_h) and hydrostatic figures of merit (d_h g_h). The hydrostatic figures of merit (d_h g_h) of 41% porous PZT were 10 times more than that of 95% dense PZT.     

Enhanced piezoelectric properties and temperature stability of Bi4Ti3O12-based Aurivillius ceramics via W/Nb substitution

Bi₄Ti₃O₁₂ (BIT), a typical Aurivillius ceramics with high Curie temperature (T_c ? 675 °C), has great potential for high temperature applications. This work provides an effective method of inducing structure distortion, relieving the tetragonal strain of the TiO₆ octahedron and decreasing the concentration of oxygen vacancies to improve the piezoelectricity and temperature stability of BIT ceramics. Bi₄Ti_2.98W_0.01Nb_0.01O₁₂ possesses an optimum piezoelectric coefficient (d₃₃) of 32 pC/N, a high T_c of 655 °C and a large resistivity of 3 × 10⁶ Ω·cm at 500 °C. The maximum d₃₃ reported here is approximately quadruple than that of pure BIT (?7 pC/N). Moreover, the d₃₃ of W/Nb co-doped BIT and the in-situ temperature stability of the compression-mode sensor present a highly stable characteristic in the range of 25–600 °C. These results imply that W/Nb-modified BIT ceramics is a promising candidate for application at high temperatures of up to 600 °C.     

Achievement of high electric performances for bismuth titanate-based piezoceramics via hot press sintering

Bi₄Ti₃O₁₂ (BIT) ceramic has great potential in high-temperature environment due to its high Curie temperature T_C ~ 675 °C. In this work, hot press sintering (HPS) is applied on the 0.01 mol Ce and Nb/Cr co-doped BIT (BCTNC) ceramics to enhancing the low piezoelectric coefficient (d₃₃ < 7 pC/N) and resistivity. Extremely high d₃₃ (~39 pC/N) together with high T_C (~672 °C) and high dc resistivity ρ (~1.49 ×10⁷ Ω?cm at 500 °C) are obtained in HPS samples. The enhancement of piezoelectricity benefits from high density of domain and high poling electric field. Moreover, outstanding thermal stability of piezoelectric constant (d₃₃ ~ 35 pC/N after annealing at 650 °C) and low dielectric loss (tanδ ~ 3.8% at 500 °C) are observed as well. These findings are instrumental in understanding HPS and provide a possible manipulation of crystallized mechanism and domains growing kinetics to enhance piezoelectric performances of BIT based ceramics.     

Ultra-high-temperature piezoelectric responses and ultra-high thermal stability of piezoelectricity in ceramic PbZr0.54Ti0.46O3

To date, most piezoceramics with a high piezoelectric coefficient (d₃₃ > 500 pC/N) and a high Curie temperature (T_C around 400°C) are BiScO₃-PbTiO₃-based (BS-PT-based) systems, containing the rare-earth element Sc, whose high cost hinders mass production. We investigated the effect of Nd-doping on the morphotropic phase boundary and synthesized low-cost Nd-doped PbZr_0.54Ti_0.46O₃ (PZT) piezoceramics, achieving high piezoelectric performance. At room temperature, the piezoelectric coefficient d₃₃ reached 550 pC/N with a T_C = 375°C and this changed by only 3.6% over a broad temperature range (30–260°C). The d₃₃ value reached an ultra-high value of 941 pC/N at 345°C, which is higher than that of a BS-PT-based ceramic (810 pC/N at 350°C). The developed PZT ceramic material has a superior electrostrictive strain of 0.45% at 40 kV/cm, and a room temperature piezoelectric coefficient d₃₃* of 1312 pm/V at 20 kV/cm. Our research provides a new paradigm for designing piezoceramics that can be used over a wide temperature range.     

Temperature-driven phase transitions and enhanced piezoelectric responses in Ba(Ti0.92Sn0.08)O3 lead-free ceramic

Ferroelectric phases coexistence or transition is an important strategy on generating high piezoelectricity. Here, the temperature-induced phase structural evolution correlated with small signal piezoelectric response d₃₃, bias-field piezoelectric activity d^max₃₃(E), unipolar and bipolar strain piezoelectric outputs d^*₃₃ in Ba(Ti_0.92Sn_0.08)O₃ (BTS0.08) ceramic was investigated in details. Temperature-driven successive phase transitions from rhombohedral (R) to orthorhombic (O), tetragonal (T), finally to cubic (C) phases took place around 14?°C, 38?°C and 61?°C, respectively. The highest d₃₃ value of 675 pC/N is achieved in the T-C phase transition. However, the O-T phase boundary gives the highest d^max₃₃ =?1170?p.m./V, bipolar d^*₃₃ =?822?pm/V and unipolar d^*₃₃ =?1318?pm/V. The temperature-driven phase transition exhibits large enhancements in piezoelectric property comparable to that of composition-induced phase boundary. These features suggest an effective method to design high-performance piezoelectrics by tailoring the types of phase boundary.     

Grain growth anomaly and piezoelectric properties of liquid phase sintered high TC 0.36BiScO3 - 0.64PbTiO3 ceramics with sillenite Bi12PbO19

The sintering behavior of 0.36BiScO₃-0.64PbTiO₃ (0.36BS-0.64 PT) ceramics was studied to investigate the effect of grain growth by the sillenite Bi₁₂PbO₁₉ (BP) phase on their piezoelectric properties for application in high-temperature piezoelectric devices. The BP phase formed during calcination at temperatures <750 °C led to a grain growth anomaly of the 0.36BS-0.64 PT ceramics sintered at 1000 °C. This phase assisted the grain growth of the 0.36BS-0.64 PT ceramics by liquid phase sintering. In particular, the 0.36BS-0.64 PT ceramic calcined at 700 °C exhibited excellent piezoelectric properties with a d₃₃ of 531 pC/N, g₃₃ of 41×10⁻³ Vm/N, k_p of 61.8%, and Q_m of 16. In addition, the 0.36BS-0.64 PT ceramics exhibited ferroelectric relaxor-like characteristics with an extremely large relaxation coefficient (γ) of 1.94 along with high maximum dielectric permittivity temperature (426 °C).     

Enhanced transduction coefficient in piezoelectric PZT ceramics by mixing powders calcined at different temperatures

Large transduction coefficient ($d_{33}\times g_{33}$) is difficult to obtain in piezoelectric ceramics because these two parameters show opposite trends with compositional modifications. Herein, the Pb(Zr_0.53Ti_0.47)O₃ ceramic powders were calcinated under different temperatures (A:830 °C, B:860 °C, and C:890 °C), and then mixed together according to different weight ratios (1A:1B:1C, 1A:2B:1C, 1A:2B:3C and 3A:2B:1C) for ceramics preparation. Both d₃₃ and g₃₃ are improved successfully, and the transduction coefficient with the weight ratio of 1A:2B:3C reaches up to 17,500 × 10⁻¹⁵ m²/N, which is 60 % higher than that with the powders calcinated under 830 °C, and at least twice those of commercial PZT-4, PZT-5A and PZT-8 ceramics. The improved transduction coefficient is owing to the enhanced piezoelectric constant and spontaneous polarization resulted from the increased grain size, relative density and the fraction of tetragonal phase. These results indicate that this is a simple but effective way to tailor the transduction coefficient in piezoelectric ceramics.     

High‐temperature piezoelectric properties of 0‐3 type CaBi4Ti4O15:x wt%BiFeO3 composites

The 0‐3 type CaBi₄Ti₄O₁₅:30 wt%BiFeO₃ composite shows much better high‐temperature piezoelectric properties than the single‐phase CaBi₄Ti₄O₁₅ or BiFeO₃ ceramics. The composite with 0‐3 type connectivity exhibits a high density of 7.01 g/cm³, a saturated polarization of 21.5 μC/cm² and an enhanced piezoelectric d₃₃ of 25 pC/N. After the poled composite was annealed at 600°C, its d₃₃ is 21 pC/N at room temperature. Resistance of the composite decreases slowly from 10⁹ ohm at 20°C to ~10⁵ ohm at 500°C. Furthermore, the poled composite shows strong radial and thickness dielectric resonances at 20°C‐500°C.     

Growth orientation-related enhancement of electrical properties in (Na0.85K0.15)0.5Bi0.5TiO3-based composite films

TiO₂-coated (Na_0.85K_0.15)_0.5Bi_0.5TiO₃ (NKBT) composite films with thicknesses of 250 nm and 650 nm are synthesized on Pt(111)/Ti/SiO₂/Si using an aqueous sol-gel method. X-ray diffraction (XRD) in ω-scan and ψ-scan modes is performed to study the crystal orientation of the films. The electrical properties of the TiO₂-coated NKBT composite films are investigated over a temperature range from -150 °C to150 °C. Compared to films without the TiO₂ layer, the TiO₂-coated NKBT films exhibit enhanced electrical properties, higher temperature stability, and better endurance performance, which can be ascribed to the combined effects of the highly (100)-preferred orientation and improved degree of crystallization. The composite film in which TiO₂ layers are attached on both sides of the 650 nm-thick NKBT film demonstrates the best ferroelectric performance with the highest remnant polarization (P_r) of 24.2(±1.2) μC/cm² under 750 kV/cm, the best piezoelectric performance with the highest effective piezoelectric constant (d₃₃^*) of 82(±4) pm/V, and the best electric performance with the lowest leakage current density of 4.5 × 10⁻⁶(±0.4 × 10⁻⁶) A/cm² at 20 V. Piezoresponse force microscopy (PFM) further confirms the enhanced ferroelectricity and domain switching of the TiO₂-coated composite films on a microscopic scale. In addition, the P_r values of the films increase gradually as the temperature decreases from 150 °C to-150 °C, while the d₃₃^* values exhibit the opposite trend, which is mainly attributed to the suppressed mobility of thedomain walls at low temperatures.