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.     

Boosting transduction coefficient in BaTiO3-Based piezoceramic through phase boundary engineering

Transduction coefficient (d₃₃×g₃₃) is the core parameter for evaluating piezoelectric energy harvesting materials. However, due to the thermodynamic constraints, the synergistic variation between piezoelectric charge constant (d₃₃) and dielectric constant (ε_r) indeed hinder the further increase of d₃₃×g₃₃. Herein, an enhanced d₃₃×g₃₃ of 13,000 × 10^?15 m²/N was achieved in 0.80BaTiO₃-0.10CaTiO₃-0.10BaZrO₃ (BC_0.1ZT) lead-free solid solution for the first time through a phase boundary engineering strategy. The high d₃₃×g₃₃ mainly stems from non-synergistic variation of dielectric and piezoelectric performance in the rhombohedral-orthorhombic (R-O) phase boundary, in which the low ε_r comes from the increased domain size and reduced domain wall density; while the high configurational sensitivity of the unique domains to external electric field contributed to the high d₃₃. Our findings provide an alternative approach for enhanced energy harvesting performance by tracing the strategy of designing phase boundary to decouple d₃₃ and ε_r.     

Giant electric field-induced strain at room temperature in LiNbO3-doped 0.94(Bi0.5Na0.5)TiO3-0.06BaTiO3

We report experimental investigation on the ferroelectricity and electric field-induced strain response in LiNbO₃-doped 0.94(Bi_0.5Na_0.5)TiO₃-0.06BaTiO₃ (BNT-BT) piezoelectric ceramics. At room temperature, a large strain of 0.6% (at 70 kV/cm) is achieved in the 2.5%-LiNbO₃-doped BNT-BT, higher than that of commercially-utilized Pb(Zr,Ti)O₃. The corresponding piezoelectric coefficient d^*₃₃ reaches 857 pm/V, which is high among these of BNT-based ceramics at room temperature. Further study indicates that the superior piezoelectric properties are realized at the ferroelectric-relaxor transition temperature T_F-R, which is pushed to room temperature with 2.5% LiNbO₃ doping. This indicates that large electromechanical response can be induced via delicate mixing of the ferroelectric rhombohedral phase and the polar nanoregions (PNRs) relaxor-ferroelectric tetragonal phase.     

An experimental model for predicting the piezo and dielectric constant of PVDF-PZT nanocomposite fibers with 0–3 and 1–3 connectivity

Energy harvesting from mechanical energy around ambient by flexible nanogenerators is one of the most efficient ways to generate green and renewable energy. Lead zirconate titanate (PZT) particles were embedded into a polyvinylidene fluoride (PVDF) polymer matrix to prepare mixed 0–3 and 1–3 connectivity nanocomposite fibers by electrospinning method. Various theoretical models of Maxwell-Garnett, Rayleigh, and Tinga etc were presented at two different Classes to predict the dielectric constant of PVDF-PZT nanocomposite fibers and compared the predicted results with the experimental results. Also, the piezoelectric properties like the piezoelectric coefficient (d₃₃) and piezoelectric voltage coefficient (g₃₃) were predicted by the Furukawa model and the predicted values were compared with the experimental values. Finally, the experimental model was derived to predict the dielectric constant of binary composites with mixed 0–3 and 1–3 connectivity. Compared to well-known models, the proposed experimental model accurately predicted the dielectric constant of PVDF-PZT nanocomposite fibers. The highest and lowest difference between the theoretical and the experimental results were obtained 12.24% and 0.12% for PZT volume fractions 1.1 and 17, respectively. Also, due to the linear relationship between the dielectric constant and piezoelectric coefficients, this model was generalized to predict the piezoelectric coefficients.     

Synthesis and Characterization of Bowl-Like Single-Crystalline BaTiO3 Nanoparticles

Novel bowl-like single-crystalline BaTiO₃ nanoparticles were synthesized by a simple hydrothermal method using Ba(OH)₂·8H₂O and TiO₂ as precursors. The as-prepared products were characterized by XRD, Raman spectroscopy, SEM and TEM. The results show that the bowl-like BaTiO₃ nanoparticles are single-crystalline and have a size about 100–200 nm in diameter. Local piezoresponse force measurements indicate that the BaTiO₃ nanoparticles have switchable polarization at room temperature. The local effective piezoelectric coefficient d₃₃ ^* d_{33}^{ * } is approximately 28 pm/V.     

Lead germanium oxide sinter-assisted PZT composite thick films

Thick films of niobium doped lead zirconate titanate (PNZT) were prepared from a sol-gel/PZT powder composite slurry. The effects of adding different amounts of sol-gel derived lead germanium oxide (PGO) as sintering aid were examined. Four layers of composite, with intermediate sol infiltrations, were deposited by spinning onto Pt/Ti/SiO₂/Si substrates followed by drying and annealing. Addition of PGO enhanced the densification process at a temperature as low as 770 °C. It resulted in an increase in the film properties that depended upon the level of PGO addition. Film properties were assessed by measuring the capacitance and dielectric loss. d_33,f and e_31,f piezoelectric coefficient measurements were carried out after poling at 10 V/μm for 5 min at 130 °C. A maximum relative permittivity of 500 was observed between 5 and 8 wt.% PGO addition. The maximum in d_33,f was found to be about 40 pC/N. Additions between 7 and 10 wt.% PGO led to the maximum e_31,f piezoelectric coefficient of about −1.5 C/m².     

Structure,dielectric and piezoelectric properties of Ba0.90Ca0.10Ti1−xSnxO3 lead-free ceramics

Lead-free piezoelectric ceramics Ba_0.90Ca_0.10Ti_1−xSn_xO₃ have been prepared by a conventional ceramic fabrication technique and the effects of Sn⁴⁺ on the structure, dielectric and piezoelectric properties of the ceramics have been investigated. All the ceramics exhibit a pure perovskite structure. After the substitution of Sn⁴⁺, the crystal structure of ceramics is transformed gradually from a tetragonal to an orthorhombic phase, and becomes a pseudo-cubic phase at x≥0.14. The substitution also decreases the Curie temperature greatly from 138 °C at x=0 to 33 °C at x=0.12, and shifts the orthorhombic–tetragonal phase transition to higher temperatures. Coexistence of the orthorhombic and tetragonal phases is formed in the ceramic at x=0.10, leading to significant improvements in the piezoelectric properties: d₃₃=521 pC/N and k_p=45.5%. Our results also reveal that the ceramics sintered at higher temperatures contain larger grains, and thus exhibit more noticeable tetragonal–orthorhombic phase transition and enhanced ferroelectric and piezoelectric properties.     

High electromechanical strain properties by the existence of nonergodicity in LiNbO3–modified Bi1/2Na1/2TiO3–SrTiO3 relaxor ceramics

This study investigated the effect of LiNbO₃ modification on the dielectric, ferroelectric and electromechanical strain properties of Bi_1/2Na_1/2TiO₃–SrTiO₃ (BNT–ST) lead–free relaxor ceramics. The sintering temperature for lead–free BNT–ST relaxor ceramics was slightly decreased from 1175?°C to 1050?°C by modifying with LiNbO₃. We found that the sintering temperature affects the dielectric behavior of 0.76BNT–(0.24?x)ST–xLiNbO₃ (BNST–100xLN) ceramics at high temperature (near dielectric maximum temperature, T_m). The T_m for the low–temperature sintered sample was shifted to relatively higher temperature by comparison with the high–temperature sintered samples. Furthermore, the degradation of dielectric behavior near T_m in low–temperature sintered BNST–2LN ceramics was revealed after poling treatment and seem to be related to the existence of a high temperature stabilized nonergodic relaxor phase. Accordingly, we assume that the stabilized nonergodic relaxor phase is responsible for the relatively late transition from ferroelectrics to the relaxor. Therefore, we obtained the improved d₃₃^* of 616?pm/V as the highest value in low–temperature sintered BNST–2LN ceramics.     

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.     

Piezoelectric voltage constant and sensitivity enhancements through phase boundary structure control of lead-free (K,Na)NbO3-based ceramics

The piezoelectric voltage constant (g₃₃) is a material parameter critical to piezoelectric voltage-type sensors for detecting vibrations or strains. Here, we report a lead-free (K,Na)NbO₃ (KNN)-based piezoelectric accelerometer with voltage sensitivity enhanced by taking advantage of a high g₃₃. To achieve a high g₃₃, the magnitudes of piezoelectric charge constant d₃₃ and dielectric permittivity ε_r of KNN were best coupled by manipulating the intrinsic polymorphic phase boundaries effectively with the help of Bi-based perovskite oxide additives. For the KNN composition that derives benefit from the combination of ε_r and d₃₃, the value of g₃₃ was found to be 46.9 × 10^?3 V·m/N, which is significantly higher than those (20 – 30 × 10^?3 V·m/N) found in well-known polycrystalline lead-based ceramics including commercial Pb(Zr,Ti)O₃ (PZT). Finally, the accelerometer sensor prototype built using the modified KNN composition demonstrated higher voltage sensitivity (183 mV/g) when measuring vibrations, showing a 29% increase against the PZT-based sensor (142 mV/g).     

Dielectric and piezoelectric properties of (1−x)(Bi,Na)TiO3–x(Bi,K)TiO3 lead-free ceramics for piezoelectric energy harvesters

The piezoelectric and dielectric properties of the (1−x)(Bi,Na)TiO₃–x(Bi,K)TiO₃ (x=0.12, 0.14, 0.18, 0.20 and 0.30) lead-free ceramics were investigated. Specimens were prepared by the conventional mixed oxide method and sintered at 1170 °C in air. Scanning electron microscopy indicated that increasing x from 0.12 to 0.30 causes a decrease in the grain size. The (1−x)(Bi,Na)TiO₃–x(Bi,K)TiO₃ ceramics shows a homogeneous microstructure and excellent dielectric and piezoelectric properties. Specimens with optimum composition showed a piezoelectric charge constant d₃₃ of 166 pC/N, an electromechanical coupling factor k_p of 0.5, a dielectric constant ε_r of 1591.32 at 1 kHz and generated power output of 37.49 nW/cm².     

Critical roles of the rhombohedral-phase inducers in morphotropic NaNbO3-BaTiO3-ABO3 quasi-ternary lead-free piezoelectric ceramics

A morphotropic phase boundary (MPB) between rhombohedral (R) and tetragonal (T) phases was identified in a few (0.9-x)NaNbO₃-0.1BaTiO₃-xABO₃ (x?=?0–0.05) lead-free systems. Critical roles of R-phase inducers were specially evaluated in terms of phase boundary position, microstructure and piezoelectric responses. The results indicate not only the tolerance factor of the ABO₃ additive but also its ferroelectricity and corresponding volume change would influence the formation of phase boundary and further determine dielectric and ferroelectric responses. The piezoelectric coefficient d₃₃ of MPB compositions was compared with theoretically-calculated d_33-cal according to d₃₃?=?2P_r·ε₃₃·Q₃₃, demonstrating that the piezoelectric response of these systems should be determined by combined effects of the phase coexistence, nano-scale domains and particularly enhanced dielectric responses. The largest d₃₃ ～305 pC/N, the highest ε₃₃^T/ε_o ～2815 and the lowest P_r ～14.7 μC/cm² were achieved in the MPB composition with 3.75% SrZrO₃. These experimental results provide a valuable reference for designing new NaNbO₃-based lead-free piezoelectric materials.     

Reduced dielectric loss and high piezoelectric constant in Ce and Mn co-doped BiScO3-PbCexTi1-xO3-Bi(Zn0.5Ti0.5)O3 ceramics

MnO₂-doped 0.99(0.36BiScO₃-0.64PbTi_1-xCe_xO₃)-0.01Bi(Zn_0.5Ti_0.5)O₃ (BS-PTC-BZT-MnO₂) ceramics are fabricated by the solid-state method. Here, it's firstly reported that Ce element can reduce dielectric loss (tan δ) and suppress the decrease of piezoelectric constant (d₃₃) simultaneously. Effects of Ce contents on the structure and electrical properties of BS-PTC-BZT-MnO₂ ceramics are studied. The ceramics (x?=?0.02) with MPB (rhombohedral-tetragonal) possess low dielectric loss (tan δ?=?1.36%, 1?kHz) and high piezoelectric constant (d₃₃ =?360 pC/N) simultaneously, which is superior to most reported BS-PT. Besides, excellent comprehensive properties including high Curie temperature (T_C =?422?°C), large dielectric constant (?_r =?1324), and high remnant polarization (P_r =?35.1?µC/cm²) are obtained. Asymmetric S-E and P-E hysteresis loops indicate that defects and oxygen vacancies are induced by multi-valence elements (Ce and Mn), which is the origin for reducing tan δ. In addition, good thermal stability of piezoelectric and dielectric properties is observed. These results indicate that Ce and Mn co-doped BS-PTC-BZT-MnO₂ ceramics can be well applied as power electronic devices under high temperature.     

Improved piezoelectricity of lead-based PNN-PIN-PT ternary ceramics via polymorphic nanodomain modulation

High-performance piezoelectric materials are widely used in electromechanical applications such as sensors, actuators, and transducers. Herein, improvement in electrical properties of Pb(Ni_1/3Nb_2/3)O₃−Pb(In_1/2Nb_1/2)O₃−PbTiO₃ relaxor ferroelectrics by modulating the polymorphism of nano-scale domain is reported, and piezoelectric coefficients d₃₃ and d₃₃* as high as 948 pC/N and 1108 pm/V, respectively, are achieved. The high piezoelectric response is elucidated by combining cryogenic dielectric, Rayleigh analysis, and scanning electron microscopy with piezoresponse force microscope. During the transition from the tetragonal to rhombohedral phase, the morphology of the ferroelectric domains changes significantly, mesoscopic domain destruction is observed, and thus nano-scale domains appear as an extrinsic contribution of piezoelectricity. In addition, nano-scale domains promote polarization rotation, thus, improving the piezoelectric response. The improved piezoelectric performance demonstrates good thermal stability, retaining the inverse piezoelectric coefficient of approximately 1000 pm/V near 70 °C. This work provides a good example of improving ceramics' piezoelectric response by modulating the polymorphism of nanoscale domains.     

Effect of Zr/Ti ratio on piezoelectric properties of Pb(Ni1/3Sb2/3)O3-Pb(ZrTi)O3 ceramics

Piezoceramic compositions [Pb(Ni_1/3Sb_2/3)]_0.02-[Pb(Zr_1−yTi_y)]_0.98O₃ with y = 0.46-0.50 were synthesized by solid state route to study the effect of Zr/Ti ratio on crystal structure, microstructure, piezoelectric and dielectric properties. Calcination was performed at 1060 °C. The specimens were sintered at 1280 °C for 1 h. X-ray diffraction studies indicate the co-existence of tetragonal and rhombohedral perovskite phases in these compositions. Microstructural analysis showed the dense and uniform microstructure for [Pb(Ni_1/3Sb_2/3)]_0.02-[Pb(Zr_0.52Ti_0.48)]_0.98O₃. This composition was resulted in optimum values of properties viz. charge constant (d₃₃ = 301 × 10⁻¹² C/N), voltage constant (g₃₃ = 33.7 × 10⁻³ V m/N), product of piezoelectric charge constant and voltage constant (d₃₃ × g₃₃ = 10.12 × 10⁻¹² C V m/N²) and coupling factor (k_p = 0.63). Results indicated that this material composition could be suitable for power harvesting and sensor applications.     

Grain size effect on electrical properties of Mn-modified 0.67BiFeO3–0.33BaTiO3 lead-free piezoelectric ceramics

To investigate how grain size affects the dielectric, ferroelectric, and piezoelectric properties of Mn-modified 0.67BiFeO₃–0.33BaTiO₃ ceramics, we prepared samples with a wide variety of grain sizes from 4.1 μm to 0.59 μm via a conventional solid-state process that use the normal and the two-step sintering methods. Small-signal dielectric measurements show that all the samples exhibit a relaxor-like behavior and that grain size has little influence on the room-temperature dielectric permittivity. For grain sizes below 2 μm, the remanent polarization P_r and piezoelectric coefficient d₃₃ decrease with the grain size, whereas they remain almost constant near P_r = 27 μC/cm² and d₃₃ = 70 pC/N in samples with grain sizes exceeding 2 μm. The mechanism underlying the observed grain size effect is discussed in terms of the electric-field-induced formation of macroscopic ferroelectric domains.     

Effect of tungsten on the structure and piezoelectric properties of PZN–PZT ceramics

0.2PZN–0.8PZT ceramics with pure perovskite structure were prepared by the two-step method with the addition of 0–1.5 wt.% WO₃ and their piezoelectric properties were investigated. The WO₃ addition influences the lattice structure and W⁶⁺ will replace B-site ions of perovskite, which will lead to the decrease of the lattice constant. Compared to the increase of the dielectric constant (ɛ) and mechanical quality factor (Q_m), the values of coercive electric field (E_c), remnant polarization (P_r), electromechanical coupling factor (K_p), and piezoelectric constant (d₃₃) decrease with increasing WO₃ addition. The composition with 1.0 wt.% of WO₃ addition on 0.2PZN–0.8PZT ceramics exhibits excellent piezoelectric properties, showing great promise as practical materials for high power piezoelectric devices.     

Effects of Sm-substitution on dielectric,ferroelectric, and piezoelectric properties of 0.36(Bi1-xSmx)ScO3-0.64PbTiO3 ceramics

Dielectric, ferroelectric, and piezoelectric properties of 0.36(Bi_1-xSm_x)ScO₃-0.64PbTiO₃ (BSPT-xSm) ceramics were investigated to assess effects of Sm-substitution on 0.36BiScO₃-0.64PbTiO₃ for high temperature piezoelectric device application. Optimal sintering was achieved at 1200°C when the BSPT-xSm ceramics were fully densified and crystallized with a perovskite structure without any secondary phase. The substitution of Bi³⁺ with Sm resulted in degradation of rhombohedral side in BSPT-xSm ceramics having morphotropic phase boundary. In addition, variations of grain size and ferroelectric behavior after Sm-substitution were insignificant. However, dielectric constant (ε^T₃₃/ε₀) was significantly enhanced with an increasing of amount of Sm to 5%. Although a slight decrease of relative density in case of x exceeding 3% led to deterioration of piezoelectric values of d₃₃, k_p, and d₃₃*, the BSPT-3%Sm ceramic exhibited excellent values of d₃₃ of 628 pC/N, k_p of 62.4%, and d₃₃* of 718 pm/V at 4.5 kV/mm, along with a high ferroelectric transition temperature of 421°C. The highly increased diffusion coefficient of 1.909 also implies that the Sm-substitution contributed to relaxor-like ferroelectric behavior of BSPT ceramics.     

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.     

Magnetoelectricity in CoFe2O4 nanocrystal-P(VDF-HFP) thin films

Transition metal ferrites such as CoFe₂O₄, possessing a large magnetostriction coefficient and high Curie temperature (T_c > 600 K), are excellent candidates for creating magnetic order at the nanoscale and provide a pathway to the fabrication of uniform particle-matrix films with optimized potential for magnetoelectric coupling. Here, a series of 0–3 type nanocomposite thin films composed of ferrimagnetic cobalt ferrite nanocrystals (8 to 18 nm) and a ferroelectric/piezoelectric polymer poly(vinylidene fluoride-co-hexafluoropropene), P(VDF-HFP), were prepared by multiple spin coating and cast coating over a thickness range of 200 nm to 1.6 μm. We describe the synthesis and structural characterization of the nanocrystals and composite films by XRD, TEM, HRTEM, STEM, and SEM, as well as dielectric and magnetic properties, in order to identify evidence of cooperative interactions between the two phases. The CoFe₂O₄ polymer nanocomposite thin films exhibit composition-dependent effective permittivity, loss tangent, and specific saturation magnetization (M_s). An enhancement of the effective permittivity and saturation magnetization of the CoFe₂O₄-P(VDF-HFP) films was observed and directly compared with CoFe₂O₄-polyvinylpyrrolidone, a non-ferroelectric polymer-based nanocomposite prepared by the same method. The comparison provided evidence for the observation of a magnetoelectric effect in the case of CoFe₂O₄-P(VDF-HFP), attributed to a magnetostrictive/piezoelectric interaction. An enhancement of M_s up to +20.7% was observed at room temperature in the case of the 10 wt.% CoFe₂O₄-P(VDF-HFP) sample.