The structural origin of enhanced energy harvesting performance in piezoelectric perovskite

Energy harvesting, which can translate the wasted vibration energy into electric energy, is now a hot topic in the field of new energy, and the key point is to design high power piezoelectric ceramic according with the requirements of low-frequency vibration energy harvesting. In this study, high quality Co-modified 0.2Pb(Zn_1/3Nb_2/3)O₃–0·8Pb(Zr_0·50Ti_0·50)O₃ (PZN–PZT+Co) ceramics have been prepared by the two-stage method, and the energy harvesting characteristics were investigated. The results showed that the hierarchical nanodomain structure boosts the strong piezoelectric activity, leading to the high energy harvesting performance. The PZN–PZT+Co ceramic sintered at 1000 °C exhibits an excellent d₃₃ × g₃₃ value of 14080 × 10^?15 m²/N, which are much larger than that of commercial PZT-based ceramics. In the mode of the cantilever-type energy harvester, the output voltage and energy density of 33 V, 4.4 μW/mm³ were obtained at a low resonance frequency of 85 Hz and acceleration of 10 m/s², showing potential application in piezoelectric energy harvester.     

Improved Li and Sb doped lead-free (Na,K)NbO3 piezoelectric ceramics for energy harvesting applications

Piezoelectric energy harvesting is the most widely investigated technology for renewable energy applications. In this work, (1-x)(Na_0.5K_0.5)NbO₃-xLiSbO₃ piezoelectric ceramics were prepared through conventional mixed oxide fabrication methods with different sintering temperatures. Although the (Na_0.5K_0.5)NbO₃ piezoelectric material is representative among the lead-free ceramics, it is difficult to densify by typical sintering techniques owing to its easy evaporation properties of potassium (K⁺) and sodium ion (Na⁺). Hence, lithium (Li⁺) and antimony ion (Sb⁵⁺) were used for the partial substitution of (Na_0.5K_0.5)NbO₃. With the optimized sintering temperature, Li⁺ and Sb⁵⁺ are expected to be crucial in increasing the density and enhance the piezoelectric and ferroelectric properties. In this study, the phase, microstructure, and dielectric and electrical properties of (1-x)(Na_0.5K_0.5)NbO₃-xLiSbO₃ ceramics depending on the sintering temperature is examined by employing X-ray diffraction, field emission scanning electron microscopy, impedance analyzer, and mechanical force system for energy harvesting.     

A flexible piezoelectric pressure sensor based on PVDF nanocomposite fibers doped with PZT particles for energy harvesting applications

Flexible piezoelectric energy harvesters are a suitable choice for scavenging wasted mechanical energy because of the high demand for sustainable power sources. Flexible pressure sensors based on PVDF-PZT nanocomposite with different PZT volume fractions (0.011, 0.041, 0.096, 0.17, 0.3, and 0.37) were prepared in the form of fibers through an electrospinning method for piezoelectric energy harvesting application. According to the results, dielectric constant and piezoelectric coefficients (e.g. piezoelectric coefficient, and figure of merit) gradually increased with the doping of PZT particles into PVDF fibers. Dielectric constant (ϵ), piezoelectric coefficient (d), and figure of merit (d × g) for PVDF-PZT nanocomposite with 0.011 PZT volume fraction were 37.29, 10.51 pCN⁻¹, and 33.46 × 10⁻¹⁶ m²/N, respectively, and increased to 104.81, 22.93 pCN⁻¹, and 56.68 × 10⁻¹⁶ m²/N for PVDF-PZT nanocomposite fibers with a volume fraction of 0.37. As piezoelectric energy harvesters, piezoelectric sensitivity of PVDF-PZT nanocomposite fibers rose with increasing the PZT volume fraction. The generated output voltage was 184 mV under an applied force of 2.125 N with the piezoelectric sensitivity calculated as 173.507mV/Nμm for PVDF-PZT nanocomposite fibers with 0.37 PZT volume fractions which increased compared to pristine PVDF fibers (generated output voltage = 22 mV under applied force 2.4 N, piezoelectric sensitivity = 29.49 mV/Nμm). The achieved output power density of PVDF-PZT nanocomposite fibers with 0.37 PZT volume fractions was obtained 30.69μW cm⁻² higher than PVDF-PZT nanocomposite fibers with 0.011 PZT volume fractions (18.44μW cm⁻²).     

Flexible piezoelectric energy harvesters with graphene oxide nanosheets and PZT-incorporated P(VDF-TrFE) matrix for mechanical energy harvesting

Flexible piezoelectric energy harvesters (PEHs) have attracted extensive interest because of their ability to transform mechanical energy into electric power. Here, PEHs were fabricated using P(VDF-TrFE)-based piezoelectric composite films containing lead zirconate titanate (PZT) powder and –OH-functionalized graphene (HOG) nanosheets (HOG-P/P). Among all composites, a high open-circuit voltage (Voc) of approximately 50 V_p-p and a maximum power density of 1.4 μW/cm² were obtained from a HOG-P/P PEH with 0.10 wt% HOG nanosheets and 15 wt% PZT under bending–releasing mode. Moreover, the PEH exhibited a stable voltage output after 3000 bending–releasing cycles. In addition, the PEH harvested mechanical energy from human body movements and generated an output voltage and current of 60 V and 8 μA during the finger bending–releasing process, lighting up 30 commercial white LEDs. The enhanced piezoelectric performance can be attributed to the introduction of HOG nanosheets and PZT powder. This work provides an effective strategy for improving the output performance of P(VDF-TrFE)-based PEHs.     

BiScO3-PbTiO3 piezoelectric ceramics with Bi excess for energy harvesting applications under high temperature

0.36BiScO₃-0.64PbTiO₃ ceramic is a competitive piezoelectric material even though it contains lead and volatile Bi contents. It contains a relatively decreased lead content compared to that of the Pb(Zr,Ti)O₃ system but it has similar piezoelectric properties with high Curie temperature. However, due to the very volatile component of Bi the 0.36BiScO₃-0.64PbTiO₃ system has Bi-deficient composition. Therefore, in order to compensate for deficient Bi contents in the 0.36BiScO₃-0.64Pb,TiO₃ system, excess 0.005, 0.01, 0.015 and 0.02 mol of Bi were added to the ceramics to enhance the piezoelectric properties for the first time. By employing excess Bi addition, the piezoelectric charge coefficient, electromechanical coupling factor, output open circuit voltage, and generated output power density were improved from 417 pC/N, 51.48%, 19.69 V and 0.28 mJ/cm³ to 452 pC/N, 52.25%, 26.93 V and 0.48 mJ/cm³. We expect that piezoelectric properties of 0.36BiScO₃-0.64PbTiO₃ ceramics were improved by adding Bi excess.     

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.     

Evaluation of the pore morphologies for piezoelectric energy harvesting application

Piezoelectric energy harvesting has attracted significant attention in recent years due to their high-power density and potential applications for self-powered sensor networks. In comparison to dense piezoelectric ceramics, porous piezoelectric ceramics exhibit superiority due to an enhancement of piezoelectric energy harvesting figure of merit. This paper provides a detailed examination of the effect of pore morphology on the piezoelectric energy harvesting performance of porous barium calcium zirconate titanate 0.5Ba(Zr_0.2 Ti_0.8)O₃-0.5(Ba_0.7Ca_0.3)TiO₃ (BCZT) ceramics. Three different pore morphologies of spherical, elliptical, and aligned lamellar pores were created via the burnt-out polymer spheres method and freeze casting. The relative permittivity decreased with increasing porosity volume fraction for all porous BCZT ceramics. Both experimental and simulation results demonstrate that porous BCZT ceramics with aligned lamellar pores exhibit a higher remanent polarization. The longitudinal d₃₃ piezoelectric charge coefficient decreased with increasing porosity volume fraction for the porous ceramics with three different pore morphologies; however, the rate of decrease in d₃₃ with porosity is slower for aligned lamellar pores, leading to the highest piezoelectric energy harvesting figure of merit. Moreover, the peak power density of porous BCZT ceramics with aligned lamellar pores is shown to reach up to 38 μW cm^-2 when used as an energy harvester, which is significantly higher than that of porous BCZT ceramics with spherical or elliptical pores. This work is beneficial for the design and manufacture of porous ferroelectric materials in devices for piezoelectric energy harvesting applications.     

Piezoelectric properties of (1-x)BZT-xBCT system for energy harvesting applications

In this study, we investigated (1-x)Ba(Zr_0.2Ti_0.8)O₃–x(Ba_0.7Ca_0.3)TiO₃ lead-free piezoelectric ceramics for energy harvester applications. The (1-x)BZT-xBCT ceramic is a promising lead-free piezoelectric material in the field of piezoelectric energy harvesting. Piezoelectric and energy properties of (1-x)BZT-xBCT ceramics were analyzed to confirm the possibility of using them as energy-harvesting materials. Especially, the vicinity of the phase convergence region was investigated to improve their piezoelectric properties. In the phase convergence region, cubic, rhombohedral, orthorhombic, and tetragonal regions co-exist within the narrow region. Near the phase transition region between the orthorhombic and tetragonal phase, the highest piezoelectric property d₃₃?=?464 pC/N and the highest energy density of 158.5 μJ/cm³ were observed. This output energy density of 158.5 μJ/cm³ is the recorded highest value among lead-free ceramics. We found that the optimal sintering temperature was 1475?°C and the optimal composition was BZT-0.5BCT.     

High room-temperature pyroelectric property in lead-free BNT-BZT ferroelectric ceramics for thermal energy harvesting

Pyroelectrics are attracting increasing attention because they enable pyroelectric generators to extract energy from low-gradient-temperature heat for portable electronic devices. High pyroelectric coefficient around room temperature is essential for high-performance energy harvesters, which, unfortunately, is only commonly achieved in lead-based ferroelectrics. Herein we report a high room temperature pyroelectric response of 27.2 × 10^?4 C m^-2 K^-1 in 0.94(Bi_0.5Na_0.5)TiO₃-0.06Ba(Ti_0.75Zr_0.25)O₃ lead-free ceramics by modulating the Zr⁴⁺/Ti⁴⁺ ratio to tune the ferroelectric-relaxor antiferroelectric-like phase transition point to around ambient temperature, whose pyroelectric response is one order of magnitude higher than that of the sample without Zr and even comparable to those of lead-containing pyroelectrics. The theoretical analysis revealed that introduced Zr⁴⁺ could incorporate into the TiO₆ octahedral lattices and break the long-range translational symmetry of BaTiO₃ lattices, resulting in the reduction of B-site ion displacement activation energy and transition point of ferroelectric-relaxor antiferroelectric-like phase, giving rise to a pronounced room-temperature pyroelectric effect in BNT-BZT.     

High energy storage efficiency and large electrocaloric effect in lead-free BaTi0.89Sn0.11O3 ceramic

Lead-free BaTi_0.89Sn_0.11O₃ (BTSn) ceramic was elaborated via a solid-state reaction method and its dielectric, ferroelectric, energy storage, electromechanical as well as electrocaloric properties were investigated at 25 kV/cm. Pure perovskite structure was confirmed by X-ray diffraction analysis. The maximum of the dielectric constant was found to be 17390 at 41 °C. The enhanced total energy density, the recovered energy density, and the energy storage efficiency of 92.7 mJ/cm³, 84.4 mJ/cm³, and 91.04 %, respectively, were observed at 60 °C. In contrast, the highest energy storage efficiency of 95.87 % was obtained at 100 °C. At room temperature, the electromechanical strain and the large-signal piezoelectric coefficient reached a maximum of 0.07 % and 280 pm/V. The large electrocaloric effect of 0.71 K and the electrocaloric responsivity of 0.28 × 10^-6 K mm/kV at 49 °C under 25 kV/cm were indirectly determined via Maxwell approach and the measured ferroelectric polarization P(E,T). The electrocaloric response was also modelled by exploiting the Landau-Ginzburg-Devonshire (LGD) phenomenological theory. The modelling result of 0.61 K at 50 °C under 25 kV/cm supports the experimental findings. We conclude that BTSn lead-free ceramic is a promising candidate for potential applications in high-efficiency energy storage devices and solid-state refrigeration technology.     

Efficiency of energy harvesting and storage using a multilayer capacitor based on BaTi0.86Sn0.14O3 ferroelectric lead-free ceramics

The study of the parameters of energy harvesting and storage in the lead-free solid solution BaTi_0.86Sn_0.14O₃ (BTSnO) was performed. The permittivity shows the behavior similar to a diffuse phase transition with the critical exponent γ = 1.84, which is close to the value characteristic of relaxors. Large values of the recoverable energy density, W_rec=(5.8–7.0)?104 J/m³, and the energy storage efficiency coefficient, η=(82–94) %, are implemented in a wide temperature range, 30–87°С, at a low electric field, E = 18.5 kV/cm. For the first time, the analysis of the Olsen cycle was performed using two phase diagrams: polarization – electric field and entropy – temperature. A fairly good agreement was found between the values of the energy conversion density, N_D ≈ 0.15 J/cm³, which was determined using two approaches. A universal parameter is proposed for comparing the energy harvesting density for the materials studied in different ranges of temperature and electric fields.     

Tailoring properties of (Bi0.51Na0.47)TiO3 based dielectrics for energy storage applications

Lead free dielectric ceramics of 0.65Bi_0.51Na_0.47Ti_1-5x/4Nb_xO₃- 0.35Ba(Ti_0.7Zr_0.3)O₃ (BB35-100xNb, x = 0.00, 0.01, 0.02, 0.04 and 0.08) are fabricated by conventional solid-state sintering method for potential energy storage applications. Benefited from the coexistence of relaxor and antiferroelectric features, a high recoverable energy storage density of 3.2 J/cm³, together with high energy efficiency of 93%, is simultaneously achieved in bulk BB35-1Nb ceramic at the critical electric field of 280 kV/cm. The studied BB35-1Nb ceramic exhibits a wide temperature usage range of 20–160 °C with energy density variation below 3%, and excellent cycling reliability with both energy density and efficiency variations less than 4% over 10⁶ cycles, together with its fast discharge time of ˜1.2 μs, making BB35-1Nb ceramic promising candidate for high-temperature, high power energy storage applications.     

Self‐adaptive piezoelectric ceramic vibration system based on asymmetric piezoelectric cantilever for energy harvesting

Micropower energy harvesting is one of key technologies for the micromation and practical development of wireless sensor and communication node networks. A self‐adaptive piezoelectric vibration system based on modified homogeneous strain asymmetric PZT piezoelectric ceramic cantilever beam for the micropower energy harvesting was designed and prepared. A vertical cantilever was designed at the first time to obtain the homogeneous state of stress which can largely increase the power output and energy harvesting efficiency of piezoelectric cantilevers. In order to achieve the self‐adaptive vibration, the asymmetric structure was adopted. Asymmetric cantilevers moved horizontally and changed the length of main cantilevers when affected by the variation in external frequency excitation, thus, the switching of resonant frequency was archived automatically without dissipating additional energy.     

Li and Ta-modified KNN piezoceramic fibers for vibrational energy harvesters

Piezoelectric energy harvesters (PEH) hold enormous potential for converting mechanical energy from our surrounding environment into electrical energy that can be used for powering portable electronics. Potassium sodium niobate (KNN) is one of the promising alternatives to replace lead-based piezoelectric materials. This work presents a cutting-edge demonstration of synthesis-function-device integration of piezoelectric nanofibers, where the morphology and the composition are engineered towards achieving high device output. We report a flexible nanogenerator based on electrospun Li and Ta-modified lead-free KNN nanofibers yielding a high voltage output of 5.6 V, which is around 9-fold higher than for the Mn-doped KNN nanofibers reported previously. The influence of Li and Ta-incorporation into the KNN lattice on the electromechanical coupling and the effect of a nanofiber morphology are investigated. The net-shaped KNN and Li and Ta-modified KNN nanofibers, synthesized by electrospinning of appropriate sols, maintain their structural integrity upon calcination and firing steps. The phase analysis (XRD) confirms the formation of single-phase (KNN) material. Li and Ta are found to be incorporated on the A and B-sites of the perovskite lattice, respectively. Piezo force microscopy data show the heat-treated nanofibers to exhibit multi-domain ferroelectric properties.     

Phase-formation,microstructure, and piezoelectric/dielectric properties of BiYO3-doped Pb(Zr0.53Ti0.47)O3 for piezoelectric energy harvesting devices

This paper proposes a method for the composition and synthesis of lead zirconate titanate (PZT) piezoelectric ceramic for use in energy harvesting systems. The proposed material consists of (1?x)Pb(Zr_0.53Ti_0.47)O₃–xBiYO₃ [PZT–BY(x)] (x=0, 0.01, 0.02, 0.03, 0.04, and 0.05 mol) ceramics near the morphotropic phase boundary (MPB) region, prepared by a solid-state mixed-oxide method. The optimum sintering temperature was found to be 1160 °C, which produced high relative density for all specimens (96% of the theoretical density). Second phases were found to precipitate in the composition containing x≥0.01 mol of BY. It is shown that the addition of BY inhibits grain growth, and exhibits a denser and finer microstructure than those in the un-doped state. Fracture surface observation revealed predominant intergranular fracture for x=0 and x=0.01, while a mixed mode of transgranular and intergranular fracture appeared for x≥0.02. The optimal doping level was found to be x=0.01, for which a dielectric constant (K₃₃^T) of 750, a Curie temperature (T_C) of 373 °C, a remnant polarization (P_r) of 50 µC/cm², a piezoelectric constant (d₃₃) of 350 pC/N, and an electro-mechanical coupling factor (k_p) of 65% were obtained. In addition, the piezoelectric voltage constant (g₃₃), and transduction coefficient (d₃₃×g₃₃) of PZT–BY(x) ceramics have been calculated. The ceramic PZT–BY(0.01) shows a considerably lower K₃₃^T value, but higher d₃₃ and k_p. Therefore, the maximum transduction coefficient (d₃₃×g₃₃) of 18,549×10^?15 m²/N was obtained for PZT–BY(0.01). The large (d₃₃×g₃₃) indicates that the PZT–BY(0.01) ceramic is a good candidate material for energy harvesting devices.     

Effect of pore size and porosity on piezoelectric and acoustic properties of Pb(Zr0.53Ti0.47)O3 ceramics

We studied the effect of porosity and pore morphology on the functional properties of Pb(Zr_0.53Ti_0.47)O₃ (PZT) ceramics for application in high frequency ultrasound transducers. By sintering a powder mixture of PZT and polymethylmetacrylate spherical particles (1.5 and 10?μm) at 1080°C, we prepared ceramics with ～30% porosity with interconnected micrometer sized pores and with predominantly ～8?μm spherical pores. The acoustic impedance was ～15?MRa for both samples, which was lower than for the dense PZT. The attenuation coefficient α (at 2.25?MHz) was higher for ceramics with ～8?μm pores (0.96?dB?mm^??1?MHz^??1), in comparison to the ceramic with smaller pores (0.56?dB?mm^??1?MHz^??1). The high α value enables the miniaturisation of the transducer, which is crucial for medical imaging probes. The dielectric and piezoelectric coefficients, polarisation, and strain response decreased with increased porosity and decreased pore/grain size. We suggest a possible role of pore/grain size on the switching behaviour.     

Improvement of piezoelectricity of (Na,K)Nb-based lead-free piezoceramics using [001]-texturing for piezoelectric energy harvesters and actuators

0.96(Na_0.5K_0.5)(Nb_0.93Sb_0.07)O₃?(0.04?x)BaZrO₃?x(Bi_0.5Ag_0.5)ZrO₃[NKNS?(0.04?x)BZ?xBAZ] ceramics are well textured along the [001] direction using 3.0 mol% NaNbO₃ seeds. The textured-NKNS?0.02BZ?0.02BAZ thick film has a rhombohedral-orthorhombic-tetragonal (R-O-T) structure with a large proportion of the O-R structure (> 80%). This specimen exhibits the largest values for d₃₃ (805 pC/N) and d₃₃ ×g₃₃ (29.5 ×10^?12 m²/N), which are the largest d₃₃ and d₃₃ ×g₃₃ values of NKN-based piezoceramics to date. It exhibits a large strain (0.17% at 4.0 kV/mm). Therefore, it is an outstanding piezoceramic material for piezoelectric energy harvesters (PEHs) and actuators. A PEH and actuator are fabricated using this specimen. The PEH shows a large power density (4.3 mW/cm³), which is the largest value among the PEHs produced by lead-free piezoceramics. The actuator exhibits a large acceleration (50.8 G) and displacement (3.9 mm), which are the best actuating properties among the actuators produced by lead-free piezoceramics. Therefore, texturing is an excellent technique for improving the piezoelectricity of NKN-based piezoceramics.     

A complex lead-free (Na,Bi, Ba)(Ti,Fe)O3 single phase perovskite ceramic with a high energy-density and high discharge-efficiency for solid state capacitor applications

We have investigated a series of compositions in the pseudo-ternary lead-free alloy system Na_1/2Bi_1/2TiO₃-BaTiO₃-BiFeO₃ with regard to its energy storage density and discharge efficiency. A composition 0.4(Na_0.5Bi_0.5TiO₃)-0.225BaTiO₃-0.375BiFeO₃ of this series was identified to give the best energy density and discharge efficiency. While conventional sintering gave energy density of 0.77 J/cm³ and discharge efficiency of 67%, we achieved a remarkable increase in energy storage density (∼1.4 J/cm³) and discharge efficiency (∼90%) by using spark plasma sintering of this composition. Our results suggest that this alloy system can be a potential lead-free candidate for high electric energy storage and discharge efficiency.     

Active polymer nanofibers for photonics,electronics, energy generation and micromechanics

Active polymer nanofibers for opto- and nano-electronics benefit from low cost and versatile fabrication processes and exhibit an unequaled flexibility in terms of chemical composition, physical properties and achievable functionality. For these reasons, they have rapidly emerged as powerful tool for nanotechnologies and as building blocks of a wide range of devices. Both bottom up and top down nanofabrication concepts were developed to produce nanofibers made of conjugated or other functional polymers and blends. This article summarizes and reviews the chemico-physical and functional requirements for polymer nanofibers to be used in opto- and nanoelectronics, as well as recent advances in various promising device architectures, such as light emitting and photovoltaic devices, photodetectors, field-effect transistors, piezo- and thermoelectric generators, and actuators. The outlook of functional polymer nanofibers and of devices based on them is also outlined and discussed.