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.     

Co-sintered PZT ceramics for the piezoelectric transformers

The co-sintered functionally graded PZT ceramic transformers working in a k_p-mode in both input and output circuits were studied. Theoretical model was developed to describe the transformation ratio as a function of the frequency. Transformation ratio, efficiency and power density are measured for the set of samples with homogenous PZT and variable input/output PZT compositions for the low-power signal and compared with the derived formulae. The maximum efficiency is observed for the homogenous hard PZT compositions (type APC840). Contrary to the theoretical calculations, co-sintering hard PZT ceramics along with the soft PZT were not experimentally proven to produce a noticeable increase in the transformation ratio, efficiency and output power density probably due to the difference in optimal sintering temperature.     

Giant piezoelectric coefficient of PNN-PZT-based relaxor piezoelectric ceramics by constructing an R-T MPB

xTa-PNN-PZT piezoelectric ceramics with [0.55 Pb(Ni_1/3Nb_2/3)O₃ - 0.45 Pb(Zr_0.3Ti_0.7)O₃ - xwt%Ta₂O₅] + 1 wt% PbO composition (0 ≤ x ≤ 0.7) were prepared by conventional solid-state reaction method. Special attention was paid to the effect of Ta₂O₅ concentration on structural, dielectric, piezoelectric, and ferroelectric properties of these ceramics. In particular, rhombohedral-tetragonal morphotropic phase boundary was observed in PNN-PZT crystal structure near the composition of x = 0.5. At this point, volume fraction of rhombohedral phase was almost equal to that of tetragonal phase. In addition, the ceramic exhibited the optimum values of piezoelectric coefficient, bipolar strain, unipolar strain, and inverse piezoelectric coefficient, i.e., 1090 pC/N, 0.135%, 0.165%, and 1493 pm/V, respectively. Moreover, according to in-situ X-ray diffraction, piezoelectric force microscopy, and in-situ strain measurement results, phase structure of 0.5Ta-PNN-PZT revealed relatively stable piezoelectric behavior at 60 °C.     

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.     

Large electrostrain at high temperature in bismuth sodium titanate-based piezoelectric ceramics

(1-x)[0.82Bi_0.5Na_0.5TiO₃-0.18Bi_0.5K_0.5TiO₃]-xAgNbO₃ ceramics (abbreviated as BNKT-100xAN, x = 0–0.06) are fabricated by the solid state reaction method. It is discovered that silver niobate is completely dissolved into the lattice of 0.82Bi_0.5Na_0.5TiO₃-0.18Bi_0.5K_0.5TiO₃ ceramics based on characterization. The relaxation mechanism and characteristics of BNKT-100xAN ceramics are analyzed by dielectric temperature spectra and AC impedance spectra. The content of ordered domains and PNRs of BNKT-4AN ceramics is optimum, which enables it possess excellent electrostrain of 0.51%. The electrostrain almost remain constant after the 10⁴ cycles test, suggesting that it also has great fatigue resistance. After polarization at high temperature, large electrostrain of 1.4% and inverse piezoelectric constants of 2004 pm/V are obtained at 150 °C in BNKT-4AN ceramics. The ultrahigh electrostrain is mainly promoted by the larger polarizability of the <111>-oriented and <001>-oriented defect dipoles, the same direction of defect dipoles and the spontaneous polarization direction of phase, the pinning effects of the defect dipoles on the PNRs and the collinear arrangement of the PNRs. This work indicates that lead-free piezoelectric ceramics is hopeful to be applied in piezoelectrics working at high temperature. Simultaneously, a new design paradigm also is provided for the preparation of piezoelectric ceramics with excellent performance.     

Enhanced piezoelectric properties and low electrical conductivity of Ce-doped Bi7Ti4.5W0.5O21 intergrowth piezoelectric ceramics

New types of Ce-doped Ce_xBi_7-xTi_4.5W_0.5O₂₁ (BTW-BIT-xCe) Aurivillius intergrowth ceramics with high Curie temperatures were synthesized to improve the piezoelectric performances as well as the conduction behaviour, and these ceramics exhibit great potential for high-temperature lead-free piezoelectric applications. The crystal structure, electrical properties and conduction behaviour of BTW-BIT-xCe samples were analysed thoroughly. The XRD patterns combined with Rietveld refinements of the patterns showed that the crystal structure transformed from orthorhombic structure towards pseudo-tetragonal structure with increasing CeO₂ dopant, indicating that a higher symmetry was obtained. The dielectric properties of Ce-doped samples were improved, accompanied by a significant drop in the dielectric loss and a slight decreased Curie temperature (705 °C–683 °C). An enhanced piezoelectric constant d₃₃ of 25.3 pC/N was obtained in BTW-BIT-0.12Ce, which may be attributed to a common decrease in the electrical conductivity and coercive field. Besides, a low electrical conductivity of 2 × 10^-6 S/cm at 540 °C was achieved in the same component owing to a decreased concentration of the oxygen vacancies, which was verified by analyses on XPS spectra. The above results indicate that Ce-doped BTW-BIT samples have great development potential for high temperature piezoelectric applications.     

Enhanced piezoelectric properties and temperature-insensitive strain behavior of <001>-textured KNN-based ceramics

In this study, <001>-textured 0.99(K_0.5Na_0.5)_0.95Li_0.05Nb_0.93Sb_0.07O₃−0.01CaZrO₃ [abbreviated as 0.99KNLNS-0.01CZ] lead-free ceramics were prepared by templated grain growth (TGG) using plate-like NaNbO₃ templates and sintered by a two-step sintering process with different soaking time. All textured samples with high Lotgering factor (f >85%) presented orthorhombic and tetragonal coexisting phase, and the proportion of orthorhombic phase was varied with prolonged soaking time. A large piezoelectric constant d₃₃ (~ 310 pC/N) was obtained in the textured samples with a 12 h soaking time, which was almost twice larger compared to the randomly oriented one. Furthermore, the field-induced piezoelectric strain coefficient d₃₃^*(~ 440 pm/V) of the textured ceramics with 6 h soaking time was larger than the value of randomly oriented one (~ 298 pm/V) at room-temperature. Enhanced piezoelectric response and good temperature stability prove that <001>-textured 0.99KNLNS-0.01CZ ceramics are promising candidates in the field of lead-free piezoelectric materials.     

A novel piezoelectric ceramic with high Curie temperature and high piezoelectric coefficient

0.02Pb(Sb_1/2Nb_1/2)O₃-0.98Pb_1-xBa_x(Zr_0.53Ti_0.47)O₃ (PSN-PB_xZT) ceramics with high Curie temperature and high piezoelectric properties were prepared by traditional solid state reaction measurement to meet the requirements for high temperature applications, and the crystal structure, dielectric, piezoelectric and ferroelectric properties were investigated. All the samples show a tetragonal crystal structure at room temperature and there was no noticeable change with the increasing of Ba²⁺ content. Doping of Ba²⁺ markedly improved piezoelectric properties of PSN-PZT, the maximum d₃₃~560 pC/N, T_c ~317 °C at x = 0.05. Their outstanding piezoelectric properties will drive the development of high temperature industrial applications.     

Enhanced transduction coefficient and thermal stability of 0.75BiFeO3-0.25BaTiO3 ceramics for high temperature piezoelectric energy harvesters applications

Owing to the coexistence of high depolarization temperature of 500 °C and good piezoelectric properties, 0.75BiFeO₃-0.25BaTiO₃-0.5mol%MnO₂ (BFBTMn) ceramics show potential energy harvesting applications at elevated temperature. Chemical modifications are usually difficult to improve transduction coefficient (d₃₃×g₃₃) due to the opposite directions of d₃₃ and g₃₃. Herein, the BFBTMn ceramic powders with different average grain sizes of 500 (S₁), 700 (S₂) and 800 (S₃) nm were mixed together for ceramics preparation. This method promotes the grain size, relative density and rhombohedral phase volume fraction of BFBTMn ceramics, leading to the much improved piezoelectric transduction coefficient and its thermal stability. The transduction coefficient of ceramics with optimized weight ratio (1S₁:2S₂:1S₃) reaches up to 4644 × 10^?15 m²/N, about 51% higher than those without mixed powder and at least 60% higher than those reported in the literatures, while its degradation from room temperature to 500 °C is about 15%, much smaller than that (30%) of ceramics without mixed powders. These investigations pave a new way to tailor the transduction coefficient and its thermal stability of BF-BT piezoelectric ceramics for high temperature energy harvesting devices.     

Processing and enhanced electrical properties of Sr1-x(K0.5Bi0.5)xBi2Nb2O9 lead-free piezoelectric ceramics

Lead-free piezoelectric ceramics, Sr_1−x(K_0.5Bi_0.5)_xBi₂Nb₂O₉ (SKBN-x, x=0, 0.2, 0.5, 1.0), were synthesized by a conventional solid-state reaction. Structural and electrical properties of SKBN-x ceramics were investigated. X-ray diffraction analysis suggested that the substitution led to the formation of a layered perovskite structure. Plate-like morphologies for the grains were clearly observed in all the samples, which are characteristic for layer-structure Aurivillius compounds. The Curie temperature (T_c) is found to shift to higher temperature from 445 °C to 509 °C with increasing (K, Bi) content. Excellent remanent polarization (2P_r∼15 μC/cm²) were obtained for SKBN-0.2 ceramic. High piezoelectric coefficient of d₃₃∼21  pC/N were obtained for the samples at x=0.5. Additionally, thermal annealing studies indicated that the piezoelectric coefficient (d₃₃) of SKBN-0.5 was unchanged even if annealing temperature increased to be 450 °C, demonstrating the ceramics are the promising candidates for high-temperature applications.     

Enhanced pyroelectric and piezoelectric responses in W/Mn-codoped Bi4Ti3O12 Aurivillius ceramics

The pyroelectric and piezoelectric properties of 4 at% Mn-doped Bi₄Ti_2.9W_0.1O₁₂ (BiTW-Mn) Aurivillius ceramic were investigated and compared to Bi₄Ti_2.9W_0.1O₁₂ (BiTW) counterpart, which were fabricated using a conventional solid state reaction method. High resistivities of 4.9?×?10¹² and 2.5?×?10¹¹ Ω?cm at 100?°C were obtained in the W-doped and W/Mn-codoped BiT ceramics, respectively. They showed similar activation energies and ionic-p-type mixed conduction mechanisms. Higher pyroelectric coefficients of 57.1?μC/m²K and piezoelectric coefficients of 21 pC/N, as well as much lower dielectric loss of 0.003 were achieved in W/Mn-codoped ceramics. These property changes were mainly induced by $\text{M}{\text{n}}_{\text{Ti}}^{}?{\text{V}}_{\text{o}}^{}$ defect dipoles. The effect of acceptor doping was evidenced by an internal bias field, shown by a horizontal offset in the polarization-field behavior. The improved properties together with high thermal stability indicate that BiTW-Mn may be a promising candidate for pyroelectric and piezoelectric devices at elevated temperatures.     

Evaluation of the complex material constants of piezoelectric ceramics in the thickness vibration mode

A new noniterative method, for determining the dielectric, piezoelectric and elastic constants, in complex form, for piezoceramic materials, in the thickness extensional mode, was proposed.This method is very flexible, as it is based on the standard approach to determine the elastic stiffness, followed by the measurement of the impedance at two frequencies to calculate the dielectric and piezoelectric constants, by solving a system of two equations.The new method was tested on materials with various thickness coupling factors (k_t = 4.5–60%) and mechanical quality factors (Q_mt = 20–1600), proving very good accuracy for all of them.The accuracy of standard method was also evaluated for the same materials.     

Enhanced piezoelectricity and high-temperature sensitivity of Zn-modified BF-BT ceramics by in situ and ex situ measuring

Effect of Zn addition on microstructure, electrical properties and temperature stability and sensitivity of piezoelectric properties for 0.7Bi_1-xZn_xFeO₃ −0.3BaTiO₃ (abbreviated as BZxF–BT) ceramics was investigated. The improved piezoelectric properties, high-temperature stability and high-temperature sensitivity by in situ and ex situ measuring were obtained by moderate Zn addition. It was demonstrated that the enhancement piezoelectric properties can be attributed to poling induced texturization degree of ferroelectric domains and increased rhombohedral structural distortions. It was proposed that the depoling temperature where the induced small signal piezoelectricity disappears stemmed from the detexturization of preferred orientation domains. The improved piezoelectric responses and high-temperature sensitivity could be attributed to the thermally activated preferred orientation domains. The good piezoelectric properties together with high-temperature stability suggest that BZxF–BT system is a promising material for high temperature piezoelectric applications.     

Large piezoelectric coefficient with enhanced thermal stability in Nb5+-doped Ba0.85Ca0.15Zr0.1Ti0.9O3 ceramics

Chemical doping is an indispensable tool to tailor the properties of the commercial piezoelectric materials. However, a high piezoelectric coefficient with enhanced thermal stability is rarely achieved by one dopant in some high-performance ferroelectrics, e.g., the recently discovered eco-friendly (Ba_0.85Ca_0.15)(Zr_0.1Ti_0.9)O₃ (BCZT) ceramics. In order to optimize the piezoelectric property in BCZT system by a simple way, we investigated the doping effect of Fe³⁺, Nb⁵⁺ and Bi³⁺ cations in BCZT ceramics respectively. The results indicate that only Nb⁵⁺-doped BCZT ceramics display a combination of large piezoelectric coefficient and enhanced thermal stability, compared with others. Moreover, the established phase diagrams and in-situ transmission electron microscope (TEM) observations reveal that such optimized piezoelectric properties after Nb⁵⁺ doping originates from (i) the low polarization anisotropy near the ambient tetragonal (T)-orthorhombic (O) phase transition and (ii) the easy domain wall motion of persistent miniaturized ferroelectric domains upon heating.     

Synthesis routes for enhanced piezoelectric properties in spark plasma sintered Ta-doped KNN ceramics

Ta substitution in K_0.5Na_0.5NbO₃ lead free piezoelectrics helps to prevent grain growth and has been shown to improve the piezoelectric properties but always leads to hetereogeneous microstructures. Two synthesis routes have been studied to prepare K_0.5Na_0.5Nb_0.8Ta_0.2O₃ (KNNTa) substituted powders. Then highly densified KNNTa ceramics have been obtained by spark plasma sintering (SPS). The use of a synthesized oxide precursor Nb_1.6Ta_0.4O₅ during the ceramic elaboration process clearly shows through accurate Rietveld study a successful Ta substitution with 92% of Amm2 K_0.485(8)Na_0.515(8)Nb_0.819(6)Ta_0.181(6)O₃ phase, confirmed by SEM-EDS analysis and a more homogeneous chemical composition. This leads to enhanced electromechanical coupling coefficients with an improvement of 50% of k_t, 15% for k_p and low electrical losses, compared to the conventional synthesis method with a simple mixing of commercial precursors.     

Enhancing piezoelectric properties of Ba0.88Ca0.12Zr0.12Ti0.88O3 lead-free ceramics by doping Co ions

The piezoelectric properties of lead-free Ba_0.88Ca_0.12Zr_0.12Ti_0.88O₃ (BCZT) ceramics were greatly optimized by doping Co ions using a CoO powder. The role of Co²⁺ and Co³⁺ in enhancing the piezoelectric properties and the relationship between the content ratio Co³⁺/Co²⁺ and piezoelectric performance were studied. The X-ray diffraction patterns of all samples indicated that crystalline phases were a BCZT-based single perovskite structure regardless of the Co ion content. The phase transition temperature and lattice distortion degree were related to the Co ion content and the content ratio Co³⁺/Co²⁺ because Co²⁺ resulted in higher oxygen vacancy generation, whereas Co³⁺ induced larger lattice shrinkage. The ceramic containing 0.10 wt% of Co ion showed the best piezoelectric and dielectric performance with the highest piezoelectric constant d₃₃ ~ 490 p.m./V at room temperature and the highest Curie temperature T_c of 110 °C, which increased by 29% and 16%, respectively. In this case, the content ratio Co³⁺/Co²⁺ reached the maximum value of 0.86. The high piezoelectric properties and phase stability of BCZT ceramics by doping Co ions make these ceramics promising piezoelectric materials for practical applications.     

Effects of slurry composition on the properties of 3-1 type porous PZT ceramics prepared by ionotropic gelation

In this study, 3-1 type lead zirconate titanate (PZT) ceramics with one-dimensional pore channels were produced by ionotropic gelation process of alginate/PZT suspensions. By increasing the sodium alginate concentration from 1.0wt% to 3.0 wt%, the alginate/PZT suspensions turned from Newtonian to non-Newtonian behavior with substantial increase in apparent viscosity. Accordingly, 3-1 type PZT ceramics with porosity decreasing from 56.78% to 41.44% were obtained, while the pore size distribution became non-uniform gradually. Based on the structural features, the 3-1 type PZT ceramics possessed much higher relative permittivity (ε_r) than that of 3-0 or 3-3 type PZT ceramics with similar porosities. Increase in the porosity led to a moderate decline in the longitudinal piezoelectric strain coefficient (d₃₃), a reduction in the dielectric loss factor (tan δ), and a high value of hydrostatic strain coefficient (d_h). As a result, the 3-1 type PZT ceramics possessed a maximal hydrostatic figure of merit (HFOM) value of 5597×10^–15 Pa⁻¹ when the porosity was 56.78%, which may be of help for low frequency hydrophones applications.     

Simultaneously enhanced piezoelectric response and piezoelectric voltage coefficient in textured KNN‐based ceramics

<001> ‐textured 0.99(K_0.49Na_0.49Li_0.02)(Nb_0.97‐xSb_0.03Ta_x)O₃‐0.01CaZrO₃ [abbreviated as 0.99KNLN_0.97‐xST_x‐0.01CZ, x = 0.03, 0.07, 0.10, 0.15, 0.20, 0.25] ceramics were prepared by templated grain growth (TGG) method and a two‐step sintering process. Giant longitudinal piezoelectric coefficient d₃₃ (391 pC/N) and piezoelectric strain coefficient d₃₃* (630 pm/V under an AC E‐field of 20 kV/cm) can be obtained in the textured ceramics with x = 0.25. All textured ceramics display superior k_p (>54%) and g₃₃ (>23 × 10^?3 Vm/N) which are in an order of magnitude with PZT ceramics. The maximum value of k_p (~63.3%) obtained in textured ceramics with x = 0.15 is higher than that of famous textured LF4 ceramics. Excellent comprehensive properties suggest that <001> ‐textured 0.99KNLN_0.97‐xST_x‐0.01CZ ceramics are promising candidates in the field of lead‐free piezoelectric materials.     

Enhancement of piezoelectric and ferroelectric properties of BaTiO3 ceramics by aluminum doping

Ferroelectric and piezoelectric properties of BaTiO₃ and Al-doped BaTiO₃ ceramics were investigated. The ferroelectric study demonstrated that, by doping Al³⁺ ions in the A-site of BaTiO₃, the polarization–electric field loop exhibited enhanced remnant polarization (from 12 to 17.5  μC/cm²), saturation and switching. In addition, the piezoelectric constant (d₃₃) increased with Al-doping for both static and dynamic strain values (from 75 to 135 and from 29.2 to 57.9 pC/N, respectively, at a maximum applied electric field of 16 kV/cm). Furthermore, the dielectric constant values increased and both the dielectric loss factor and leakage current decreased, even though the transition temperature shifted to lower temperature (from 121 to 113 °C) for the Al-doped sample. Therefore, the Al-doped BaTiO₃ has adjustable piezoelectric and ferroelectric properties.     

Hard/soft effects of multivalence co-dopants in correlation with their location in PZT ceramics

Piezoelectric hard/soft effects of multivalence co-dopants (Sb and Mn) in correlation with their location in the lattice, were investigated in PZT ceramics, prepared by conventional ceramic technology, with the following compositions: Pb_0.98Sr_0.02 ((Ti_0.49Zr_0.51)_1-0.015-xMn_0.015Sb_x)O₃ with x = 0, 0.005, 0.01, 0.02, 0.03, where antimony was initially assumed to substitute for Ti/Zr ions. The antimony valence state was found to be +3 in all samples by X-ray Photoelectron Spectroscopy investigations. The Electron Paramagnetic Resonance spectra evidenced a steep enhancement of the Mn²⁺ concentration upon increasing antimony doping level, explained by a charge compensation mechanism, between the Sb³⁺ ions substituting Pb²⁺ at the A-sites and the Mn²⁺ ions, localized at the B-sites. The incorporation of Sb³⁺ at the A-site of the PZT lattice is also supported by the variation of the lattice parameters, determined by X-ray Diffraction, with the increasing Sb concentration. The investigation of the dielectric, electromechanical and ferroelectric properties evidenced a hard piezoelectric behavior, mainly attributed to the presence of large sized Mn²⁺ ions, localized at B-sites. Our results prove that the piezoelectric hard/soft response is decisively influenced by the interplay between multiple valence states and locations of the co-dopants, on one hand, and the charge compensation mechanisms, on the other hand. This provides indirect information about the location of some co-dopants which can substitute for both cationic sites in the PZT based ceramics.