Achieving high piezoelectric performances with enhanced domain-wall contributions in <001>-textured Sm-modified PMN-29PT ceramics

1% Sm substituted PMN-29PT ([Sm_0.01Pb_0.985][(Mg_1/3Nb_2/3)_0.71Ti_0.29]O₃) textured ceramics with a Lotgering factor of up to 80 % were successfully prepared. The dielectric, ferroelectric and piezoelectric properties have been investigated in detail for both textured and non-textured ceramics. The heterogeneous templates are found to be critical for the change in relaxor behaviors, leading to the reduced T_f, T_m, ε_max and P_r in textured ceramics. The textured ceramics show an enhanced d₃₃ of 810 pC/N, about 1.6 times greater than their randomly oriented ceramic counterparts. The domain structures and their responses to applied electric fields have been studied using piezoresponse force microscopy, signifying the enhanced extrinsic contributions by the increased domain wall densities and dynamics. The improved dielectric and piezoelectric properties are discussed and explained from the view point of extrinsic contributions in textured ceramics. The results demonstrate that the textured Sm-PMN-PT piezoelectric ceramics could be promising high performance piezoelectrics with low cost.     

Structural and piezoelectric properties of <001> textured PZT‐PZNN piezoelectric ceramics

Rhombohedral 0.69Pb(Zr_0.47Ti_0.53)‐0.31Pb(Zn_0.6Ni_0.4)NbO₃ (PZT‐PZNN) ceramics were textured using 10.0 vol. % BaTiO₃ (BT) platelets along the <001> direction at 950°C with a high Lotgering factor of 95.3%. BT platelets did not react with the PZT‐PZNN ceramics, and the textured PZT‐PZNN ceramic had a tetragonal structure. The PZT‐PZNN ceramics exhibited a strain of 0.174% with a piezoelectric strain constant (d*₃₃) of 580 pC/N at 3.0 kV/mm. The textured PZT‐PZNN ceramic showed an increased strain of 0.276% and d*₃₃ of 920 pC/N at 3.0 kV/mm, which can be explained by the domain rotation. However, the d₃₃ values of the textured specimens are smaller than those of the untextured specimens because of the small remanent polarization and relative dielectric constant of BT platelets. The textured PZT‐PZNN ceramic synthesized in this work can be used for piezoelectric multilayer actuators because of its large strain and low sintering temperature.     

High and temperature-insensitive piezoelectric performance in the lead-free Sm-doped BiFeO3–BaTiO3 ceramics with high Curie temperature

Large sensor piezoelectric constant (d₃₃ = 334 pC/N) and superior actuator piezoelectric constant (d₃₃* = 552 pm/V) as well as a high Curie temperature (T_C = 454 °C) were obtained simultaneously in the lead-free 0.67Bi_1.03FeO₃-0.33Ba_1-xSm_xTiO₃ ceramics. Such an excellent and temperature-insensitive piezoelectric performance with only 10% temperature variation of piezoelectric strain at the range of 25–125 °C is highly desirable for real applications. The structural origin of the enhanced piezoelectric performance is mainly attributed to the morphotropic phase boundary and the highest known tetragonality (c_T/a_T = 1.02) in such materials. Transmission electron microscopy and electro-mechanical phenomenological theory demonstrate that the superior d₃₃ and d₃₃* are associated with the hybrids nanodomains (60–90 nm) and flattened thermodynamic energy profile owing to the local structure heterogeneity. These results are superior as the piezoelectric properties are temperature-independent and the material has large d₃₃*, and high T_C compared to other lead-free piezoelectric ceramics.     

Determining the effects of BaTiO3 template alignment on template grain growth of Pb(Mg1/3Nb2/3)O3 –PbTiO3 and effects on piezoelectric properties

Crystallographic texturing of ferroelectric ceramics is an established method of inducing single crystal-like properties in a ceramic material via epitaxial grain growth according to the template used, otherwise known as Templated Grain Growth (TGG). The piezoelectric enhancement is dependent on the degree of TGG throughout the ceramic, which is closely linked to the tape casting parameters and sintering conditions. Pb(Mg1/3Nb2/3)O₃-PbTiO₃ (PMN-PT) perovskite ferroelectrics with morphotropic phase boundary compositions using 3 vol% BaTiO₃ templates were used for analysis. The blade gap and template size have the greatest impact on the overall grain alignment. The varying degrees of template alignment is related to the different enhancements of TGG and the correlating piezoelectric d₃₃ and d*₃₃. The highest piezoelectric property was demonstrated in PMN-31PT with Lotgering factor of 93% where d₃₃ = 1020 pC/N and d*₃₃ = 1420 pm/V were achieved.     

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.     

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.     

Low electric field induced large electromechanical properties of BiFeO3-BaTiO3-based ceramics via phase composition modulation

The development of high-temperature lead-free piezoelectric ceramics with excellent electromechanical properties under low field remains a key challenge. A series of 0.995(xBiFeO₃-(1-x)BaTiO₃)-0.005Bi(Zn_0.5Hf_0.5)O₃ ceramics were designed via modulating phase composition. The excellent electromechanical properties of d₃₃* = 511 pm/V (45 kV/cm) at room temperature and S = 0.476 % (d₃₃* = 1190 pm/V, 40 kV/cm) at 120 ℃ were achieved in the x = 0.67 ceramic owing to the synergistic contribution of phase composition and domain evolution. The XRD results verify that the x = 0.67 ceramic is dominated by the pseudocubic phase. The PFM results in the x = 0.67 and 0.71 ceramics confirm that the domain structures consist of nanodomains with strong and weak piezoelectric responses. More importantly, the temperature and voltage-dependent domain evolution testify the nanodomains are easier to switch in the x = 0.67 ceramic. This work provides a strategy to optimize the electromechanical performance at the low field and a deeper understanding of BF-BT-based piezoceramics.     

Achieving both high electromechanical properties and temperature stability in textured PMN-PT ceramics

Textured piezoelectric ceramics, such as textured Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃ (PMN-PT) ceramics, have attracted considerable attention from both academia and industry, as they possess crystal-like piezoelectric properties, high composition homogeneity, and low manufacturing cost. However, the main difficulty with the textured piezoelectric ceramics is the presence of BaTiO₃ (BT) templates, which greatly reduces their piezoelectricity and phase transition temperature. Thus, it is highly recommended to fabricate textured piezoelectric ceramics using as few templates as possible. Here, we successfully fabricated high-quality <001>-textured PMN-28PT ceramics (texturing degree of 99%) by using an extremely small amount of BT templates (1 vol.%) with the help of CuO/B₂O₃ sintering aids. The textured PMN-28PT ceramic exhibits 80% piezoelectric coefficient (d₃₃ ∼ 1200 pC/N), 96% electromechanical coefficient (k₃₃ ∼ 88%) and the same temperature stability (T_rt ∼ 100, T_c ∼ 150°C) when compared to its single crystal counterpart. In addition, by using an alternating current electric field poling (AC-poling), the piezoelectric coefficient d₃₃ and dielectric permittivity ε₃₃ of the textured PMN-28PT ceramics were further enhanced around 5–8%. It is believed that the advantages of high electromechanical properties, low cost, and easy mass production of textured PMN-28PT ceramic will make it a promising candidate for advanced electromechanical devices.     

Textured CaBi4Ti4O15 ceramics with large piezoelectricity,excellent thermal stability and high resistivity

The bismuth layer-structured ferroelectrics (BLSF) are promising high-temperature piezoelectric materials, in which large piezoelectricity, good thermal stability and high electrical resistivity are desired. Here highly textured CaBi₄Ti₄O₁₅ BLSF ceramics with orientation factor of 82% have been fabricated by spark plasma sintering technique. The piezoelectric coefficient d₃₃ is significantly enhanced by 250%, from 7.2 pC/N for the texture-less sample to 25.3 pC/N for the textured one, accompanied by a high Curie temperature T_C= 788 °C. The variation of d₃₃ is below 5% in the temperature range of 25–500 °C, showing excellent thermal stability. The textured sample exhibits high electrical resistivity ρ = 2.1 × 10¹¹ Ω·cm, an order of magnitude larger than that of the texture-less sample. At the temperature as high as 500 °C, the textured sample still maintains excellent electrical properties of d₃₃ = 24.2 pC/N, tanδ = 9.9% and ρ = 2.7 × 10⁶ Ω·cm, suggesting that the textured CaBi₄Ti₄O₁₅ ceramics could be a potential candidate for high-temperature piezoelectric sensor or detector applications.     

Textured (K0.5Na0.5)NbO3 ceramics prepared by screen-printing multilayer grain growth technique

The screen-printing multilayer grain growth (MLGG) technique is successfully applied to alkaline niobate lead-free piezoelectric ceramics. Highly textured (K_0.5Na_0.5)NbO₃ (KNN) ceramics with 〈0 0 1〉 orientation (f = 93%) were fabricated by MLGG technique with plate-like NaNbO₃ templates. The influence of sintering temperature on grain orientation and microstructure was studied. The textured KNN ceramics showed very high piezoelectric constant d₃₃ = 133 pC/N, and high electromechanical coupling factor k_p = 0.54. These properties were superior to those of conventional randomly oriented ceramics, and reach the level of those of textured KNN ceramic prepared by tape-casting technique. Compared with other grain orientation techniques, screen-printing is a simple, inexpensive and effective method to fabricate grain oriented lead-free piezoelectric ceramics.     

Sm2O3 and MnO2 codoped PMN-PZT ceramics with both high mechanical quality factor and piezoelectric properties

For lead-based ceramics used in high-power devices, it is essential that they possess both a high mechanical quality factor (Q_m) and a large piezoelectric coefficient (d₃₃). Unfortunately, Q_m is inversely proportional to d₃₃ for piezoelectric ceramics, which the limits their actual application. If suitable acceptor and donor dopants can be added in piezoelectric ceramics, it is rational to achieve high Q_m and large d₃₃ simultaneously. Herein, we tried to achieve both a high mechanical quality factor and large piezoelectric activity in 0.47 pb(Mg_1/2Nb_2/3)O₃-0.18PbZrO₃-0.35PbTiO₃ (PMN-PZT) ceramics via Sm₂O₃ and MnO₂ co-doing. A range of xMn-2Sm-PMN-PZT ceramics were fabricated by the traditional sintering method. An optimal performance was attained in 4Mn-2Sm-PMN-PZT ceramics with Q_m = 1720, d₃₃ = 450 pC/N, ε = 2720 and k_p = 0.54. The high Q_m is related to the presence of defect dipoles as a result of MnO₂ doping and the large piezoelectric activity is due to the doping of Sm₂O₃.     

Effect of particle grading on the properties of photosensitive slurry and BaTiO3 piezoelectric ceramic via digital light processing 3D printing

To improve the density and piezoelectric constant of BaTiO₃ ceramics prepared by Digital Light Processing 3D printing, the properties of photosensitive slurry were investigated from the perspective of particle grading, and the nitrogen-air two-step debinding and sintering process on the relative density and electrical properties were explored. It was found that as the mass ratio of coarse particles increased, the viscosity, shear stress and cure depth of the slurry decreased. When the mass ratio of fine and coarse particles was 2:8 and sintered at 1350 °C, the ceramic had better performance, with relative density reaching 95.39 ± 0.63 %. The piezoelectric constant d₃₃ was 215 ± 13 pC/N, 29.52 % higher than the single-peak powder. The relative permittivity (ε_r) and polarization (P_r) were 978 and 16.656 μC/cm². Finally, BaTiO₃ ceramics with Triply Periodic Minimal Surface structures were prepared as piezoelectric sensors, which had the highest output voltage at the same displacement when the mass ratio was 2:8.     

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.     

Achieving large piezoelectric response and ultrahigh electrostriction in [001] textured BiScO3-PbTiO3 high-temperature piezoelectric ceramics

[001] textured 0.40BiScO₃-0.60PbTiO₃-0.125 mol%Nb⁵⁺ (BS-60PT-0.125Nb) high-temperature piezoelectric ceramics were synthesized using templated grain growth process. A high texture degree F₀₀₁ of 99% was obtained using 2 vol% BaTiO₃ (BT) templates. The piezoelectric charge constant d₃₃ and the unipolar strain under 40 kV cm⁻¹ at room temperature for the textured ceramics are 646 pC N⁻¹ and 0.36%, respectively, which is over two times as those for untextured ceramics (∼243 pC N⁻¹ and 0.17%). The electrostriction Q₃₃ value of the textured sample remarkably increased from 0.034 m⁴ C⁻² to 0.068 m⁴ C⁻² under 30 kV cm⁻¹, showing a twice higher than untextured. Compared with random ceramics, the improvement piezoelectric response of the textured ceramics is primarily attributed to the increase of the dielectric constant ε_r and electrostriction coefficient Q₃₃ along [001] orientation, which is originating from the anisotropy of piezoelectricity. The BS-60PT-0.125Nb textured ceramics have large piezoelectric response and ultrahigh electrostriction with high temperature stability (high depolarization temperature T_d of ∼360°C and high Curie temperature T_c of 421°C), showing great potential for the piezoelectric applications at high temperatures.     

Comparison of multi-valent manganese oxides (Mn4+, Mn3+, and Mn2+) doping in BiFeO3-BaTiO3 piezoelectric ceramics

Different manganese oxides-doping effects were compared in piezoceramic BiFeO₃-BaTiO₃ system. 0.67Bi_1.05(Fe_0.99Mn^x_0.01)O₃-0.33BaTiO₃ (valence state x = 4+, 3+, and 2+) ceramics were prepared via a solid-state reaction process followed by furnace-cooling (FC) or water-quenching (WQ) process. For the FC ceramics, the direct piezoelectric sensor coefficient (d₃₃) was almost independent of valence state of doped Mn, while d₃₃ depended on the fraction of Fe³⁺/Fe²⁺ in WQ ceramics. The d₃₃ value was highest for the donor Mn⁴⁺-doped ceramic, among the FC ceramics, with 175 pC/N. However, acceptor-doping with Mn²⁺ prevented the transition of Fe ion valence state from 3+ to 2+ in the WQ ceramics, the Mn²⁺-doped WQ ceramic showed the largest d₃₃ of 313 pC/N and converse piezoelectric actuator coefficient, d₃₃^* of 352 pm/V, with high Curie phase transition temperature (482 °C).     

Enhanced piezoelectric properties in BF-BT based lead-free ferroelectric ceramics for high-temperature devices

Due to the high Curie temperature (T_C), BiFeO₃–BaTiO₃ (BF-BT) ceramics have been broadly investigated in high-temperature piezoelectric devices. The piezoelectric constant is one of the most significant factors in determining the sensitivity and reliability of piezoelectric functional components. However, the poor piezoelectric constant (d₃₃) of BF-BT ceramic has prevented the practical application of the material. In this work, we innovatively introduce the 0.93Bi_0.5Na_0.5TiO₃-0.07BaTiO₃ (0.93NBT-0.07BT) component to 0.7BF-0.3BT ceramic, to build a morphotropic phase boundary (MPB) for enhancing d₃₃. The XRD analysis shows that the (0.7BF-0.3BT)-x(0.93NBT-0.07BT) ceramics are still in the MPB region with R–PC phases coexistence, and exhibits a homogeneous solid solution. Moreover, the introduction of 0.93NBT-0.07BT ceramic suppresses the generation of defects and facilitates grain growth, thus enhancing piezoelectric property. In consequence, an optimum piezoelectricity d₃₃ = 213 pC/N along with T_c～450 °C was obtained in (0.7BF-0.3BT)-0.01(0.93NBT-0.07BT). This research provides a new idea for the application of BF-BT ceramics in high-temperature piezoelectric devices.     

A comparative study of direct and indirect evaluation of piezoelectric properties of electrophoreticaly deposited (Ba,Ca) (Zr,Ti)O3 lead-free piezoceramics

The development and optimisation of piezoceramics are targeted usually to enhance their piezoelectric properties evaluated by both the direct or indirect measurement methods. The presented work aims to elaborate on the correlation of one direct (Berlincourt) and two indirect (convert and field-dependent) piezoelectric measurement methods on various material states. The role of the ceramic powder treatment by ball milling and electrophoretic deposition (EPD) technique on the determined electric properties as well as basic physical and mechanical properties of (Ba_0.85Ca_0.15) (Zr_0.1Ti_0.9)O₃ ceramics (BCZT) was investigated. It was found that the EPD technologically supported by milling allows obtaining thick and dense deposits (>2 mm). After sintering, the BCZT ceramics with a relative density of >95%, hardness in the range of 2.3–2.9 GPa and piezoelectric coefficients of d₃₃* = 940 pm/V, d_33(E=0) = 427 pm/V and d₃₃ = 364 pC/N can be achieved. Reported results also suggest that indirect (field-dependent) and direct (Berlincourt) measurements of the piezoelectric coefficients can be comparable at optimal poling conditions.     

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.     

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.     

3D printing of porous scaffolds BaTiO3 piezoelectric ceramics and regulation of their mechanical and electrical properties

A series of porous scaffolds of piezoelectric ceramic barium titanate (BaTiO₃) were successfully fabricated by Digital Light Processing (DLP) 3D printing technology in this work. To obtain a high-precision and high-purity sample, the debinding sintering profile was explored and the optimal parameters were determined as 1425 °C for 2h. With the increase of scaffolds porosity from 10% to 90%, the compressive strength and piezoelectric coefficient (d₃₃) decreased gradually. The empirical formulas about the mechanical and piezoelectric properties were obtained by adjusting BaTiO₃ ceramics with different porosity. In addition, the distribution of potential and stress under 100 MPa pressure were studied by the finite element method (FEM).