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.     

Influence of bimodal particle distribution on material properties of BaTiO3 fabricated by paste extrusion 3D printing

Barium titanate (BaTiO₃) is a lead-free piezoelectric ceramic widely used in sensors and actuators applications. However, there are many manufacturing challenges to process BaTiO₃ due to the brittle nature of ceramics. Most current sensors based on piezoelectricity are limited to mold shapes or flat 2D structures, which narrow their applications. Paste extrusion (PE) 3D printing technique allows the fabrication of complex geometry ceramics with less design limitations. However, the piezoelectric property of 3D printed ceramics is typically lower than those fabricated using traditional means due to lower density. Herein, a study to evaluate the influence of bimodal particle distribution on improving density and piezoelectricity of BaTiO₃ ceramics fabricated using PE 3D printing is presented. 3D printed and compression pressed samples under the same mixing ratios were compared. The highest packing density was obtained using 50-50% vol. fraction of bimodal particles for both types of samples. A predictive model for packing density was validated by experimental results. The highest piezoelectric coefficient of 350 pC/N was obtained using 50-50% vol. bimodal particle distribution. This piezoelectric coefficient is 40% higher than the monodispersed sample using 100 nm particles with a piezoelectric coefficient of 250 pC/N.     

Piezoelectric calcium/manganese-doped barium titanate nanofibers with improved osteogenic activity

The piezoelectric nature of natural bone tissue makes the use of piezoelectric biomaterials in promoting bone regeneration to be a feasible and attractive strategy. Barium titanate (BaTiO₃) is well-known for its high piezoelectricity and widely studied as bone repairing bioceramic, but its lacking of bioactive ions may compromise its contribution to osteogenesis. Calcium is the richest metallic element in bone mineral, and manganese is an important doping element for hydroxyapatite, therein, Ca²⁺ and Mn⁴⁺ were individually or co-doped into BaTiO₃ nanofibers via sol-gel/electrospinning/calcination technique in this study. Compared to pure BaTiO₃ nanofibers, though the piezoelectric coefficient (d₃₃) of Ca²⁺ and/or Mn⁴⁺-doped BaTiO₃ nanofibers decreased with increase in ion doping amount, it could maintain approx. 0.9–3.7 pC/N and comparable to that of native bone (0.7–2.3 pC/N) at an optimized content. Under the synergistic effect of the released bioactive ions and the material piezoelectricity, the BaTiO₃ nanofibers co-doped with Mn⁴⁺ (2 mol%) and Ca²⁺ (10 mol%) (i.e., the sample 2Mn10Ca-BT) achieved the strongest capacity in enhancing the osteogenic differentiation of bone marrow mesenchymal stromal cells (BMSCs), while showing no cytotoxicity. In summary, bioactive ions-doped BaTiO₃ nanofibers are promising scaffolds for bone tissue engineering, thanks to their acceptable biocompatibility, appropriate piezoelectricity, and improved osteogenic activity.     

Crystal Structure and Electrical Properties of Lead‐Free (1 − x)BaTiO3–x(Bi1/2A1/2)TiO3 (A = Ag,Li, Na,K, Rb,Cs) Ceramics

Ceramics of solid solutions (1  ?  x)BaTiO₃–x(Bi_1/2A_1/2)TiO₃ (A = Ag, Li, Na, K, Rb, Cs, x ≤ 0.20) were prepared and their crystal structures, dielectric, ferroelectric, and piezoelectric properties were investigated. It was found that (Bi_1/2A_1/2)TiO₃‐type doping compounds broadened the temperature range of the tetragonal phase in BaTiO₃ and all the compositions examined displayed a tetragonal structure at room temperature. The Curie temperature (T_C) was observed to increase with respect to pure BaTiO₃ to the range 140°C–210°C through solid solution. Remanent polarization (P_r) tended to decrease with increased content of doping compound, whereas the coercive field (E_C) rose and piezoelectric coefficient (d₃₃) fell. The highest d₃₃ value in the solid solutions was observed in 0.97BaTiO₃–0.03(Bi_1/2Ag_1/2)TiO₃ at 90 pC/N.     

Synthesis and piezoelectric properties of Li-doped BaTiO3 by a solvothermal approach

Li-doped BaTiO₃ particles with the Li⁺ mole fraction, x, of 0–0.06 were synthesized by a solvothermal approach at 200 °C. The products consisted of nanoparticles of 50–100 nm in diameter. The sinterability and piezoelectric property of Li-doped BaTiO₃ were improved by doping with Li ion, i.e., the Li-doped BaTiO₃ samples could be sintered to almost full theoretical density (>95%) at a low temperature such as 1100 °C, and the highest piezoelectric constant, d₃₃ (260 pC/N) and electromechanical coupling factor, k_p (43.7%) could be realized at x value of 0.03. The Curie temperatures of all samples were around 130 °C, and did not change very much depending on the amount of Li-doping.     

Grain Size Effects on Piezoelectric Properties and Domain Structure of BaTiO3 Ceramics Prepared by Two‐Step Sintering

A series of highly dense barium titanate (BaTiO₃) ceramics with the average grain size (GS) from 0.29 to 8.61 μm are successfully prepared by two‐step sintering, and the GS effect on piezoelectric coefficient (d₃₃) is systematically discussed in this work. It is found that when GS above 1 μm, d₃₃ can be enhanced with decreasing GS, reaching a maximum value of 519 pC/N around 1 μm due to the high activity of domain wall mobility. Subsequently, d₃₃ rapidly drops with a further decrease in GS owing to the reduced domain density. The results suggest that it is possible to prepare high‐performance BaTiO₃ ceramics by controlling the GS and domain configuration properly, which brings great revitalization to the BaTiO₃‐based piezoceramics.     

Large electric‐field‐induced strain and enhanced piezoelectric constant in CuO‐modified BiFeO3‐BaTiO3 ceramics

In this work, we fabricated the (1‐x)BiFeO₃‐xBaTiO₃+y‰ mol CuO ceramics by the modified thermal quenching technique. The pure perovskite phase was formed and a morphotropic phase boundary (MPB) was observed in the ceramics with x = 0.30‐0.33. The addition of CuO can significantly enhance the density of the BiFeO₃‐BaTiO₃ material. Importantly, an enhanced piezoelectric constant (d₃₃=165 pC/N), a large electric‐field‐induced strain (?S = 0.54%: peak to peak strain) and a large piezoelectric actuator constant (d₃₃*=449 pm/V) together with a high Curie temperature (T_C) of 503°C were observed in the ceramics with x = 0.30 and y = 5. As a result, the enhanced piezoelectricity and large electric‐field‐induced strain could significantly stimulate further researches in BFO‐based ceramics.     

Phase evolution and <110>-orientation mechanism in RTGG-processed BaTiO3 ceramics with electrical properties

The <110>-oriented BaTiO₃ ceramics were fabricated using BaCO₃ matrix and H_1.08Ti_1.73O₄.nH₂O (HTO) template particles, and the mechanism of BaTiO₃ phase formation was investigated. The dielectric, ferroelectric, and piezoelectric properties were also investigated. The transformation of the HTO phase into the TiO₂ bronze or TiO₂ (B) phase was observed at 600°C, where the BaTiO₃ nucleation was accompanied by the formation of a Ba₂TiO₄ phase. The TiO₂ phase reacted with the Ba₂TiO₄ phase at 800°C to give a BaTiO₃ phase, whereas its reaction with the BaTiO₃ resulted in the formation of BaTi₂O₅ phase that got decomposed into BaTiO₃ and Ba₆Ti₁₇O₄₀ phase at sintering temperature ≥1300°C. Sintering with samples’ embedding in BaTiO₃ powders prevented the formation of the Ba₆Ti₁₇O₄₀ secondary phase. The crystallographic orientation along the <110> direction (F₁₁₀) was developed by the epitaxial grain growth mechanism. In addition to the contribution of the grain-size increment for enhancing the F₁₁₀, the preservation of the platelike structure was also found to have a significant impact. The ceramics prepared by the embedded sintering (grain size ≈12.4 µm and F₁₁₀ = 83%) exhibited the room-temperature dielectric constant of 1708 and piezoelectric strain constant of 445 pm/V, which are higher than those of the BaTiO₃ ceramics with randomly oriented grains.     

Sintering of ferrite-BaTiO3 bulk particulate composites

Particulate magnetoelectric ceramic composites (PMCC) have received much attention since the last decade. These composites have many technological applications and are usually composed by magnetostrictive and piezoelectric phases. Cobalt-based spinel ferrites are among the most studied magnetostrictive phases for ferrite-based PMCCs and BaTiO₃ is an interesting choice for the piezoelectric phase because it is a lead-free ceramic, unlike the traditional PZT. In this work, cobalt ferrite (FCO) and Ni–Co ferrite (FNICO) were produced by the ceramic method and mixed to BaTiO₃ (TB) in order to further obtain sintered ferrite-BaTiO₃ particulate ceramic composites with a composition of 15 mol% ferrite – 85 mol% BaTiO₃. The ferrites, the BaTiO₃, and the ferrite-BaTiO₃ mixtures were analyzed by dilatometry, thermogravimetry (TG), and calorimetry (DSC) in temperatures up to 1300–1400 °C, with the aim to analyze the sintering behavior and the interactions between both ferrites and the BaTiO₃ during sintering. Sintered TB-FNICO and TB-FCO composite samples were also produced and they were analyzed by scanning electron microscopy (SEM) and X-ray diffractometry (XRD). The dilatometry results evidenced that the densification of the ferrite-BaTiO₃ samples is impaired, when compared to the pure ferrite and BaTiO₃ samples. The DSC/TG results evidenced the occurrence of reactions between the ferrites and the BaTiO₃ when they are co-sintered in air or argon atmospheres. The XRD patterns of the sintered composite samples did not exhibit diffraction peaks attributed to a third phase, whilst the punctual EDS analysis showed evidence of diffusion between the ferrite and BaTiO₃ particles.     

Highly compressible ceramic/polymer aerogel-based piezoelectric nanogenerators with enhanced mechanical energy harvesting property

Ceramic piezoelectric materials have orders of magnitude higher piezoelectric coefficients compared to polymers. However, their brittleness precludes imposition of large strains in mechanical energy harvesting applications. We report here that ice templating affords low bulk modulus lead-free aerogel piezoelectric nanogenerators (PENG) with unprecedented combination of flexibility and high piezoelectric response (voltage and power density). A modified ice templating protocol was used to fabricate piezoelectric nanocomposites of surface modified BaTiO₃ (BTO) nanoparticles in crosslinked polyethylene imine. This protocol allowed incorporating a significantly high fraction of BTO particles (up to 83 wt %) in the aerogel, while retaining remarkably high compressibility and elastic recovery up to 80% strain. The output voltage, at an applied compressive force of 20 N (100 kPa), increased with BTO loading and a maximum output voltage of 11.6 V and power density of 7.22 μW/cm² (49.79 μW/cm³) was obtained for PENG aerogels containing 83 wt% BTO, which is orders of magnitude higher than previously reported values for foam-based piezoelectric energy harvesters. The BTO/PEI PENGs also showed cyclic stability over 900 cycles of deformation. PENGs with higher porosity showed better elastic recovery and piezoelectric properties than lower porosity and higher BTO content aerogels. To the best of our knowledge, this is the first report to demonstrate the piezoelectric properties of high ceramic content aerogels having very high compressibility and elastic recovery.     

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.     

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.     

3D printing orientation controlled PMN-PT piezoelectric ceramics

Piezoelectric textured ceramics have drawn increasing research and industry interests by balancing the production cost and material performances. A new approach to realize the texture in piezoelectric ceramics is developed based on 3D printing stereolithography (SL) technique and successfully applied in the preparation of < 001 > -textured 0.71(Sm_0.01Pb_0.985)(Mg_1/3Nb_2/3)O₃-0.29(Sm_0.01Pb_0.985)TiO₃ (1 %Sm-PMN-29PT) ceramics in this work. As a critical process in texture ceramic fabrication, the alignment of BaTiO₃ templates along the horizontal direction is achieved by the shear force produced from the relative motion between the resin container and the blade during SL. The textured ceramics with obvious grain orientation features are successfully obtained. The enhanced piezoelectric properties of d₃₃ ≈ 652 pC N^?1 and d₃₃* ≈ 800 pm V^?1 are achieved in the 3D printed textured ceramic, which are about 60 % and 40 %, respectively, higher than their non-textured counterparts. Moreover, the textured sample shows a significant improvement on thermal stability of d₃₃*_T, which varies by less than ± 6 % from RT to 110 °C. Furthermore, the introduction of 3D printing into the synthesis of textured piezoelectric ceramics shows great advantages over the traditional tape-casting method. This work is expected to provide a promising way for the future design of textured piezoelectric functional materials.     

Electrocaloric behavior and piezoelectric effect in relaxor NaNbO3-based ceramics

We firstly reported the electrocaloric properties in relaxor (1−x−y)NaNbO₃–yBaTiO₃–xCaZrO₃ ceramics, and high electrocaloric effect (∆T ~0.451 K and∣∆T/∆E∣~0.282 Km/MV) can be realized in the ceramics (x = 0.04 and y = 0.10) under low temperature and low electric field. Relaxor behavior of NaNbO₃ ceramics can be found by doping both BaTiO₃ and CaZrO₃. In addition, optimized piezoelectric effects (d₃₃ ~235 pC/N and d₃₃* ~230 pm/V) can be observed in the ceramics (x = 0.04 and y = 0.10) due to the involved morphotropic phase boundary (MPB). Excellent piezoelectric effect (ie, d₃₃~330 pm/V at 41°C, and d₃₃*~332 pm/V at 60°C) can be found because of the characteristics of MPB. Good temperature reliability of piezoelectric effect can be shown because of both MPB and relaxor behavior. We believe that the ceramics with high electrocaloric effect and good piezoelectric effect can be considered as one of the most promising lead-free materials for piezoelectric devices.     

BaTiO3 nanocubes-Gelatin composites for piezoelectric harvesting: Modeling and experimental study

Flexible composites containing BaTiO₃ nanoparticles into Gelatin bio-polymer matrix were designed and investigated. Following the idea that the electric field concentration in corners/edges at the interfaces between dissimilar materials give rise to enhanced effective permittivity in composites, cuboid-like BaTiO₃ nanoparticles have been employed as nanofillers into Gelatin matrix by using an inexpensive solution-based processing method. As predicted by finite element method simulations developed for cubic-like inclusions into a homogeneous polymer matrix, the experimental permittivity of xBT-(1-x)Gelatin composites increases when increasing the high-permittivity filler addition. For the composition x = 40 wt% (corresponding to 12 vol% BaTiO₃ addition), permittivity reaches ε_r ～15.7 with respect to ε_r ～9.8 of pure Gelatine (measured at 10⁵ Hz), while the average piezoelectric coefficient d₃₃ as determined by piezoelectric force microscopy shows a remarkable increase up to 21 pm/V in composites with x = 40 wt%, in comparison to ～7 pm/V in pure Gelatin. By using the experimentally determined material constants, the simulated piezoelectric voltage output vs. time has shown a similar increase (about a doubling of its amplitude) of the harvesting signal in the composite with x = 40 wt% BT, with respect to one of the polymer matrix, thus demonstrating the beneficial role of embedding BT nanoparticles into the biopolymer for increasing the mechanical harvesting response.     

The dielectric properties of BaTiO3 based ceramics co-doped with Bi/Mn

BaTiO₃ based ceramics (with some additives such as ZrO₂, SnO₂, etc.) were prepared by solid state reaction. Mn²⁺ or Mn³⁺ as an acceptor substituting for Ti⁴⁺ in B site and Bi³⁺ as a donor substituting for Ba²⁺ in A site were co-doped in BaTiO₃ based ceramics. The dielectric properties of BaTiO₃ based ceramics co-doped with Bi/Mn were investigated. The results show that the dielectric properties of BaTiO₃ based ceramics co-doped with Bi/Mn are affected by the mole ratio of donor and acceptor (Bi/Mn). When the mole ratio of donor and acceptor is high, dielectric dispersion behavior was observed and the dielectric constant decrease and remnant polarization, coercive field and piezoelectric constant will varied. When Bi varied from 1.0% to 2.0 mol% (Mn = 0.8 mol%), remnant polarization from 10.35 to 2.25 μC/cm², coercive field from 4 to 2.75 kV/cm, and piezoelectric constant d₃₃ from 137 to 36 pC/N respectively.     

Piezoelectric properties of mechanochemically processed 0.67BiFeO3-0.33BaTiO3 ceramics

Solid solutions of BiFeO₃ and BaTiO₃ are promising lead-free piezoelectric materials, especially around the morphotropic phase boundary at 0.67BiFeO₃-0.33BaTiO₃. Still, these materials are challenged by phase instability and limited understanding of the processing-properties relationship. Here, we investigate mechanochemical activation and the use of BaTiO₃ as seed particles for the 0.67BiFeO₃-0.33BaTiO₃ phase. Contrary to expectations from seeding in lead-based perovskites, the BaTiO₃ seeds do not promote the 0.67BiFeO₃-0.33BaTiO₃ perovskite phase neither during the mechanochemical activation nor the subsequent sintering, but cause an inhomogeneous structure with remnant BaTiO₃. This results in ceramics with weaker low-field piezoelectric response than that of the unseeded route, but with higher field-induced strain, even up to 150 °C. Both routes produce ceramics of high density and without significant secondary phases visible by X-ray diffraction. This demonstrates the advantage of mechanochemical activation and the possibility to tailor the piezoelectric response of 0.67BiFeO₃-0.33BaTiO₃ through the processing route.     

Notable grain-size dependence of converse piezoelectric effect in BaTiO3 ceramics

Converse piezoelectric effect is of critical importance to device applications like actuators, but no systematical investigation concerning the influence of microstructure on it has been reported for BaTiO₃ ceramics so far. Piezoelectric and ferroelectric properties were inclusively investigated for a group of BaTiO₃ ceramics that are fabricated through solid-state reaction route and show various average grain sizes in this study. It was found that the piezoelectric properties of these BaTiO₃ ceramics display significant grain-size dependences. The direct piezoelectric coefficient d₃₃ increases with decreasing the average grain size (GS) from 170 pC/N at 40 μm, reaches a maximum value of 413 pC/N at 1.2 μm, and then decreases with a further reduction of GS. Converse piezoelectric effect was characterized by measurement of unipolar strain versus electric field (S–E) curve, and the converse piezoelectric coefficient d₃₃*(E) was quantitatively calculated from the slope of S–E curve at relatively large E. Interestingly, d₃₃*(E) is nearly twice as large as d₃₃ and shows a quite similar trend of change with GS to d₃₃. It increases largely from 350 pm/V to 870 pm/V when reducing the GS value from 40 μm to 1.2 μm, and then decreases to 480 pm/V with the further GS reduction to 0.7 μm. Meanwhile, the remanent polarization P_r shows an increase with the decreasing of GS, reaches a maximum at 3.3 μm, and then decreases with the further GS reduction. Domain structure is considered to play an essential role in determining the notable grain-size dependence of converse piezoelectric effect.     

Microstructure and electrical properties of Er-doped 0.67 Pb(Mg1/3Nb2/3)O3-0.33PbTiO3 ceramics with BaTiO3 templates

In this study, [001]-oriented Er-doped 0.67 Pb(Mg_1/3Nb_2/3)O₃-0.33PbTiO₃ (0.67PMN-0.33 PT) textured ceramics with different BaTiO₃ (BT) template concentrations were explored. The samples were prepared by tape-casting. Er³⁺ was added to modify the electrical properties of the polycrystalline ceramics, and the BT template was used to improve the texture of polycrystalline ceramics. The 0.67PMN-0.33 PT textured ceramics contained coexisting rhombohedral and tetragonal phases. The ceramics became increasingly textured as the sintering temperature increased up to 1250 °C. The piezoelectric coefficient of 0.67PMN-0.33 PT with 5 wt% BT was 634 pC/N, which is 1.2 times than that of randomly oriented 0.67PMN-0.33 PT. The strain of the ceramic with 5 wt% BT increased by 12.5% relative to a random control specimen. Analysis of the electrical properties and microstructure suggested that the enhancement of the piezoelectric coefficient and strain may be caused by the addition of Er³⁺ and the BT template. First, the directional growth of grains along the template affected the change-of-phase distribution of the system and formed a more adaptive phase. Second, Er³⁺ was substitutionally doped on the A-site of the perovskite to form local heterostructures. Finally, the relaxation components of the templates and Er³⁺ changed in the solid solution with the matrix. The solid solution of the BT templates and Er-doped-matrix powder changed the relaxation degree, which affected the interactions at the polar nanoregions and increased the piezoelectric coefficient of the ceramics.     

Low sintering temperature for lead-free BiFeO3-BaTiO3 ceramics with high piezoelectric performance

Through modification of the heat-treatment process using a higher heating rate and a lower binder burnout temperature, the piezoelectric performance of water-quenched 0.67Bi_1.05FeO₃-0.33BaTiO₃ (BF33BT) lead-free piezoelectric ceramics was improved. The observed physical properties of BF33BT ceramics were very sensitive to the process temperatures. The sintering temperature (T_S) was changed within a narrow temperature range, and its effects were investigated. The largest rhombohedral distortion (90°-α_R = 0.14°) and tetragonality (c_T/a_T = 1.022) were observed for the ceramic sintered at 980°C, and its Curie temperature was 476°C. This ceramic showed good piezoelectric properties and large grains; the piezoelectric sensor charge coefficient (d₃₃) was 352 pC/N, and the piezoelectric actuator charge coefficient () was 270 pm/V. The high piezoelectric performance and low T_S of BF33BT ceramics indicate their potential as new low-cost eco-friendly lead-free piezoceramics.