Lead-free Piezoceramics Research Articles

Additive manufacturing of lead-free KNN by binder jetting

Additive manufacturing of lead-free piezoceramics is of great interest, given the large request of application-oriented designs with optimal performances and reduced material consumption. Binder Jetting (BJ) is an additive manufacturing technique potentially suited to the production of ceramic components, however the number of feasibility studies on BJ of piezoceramics is extremely limited and totally lacking in the case of sodium-potassium niobate (KNN). In this work, as-synthesised powders are employed in the BJ 3D printing process. Microstructural properties, such as porosity, grain size distributions, and phase composition are studied by SEM, XRD and MIP (Mercury Intrusion Porosimetry) and compared to die-pressed pellets. Analyses reveal considerable residual porosity (~40%) regardless of the printing parameters, with a weak preferential orientation parallel to the printing plane. The piezoelectric characterization demonstrates an outstanding d33 value of 80–90 pC N−1. Finally, Figures of Merits for the employment as porous piezoceramics in the direct mode are presented.

(K, Na)NbO3-based lead-free piezoceramics: one more step to boost applications.

This perspective summarizes the research status of environmentally-benign KNN-based piezoceramics, and proposes the potential strategies for further designing KNN-based materials with simultaneously enhanced comprehensive performance (d33 and Qm), which would be conducive to boost their applications.

Reduction inhibition of Fe3+ ions in Mn-doped 0.7BiFeO3-0.3BaTiO3 ceramics by direct reaction sintering

The structural, piezoelectric, ferroelectric, and dielectric properties of Mn-modified 0.7Bi1.02FeO3-0.3BaTiO3 (0.7BF-0.3BT) lead-free piezoceramics prepared by direct reaction sintering (DRS) and conventional process (CP) were investigated in present study, respectively. Experimental analysis showed that the addition of small amounts of Mn4+ ions could enhance the piezoelectric properties of the BF-BT solid solution. The XPS results indicated that the DRS samples exhibited a higher ratio of Fe3+/Fe2+, and thus fewer oxygen vacancy defects. The piezoelectric constant d33 of the 0.7BF-0.3BT-0.2mol%Mn ceramics prepared by DRS is as high as 172 pC/N, Curie temperature measured is 459 °C, and the relative dielectric constant εr and dielectric loss tanδ at room temperature are 804 and 0.058, respectively, which are superior to those of the CP ceramics under the same sintering temperature. Therefore, the present study suggests that the dielectric and piezoelectric properties of Mn-doped BF-BT ceramics could be greatly enhanced via the DRS process, which provides a promising alternative to the CP for a more cost-effective preparation for BF-BT ceramics.

High strain in Bi0.5Na0.5TiO3-based relaxors by adding two modifiers featuring with morphotropic phase boundary

The electric field-induced strain in lead-free piezoceramics is generally limited to less than 0.4%, which hinders their practical applications such as actuator. Herein we report a new composition of 0.94Bi0.5Na0.5TiO3-0.06Ba0.85Ca0.15Ti0.9Zr0.1O3-xLi0.06(K0.5Na0.5)0.94NbO3 (BNT-BCZT-xLKNN) ceramics by adding two modifiers (i.e., Li0.06(K0.5Na0.5)0.94NbO3 and Ba0.85Ca0.15Ti0.9Zr0.1O3) featuring with a morphotropic phase boundary (MPB) into the Bi0.5Na0.5TiO3 system. The BNT-BCZT-0.02LKNN shows a high strain of 0.5% as well as a strain-electric field ratio (Smax/Emax) of 625 pm/V, which is one of the best performances compared with reported lead-free piezoceramics. Rietveld refinement and microstructure analysis confirmed the existence of tetragonal (P4bm) and rhombohedral (R3c) phases, and a small part of ferroelectric domains embedded into relaxors according to the PFM, both facilitating the relaxor-to-ferroelectric transformation under an external electric field. As a result, a high strain is obtained in the BNT-BCZT-LKNN system. Our work provides an effective strategy for designing novel lead-free materials with high strain.

A correlative study between the microstructure and electrical properties of lead-free piezoceramics (1-x)BHT-xYLG driven by the synergistic action of multiple factors

Piezoceramics are important functional materials with broad applications in electronics, communication, medicine, and energy. Increasing environmental protection and human health concerns about the toxicity of lead have impelled the development of lead-free piezoceramics. At this work, in combination with phase field simulation, grain growth mechanism, ferroelectric domain wall model, and defect dipole formation mechanism, (1-x)Ba(Hf0.02Ti0.98)O3-x(Y0.5Li0.5)GeO3 [(1-x)BHT-xYLG, x = 0–0.40 mol%] lead-free piezoceramics were designed and fabricated via the two-step synthesis and solid-state reaction method, which yielded superior comprehensive electrical property. Phase field simulation respectively simulates the distribution of ferroelectric domains of O and T phase under different external electric fields (0–20 kV/mm) and the phase states under different temperatures (−100 to 150 °C). This research finds that their electrical properties are affected by the synergistic action of multiple factors, e.g., orthorhombic-tetragonal phase boundary (O-T PB), grain size (GS), domain-wall (DW), and defect dipole (DD), etc., rather than any single factor.

Lead-free, high-current output piezoelectric nanogenerators using three-dimensional interdigitated electrodes

Harvesting mechanical energy based on piezoelectricity has attracted extensive attention, but achieving lead-free piezoelectric nanogenerators (PENGs) with high output current is still a big challenge, which severely limit their wide applications. Here, to address it, flexible composites with excellent piezoelectric capability are proposed and used to fabricate lead-free, high-current output PENGs using three-dimensional (3-D) interdigitated electrodes. By forming heterojunctions of Ag/(Ba,Ca)(Zr,Ti)O3 (Ag/BCZT), polarization charges in BCZT nanowires unidirectionally transfer to Ag nanoparticles under external force, resulting in the enhanced piezoelectric outputs of Ag/BCZT nanowires embedded PVDF composites macroscopically. By creating multi-layered PENGs using 3-D interdigitated electrodes (IPNGs), the total amount of polarization charges increased, giving rise to the significantly improved output current. Optimally, the 4-unit IPNG can generate a proper voltage of 20 V and a considerable current of 15 μA (corresponding current density is 3.75 μA/cm2), which is higher than the other lead-free piezoceramics based PENGs previously. The excellent outputs can also charge a 1 μF capacitor from 0 V to 5.3 V in 30 s (equivalent charge density is 272 μC/m2). This work presents a brand-new paradigm for high-performance PENGs from the perspective of material and device design.

Band gap, complex dielectric function, and optical properties of Sb-doped lead-free KNN piezo-ceramics analyzed by VEELS-TEM

Sb-doped KNN (Na0.9K0.1Nb0.97Sb0.03O3, KNNS) is an environment-friendly lead-free ferroelectric and it has high piezoelectric response. A band gap energy Eg = 3.58 eV for KNNS was evaluated by valence electron energy loss spectroscopy (VEELS), which has not been reported in the literature. The zero loss peak (ZLP) was extracted by the reflected tail model, results were gotten by the Fourier-log method. Single scattering dispersion (SSD) was used to execute the Kramers-Krӧnig analysis, thence: complex dielectric function (ε1 and ε2) based on KNNS, and optical properties were obtained; The static refractive index n(0)(nKNNS) resulted to be 2.21, which mathematically is about a square root of dielectric constant, coinciding with that obtained experimentally. Also, a peak at n1=4.1 eV and n2=9.42 eV located in the near ultraviolet was observed. Understanding the different applications of KNNS in optoelectronic devices is vital, also it is worth mentioning that many articles overlook the relativistic effects in the band gap, dielectric function, and the optical properties measurements.

Application of [001]-textured (K, Na)(Nb, Sb)O3-CaZrO3 thick films to piezoelectric energy harvesters

A (K, Na)NbO3 (KNN)-based lead-free piezoceramic for a piezoelectric energy harvester (PEH) should exhibit a large kij, Qm, dij, and a small εT33 to generate a large power output. Texturing was used to enhance the piezoelectricity of KNN-related piezoceramics. In particular, the kij and dij values of the KNN-based piezoceramics were considerably improved after texturing along the [001] direction, with a small change in the εT33/ε0 value, indicating that the [001]-textured KNN-based thick films are good candidates for use in PEHs. The 0.97(K0.5Na0.5)(Nb0.93Sb0.07)O3-0.03CaZrO3 [KN(N0.93S0.07)-CZ] thick film was textured along the [001] direction, and this thick film exhibited a large kp (0.57) and d33 × g33 (25.7 pm2/N), which is the largest d33 × g33 of the KNN-based piezoceramics reported to date. A cantilever PEH fabricated using the textured KN(N0.93S0.07)-CZ thick film exhibited a power density of 21.4 μW/mm3 at the resonance frequency. This is the highest power density observed for PEHs fabricated using lead-free piezoceramics. The PEH also exhibited a power density of 0.023 μW/mm3 at the off-resonance frequency. Therefore, the textured KN(N0.93S0.07)–CZ thick film is a good candidate for use in PEHs.

Selectively designed Fe doping of lead-free BaTiO3 piezoceramics

Selectively designed Fe doping of lead-free BaTiO3 piezoceramics

Microscopic origin of the enhanced piezoelectric thermal stability in acceptor doped lead-free Ba(Ti0.8Zr0.2)O3-50(Ba0.7Ca0.3)TiO3 ceramic

Acceptor doping is effective in enhancing thermal stability in piezoceramics, while the reason underlying is still unclear and awaits explanation. In this work, through doping acceptor Mn in lead-free Ba(Ti 0.8 Zr 0.2 )O 3 -50(Ba 0.7 Ca 0.3 )TiO 3 ceramic, our results show that doping Mn achieves higher depolarization temperature, even higher than Curie temperature ( T C ) and simultaneously a better piezoelectric thermal stability. Through microscopic and macroscopic analysis, the enhancement can be explained by the clamping effect induced by acceptor doping, which is carefully demonstrated by symmetry-conforming short-range ordering tendency theory. Thus, this work reveals the mechanism for enhanced depolarization temperature and piezoelectric thermal stability due to acceptor doping and will help developing new thermal stable lead-free piezoceramics applicable in a wider temperature range.

Analysis of the structure and conductance of Mg2+ acceptor-doped CaBi2Nb2-xMgxO9-3x/2 piezoceramics

In this work, Mg2+-doped CaBi2Nb2O9 (CBN-xMg) lead-free piezoceramics were prepared by a common solid-state method to investigate the effects of Mg2+ doping content on crystal structure, electrical resistivity, and dielectric and ferroelectric properties. XRD and Raman spectroscopy show that the Mg atoms enter the B-site to form a solid solution of the pure CBN phase. In addition, the XRD refinement results show that Mg2+ doping increases the distortion of the NbO6 octahedron and simultaneously enhances the total contribution of the spontaneous polarization of each position along the a-axis, and that the Ps increases from -28.678 μC/cm2 for x = 0 to -31.768 μC/cm2 for x = 0.02. However, when x > 0.02, the polarization decreases due to the oxygen vacancy pinning effect. According to SEM analysis, Mg2+ doping strengthened the growth rate of CBN ceramic grains on the a-b plane, resulting in a more obvious plate-like structure. The reduced anti-site defects of the CBN ceramic samples strengthened the structure of (Bi2O2)2+ and improved the resistivity of the samples. The internal dipole moment was also strengthened, resulting in a significant increase in the dielectric constant and a decrease in the dielectric loss. In general, Mg2+ doping significantly improved the comprehensive properties of CBN ceramics, with improved values including a d33 of 11.1 pC/N, Pr of 7.22 μC/cm2, tanδ (600 °C) of 3.0%, and ρdc (600 °C) of 108 Ω•cm.

High d33 Lead-Free Piezoceramics: A Review

High d33 Lead-Free Piezoceramics: A Review

Investigation of approaches to the BaTiO-=SUB=-3-=/SUB=- piezoceramics production: the influence of the shaping method and the powder particles size

For the first time, the possibility of obtaining samples of BaTiO3 piezoceramics with d33 values between 240-270 pC/N from commercially available powder by vibrational pressing (vibropressing) and semi-dry pressing without the use of expensive methods of doping and/or alloying the initial powder and texturing piezoceramics is shown. The method of vibropressing with a pressure of 10 MPa allows to get similar structure and properties of samples, as well as the method of semi-dry pressing with a pressure of 100 MPa. Keywords: lead-free piezoceramics, barium titanate, piezoelectric properties, vibration pressing, pressing.

Determination of the polymerization depths of lead-free piezoceramic pastes for UV 3D printing

In present study, the polymerization depths for the implementation of the laser stereolithography process in the system (oligomer - piezoceramics) on the wavelengths of 445-465 nm UV range were determined in the original BTO, KNN and NBT lead-free piezoceramic pastes. It was shown that powder pastes, which provide a polymerization depth more than 150 μm, are promising for using in 3D printing. Such depth was chosen to guarantee a sufficient overlap of neighboring layers during polymerization, at the laser beam velocity speed from 1 m/s and the distance between the laser paths of 50 μm. For NBT pastes, successful photo polymerization was carried out for the first time, and for KNN paste the process performance was significantly increased. Keywords: lead-free piezoceramics, stereolitography (SLA) - based ceramics 3D printing, UV- curing and bandwidths

Phase Structure and Piezoelectric Property of (Ba0.85Ca0.15)(Ti0.9Zr0.1-xSnx)O3 Lead-free Piezoceramics

Phase Structure and Piezoelectric Property of (Ba_0.85Ca_0.15)(Ti_0.9Zr_0.1-<i>_x</i>Sn<i>_x</i>)O₃ Lead-free Piezoceramics

(K, Na)Nbo 3 Lead-Free Piezoceramics Prepared by Microwave Sintering and Solvothermal Powder Synthesis

(K, Na)Nbo 3 Lead-Free Piezoceramics Prepared by Microwave Sintering and Solvothermal Powder Synthesis

Large piezoelectricity in NaNbO3-based lead-free ceramics via tuning oxygen octahedral tilt.

The development of high-performance lead-free piezoceramics for replacing Pb-based perovskites has attracted lots of attention, and comparable room-temperature piezoresponse has been realized in (Na,K)NbO3 and BaTiO3-based ceramics with local structure heterogeneity via adjusting polymorphic phase boundary. In this work, a new method of oxygen octahedron tilt design is used in NaNbO3-based lead-free ceramics, which usually shows complex oxygen octahedron tilt information inherited from NaNbO3. The substitution of Ba(Fe0.5Nb0.5)O3 and BaTiO3 with high tolerance factor into NaNbO3 leads to a gradual elimination of anti-parallel cation displacement and anti-phase tilt along the three axes; as a result, a single tetragonal phase with P4bm space group and only in-phase tilt along c axis is achieved in 0.88NaNbO3-0.04Ba(Fe0.5Nb0.5)O3-0.08BaTiO3 ceramic. Accompanying the decreased oxygen octahedral tilt degree, a drastically improved d33 up to 367 pC N-1 (over ten times that of NaNbO3 ceramic) is obtained, reaching a record high in NaNbO3-based lead-free ceramics. Together with temperature insensitive piezoresponse originating from thermally stable oxygen octahedral tilt structure, the studied NaNbO3-based materials show large potential for replacing Pb-based ceramics in some electronic devices. The oxygen octahedron tilt engineering would be used for designing more high-performance lead-free ceramics with high piezoresponse and excellent thermal stability simultaneously.

Temperature- and Stress-Dependent Electromechanical Properties of Phase Boundary Engineered (K,Na)Nbo3-Based Lead-Free Piezoceramics

Temperature- and Stress-Dependent Electromechanical Properties of Phase Boundary Engineered (K,Na)Nbo3-Based Lead-Free Piezoceramics

Feasible Way to Achieve Multifunctional (K, Na)NbO3-Based Ceramics: Controlling Long-Range Ferroelectric Ordering.

It is challenging to achieve highly tunable multifunctional properties in one piezoelectric ceramic system through a simple method due to the complicated relationship between the microscopic structure and macroscopic property. Here, multifunctional potassium sodium niobate [(K, Na)NbO3 (KNN)]-based lead-free piezoceramics with tunable piezoelectric and electrostrictive properties are achieved by controlling the long-range ferroelectric ordering (LRFO) through antimony (Sb) doping. At a low Sb doping, the slightly distorted NbO6 octahedron and the softened B-O repulsion well maintain the LRFO and induce plenty of nanoscale domains coexisting with a few polar nanoregions (PNRs). Thereby, the diffused rhombohedral-orthorhombic-tetragonal (R-O-T) multiphase coexistence with distinct dielectric jumping is constructed near room temperature, by which the nearly 2-fold increase in the piezoelectric coefficient (d33 ∼ 539 pC/N) and the temperature-insensitive strain (the unipolar strain varies less than 8% at 27-120 °C) are obtained. At a high Sb doping, the LRFO is significantly destroyed, leading to predominant PNRs. Thus, a typical relaxor is obtained at the ferroelectric-paraelectric phase transition near room temperature, in which a large electrostrictive coefficient (Q33 = 0.035 m4/C2), independent of the electric field and temperature, is obtained and comparable to that of lead-based materials. Therefore, our results prove that controlling the LRFO is a feasible way to achieve high-performance multifunctional KNN-based ceramics and is beneficial to the future composition design for KNN-based ceramics.

Giant electric field-induced strain with low hysteresis in Bi0.5Na0.5TiO3-xSr0.7Ca0.3TiO3 lead-free piezoceramics

Giant electric field-induced strain with low hysteresis in Bi0.5Na0.5TiO3-xSr0.7Ca0.3TiO3 lead-free piezoceramics