Search Results (36)

A single (Ba_0.85Ca_0.15)(Zr_0.10Ti_0.90)O₃ phase material with a tetragonal structure is processed and synthesized with a modified Pechini method using ethylenediaminetetraacetic acid and glycerol as chelating and esterifying agents, respectively. The complete chemical transformation to the desired phase is achieved at 900 °C, which is 300 °C lower than conventional synthesis methods. Its consolidation, reaching up to 91% relative density, is carried out at 1400 °C. It is clearly demonstrated that the use of ethylenediaminetetraacetic acid and glycerol reagents is particularly beneficial for inducing a homogeneous grain size distribution (10 μm), which leads to very promising electromechanical properties (d₃₃ = 451 pC/N; d₃₁ = 160 pC/N; kp = 0.40; $\epsilon {\prime }_{33}^T$ = 4790 and Q_m = 358) of the densified system. Full article

In this study, an Integrated Electronics Piezoelectric (IEPE)-type accelerometer based on an environmentally friendly lead-free piezoceramic was fabricated, and its field applicability was verified using a cooling pump owned by the Korea Atomic Energy Research Institute (KAERI). As an environmentally friendly piezoelectric material, 0.96(K,Na)NbO₃-0.03(Bi,Na,K,Li)ZrO₃-0.01BiScO₃ (0.96KNN-0.03BNKLZ-0.01BS) piezoceramic with an optimized piezoelectric charge constant (d₃₃) was introduced. It was manufactured in a ring shape using a solid-state reaction method for application to a compression mode accelerometer. The fabricated ceramic ring has a high piezoelectric constant d₃₃ of ~373 pC/N and a Curie temperature T_C of ~330 °C. It was found that the electrical and physical characteristics of the 0.96KNN-0.03BNKLZ-0.01BS piezoceramic were comparable to those of a Pb(Zr,Ti)O₃ (PZT) ring ceramic. As a result of a vibration test of the IEPE accelerometer fabricated using the lead-free piezoelectric ceramic, the resonant frequency f_r = 20.0 kHz and voltage sensitivity S_v = 101.1 mV/g were confirmed. The fabricated IEPE accelerometer sensor showed an excellent performance equivalent to or superior to that of a commercial IEPE accelerometer sensor based on PZT for general industrial use. A field test was carried out to verify the applicability of the fabricated sensor in an actual industrial environment. The test was conducted by simultaneously installing the developed sensor and a commercial PZT-based sensor in the ball bearing housing location of a centrifugal pump. The centrifugal pump was operated at 1180 RPM, and the generated vibration signals were collected and analyzed. The test results confirmed that the developed eco-friendly lead-free sensor has comparable vibration measurement capability to that of commercial PZT-based sensors. Full article

Uninterrupted breakthroughs in the room temperature piezoelectric properties of KNN-based piezoceramics have been witnessed over the past two decades; however, poor temperature stability presents a major challenge for KNN-based piezoelectric ceramics in their effort to replace their lead-based counterparts. Herein, to enhance temperature stability in KNN-based ceramics while preserving the high piezoelectric response, multilayer composite ceramics were fabricated using textured thick films with distinct polymorphic phase transition temperatures. The results demonstrated that the composite ceramics exhibited both outstanding piezoelectric performance (d₃₃~467 ± 16 pC/N; S~0.17% at 40 kV/cm) and excellent temperature stability with d₃₃ and strain variations of 9.1% and 2.9%, respectively, over a broad temperature range of 25–180 °C. This superior piezoelectric temperature stability is attributed to the inter-inhibitive piezoelectric fluctuations between the component layers, the diffused phase transition, and the stable phase structure with a rising temperature, as well as the permanent contribution of crystal orientation to piezoelectric performance over the studied temperature range. This novel strategy, which addresses the piezoelectric and strain temperature sensitivity while maintaining high performance, is well-positioned to advance the commercial application of KNN-based lead-free piezoelectric ceramics. Full article

The increasing need for wearable and portable electronics and the necessity to provide a continuous power supply to these electronics have shifted the focus of scientists toward harvesting energy from ambient sources. Harvesting energy from ambient sources, including solar, wind, and mechanical energies, is a solution to meet rising energy demands. Furthermore, adopting lightweight power source technologies is becoming more decisive in choosing renewable energy technologies to power novel electronic devices. In this regard, piezoelectric nanogenerators (PENGs) based on polymer composites that can convert discrete and low-frequency irregular mechanical energy from their surrounding environment into electricity have attracted keen attention and made considerable progress. This review highlights the latest advancements in this technology. First, the working mechanism of piezoelectricity and the different piezoelectric materials will be detailed. In particular, the focus will be on polymer composites filled with lead-free BaTiO₃ piezoceramics to provide environmentally friendly technology. The next section will discuss the strategies adopted to enhance the performance of BaTiO₃-based polymer composites. Finally, the potential applications of the developed PENGs will be presented, and the novel trends in the direction of the improvement of PENGs will be detailed. Full article

To meet the current demand for lead-free piezoelectric ceramics, a novel sol-gel synthesis route is presented for the preparation of Ba_0.85Ca_0.15Ti_0.9Zr_0.1O₃ doped with cerium (Ce = 0, 0.01, and 0.02 mol%) and vanadium (V = 0, 0.3, and 0.4 mol%). X-ray diffraction patterns reveal the formation of a perovskite phase (space group P4mm) for all samples after calcination at 800 °C and sintering at 1250, 1350, and 1450 °C, where it is proposed that both dopants occupy the B site. Sintering studies show that V doping allows the sintering temperature to be reduced to at least 1250 °C. Undoped BCZT samples sintered at the same temperature show reduced functional properties compared to V-doped samples, i.e., d₃₃ values increase by an order of magnitude with doping. The dissipation factor tan δ decreases with increasing sintering temperature for all doping concentrations, while the Curie temperature T_C increases for all V-doped samples, reaching 120 °C for high-concentration co-doped samples. All results indicate that vanadium doping can facilitate the processing of BCZT at lower sintering temperatures without compromising performance while promoting thermal property stability. Full article

(K_0.5Na_0.5)NbO₃ (KNN)-based ceramics have been extensively investigated as replacements for Pb(Zr, Ti)O₃-based ceramics. KNN-based ceramics exhibit an orthorhombic structure at room temperature and a rhombohedral–orthorhombic (R–O) phase transition temperature (T_R–O), orthorhombic–tetragonal (O–T) phase transition temperature (T_O–T), and Curie temperature of −110, 190, and 420 °C, respectively. Forming KNN-based ceramics with a multistructure that can assist in domain rotation is one technique for enhancing their piezoelectric properties. This review investigates and introduces KNN-based ceramics with various multistructures. A reactive-templated grain growth method that aligns the grains of piezoceramics in a specific orientation is another approach for improving the piezoelectric properties of KNN-modified ceramics. The piezoelectric properties of the [001]-textured KNN-based ceramics are improved because their microstructures are similar to those of the [001]-oriented single crystals. The improvement in the piezoelectric properties after [001] texturing is largely influenced by the crystal structure of the textured ceramics. In this review, [001]-textured KNN-based ceramics with different crystal structures are investigated and systematically summarized. Full article

Thin film technology shows great promise in fabricating electronic devices such as gas sensors. Here, we report the fabrication of surface acoustic wave (SAW) sensors based on thin films of (1 − x) Ba(Ti_0.8Zr_0.2)O_3−x(Ba_0.7Ca_0.3)TiO₃ (BCTZ50, x = 50) and Polyethylenimine (PEI). The layers were deposited by two laser-based techniques, namely pulsed laser deposition (PLD) for the lead-free material and matrix assisted pulsed laser evaporation (MAPLE) for the sensitive polymer. In order to assay the impact of the thickness, the number of laser pulses was varied, leading to thicknesses between 50 and 350 nm. The influence of BCTZ film’s crystallographic features on the characteristics and performance of the SAW device was studied by employing substrates with different crystal structures, more precisely cubic Strontium Titanate (SrTiO₃) and orthorhombic Gadolinium Scandium Oxide (GdScO₃). The SAW sensors were further integrated into a testing system to evaluate the response of the BCTZ thin films with PEI, and then subjected to tests for N₂, CO₂ and O₂ gases. The influence of the MAPLE’s deposited PEI layer on the overall performance was demonstrated. For the SAW sensors based on BCTZ/GdScO₃ thin films with a PEI polymer, a maximum frequency shift of 39.5 kHz has been obtained for CO₂; eight times higher compared to the sensor without the polymeric layer. Full article

Lead-based materials are widely used in piezoceramics due to their high electromechanical properties. However, due to environmental protection and sustainable development, the use of the toxic element lead (Pb) in electronic devices is strictly restricted, therefore requiring the rapid development of piezoelectric-based devices with lead-free ceramics. In this context, a lead-free doped barium titanate was studied with a dual objective. First, a new sol–gel method to synthesize Hf⁴⁺-doped BaHf_xTi_1−xO (BHT) with x = 0.05, 0.075, and 0.10 is presented. Such BHT sols were prepared at high concentrations of up to 1 M. Dilution in ethylene glycol allowed parameters (viscosity, colloid sizes, etc.) to be controlled, which ensured a time-stable sol for several months at room temperature. Second, densified bulk ceramics with attrited powders were obtained from these sols and showed very good electromechanical properties, with a thickness coupling factor of k_t = 47% (BaHf_0.05Ti_0.95O₃ sintered at 1500 °C/6 h). These results are a first step that will allow the processing of lead-free piezoelectric thick films using a sol–gel composite method for vibrational energy harvesting applications. Full article

Lead-free piezoceramics of Bi_0.5(Na_0.825K_0.175)_0.5TiO₃ with varying concentrations of x mol% Ag₂O (x = 0, 0.1, 0.3, 0.5, 0.7, 0.9, denoted as BNKT-xA) were fabricated using the solid-state technique. An extensive investigation was undertaken to analyze the structural, piezoelectric, and dielectric properties of these piezoceramics in the presence of Ag ions. There is no evidence of any secondary solid solution in the BNKT-xA piezoceramics. The ceramics with x mol% Ag₂O in BNKT still demonstrate the presence of both rhombohedral (R) and tetragonal (T) phases. The addition of Ag⁺ is helpful to increase the relative density of the BNKT-xA piezoceramics. It is noteworthy that the BNKT-0.3 mol% A piezoceramics show remarkable improvements in their properties (d₃₃ = 147 pC/N, k_p = 29.6%, ε = 1199, tanδ = 0.063). These improvements may be ascribed to the denser microstructure and the preservation of morphotropic phase boundaries between R and T phases caused by the appropriate addition of Ag cations. The addition of Ag⁺ results in the relaxor behavior of the BNKT-xA ceramics, characterized by disorder among A-site cations. With the increase in temperature, the d₃₃ value of BNKT-xA ceramics does not vary significantly in the range of 25 to 125 °C, ranging from 127 to 147 pC/N (with a change of d₃₃ ≤ 13.6%). This finding shows that piezoelectric ceramics have a reliable performance over a certain operating temperature range. Full article

The (Ba_0.85Ca_0.15) (Ti_0.90Zr_0.10)O₃ + x Y³⁺ + x Nb⁵⁺ (abbreviated as BCZT-x(Nb + Y), x = 0 mol%, 0.05 mol%, 0.1 mol%, 0.2 mol%, 0.3 mol%) lead-free piezoceramics samples were prepared by a traditional solid-state sintering method. And the effects of Yttrium and Niobium elements (Y³⁺ and Nb⁵⁺) co-doping on the defect, phase and structure, microstructure, and comprehensive electrical properties have been investigated. Research results show that the Y and Nb elements co-doping can dramatically enhance piezoelectric properties. It is worth noting that XPS defect chemistry analysis, XRD phase analysis and TEM results together show that a new phase of double perovskite structure Barium Yttrium Niobium Oxide (Ba₂YNbO₆) is formed in the ceramic, and the XRD Rietveld refinement and TEM results show the coexistence of the R-O-T phase. Both these two reasons together lead to significant performance improvements of piezoelectric constant (d₃₃) and planar electro-mechanical coupling coefficient (k_p). The functional relation between temperature and dielectric constant testing results present that the Curie temperature increases slightly, which shows the same law as the change of piezoelectric properties. The ceramic sample reaches an optimal performance at x = 0.1% of BCZT-x(Nb + Y), where d₃₃ = 667 pC/N, k_p = 0.58, ε_r = 5656, tanδ = 0.022, P_r = 12.8 μC/cm², E_C = 2.17 kV/cm, T_C =92 °C, respectively. Therefore, they can be used as potential alternative materials to lead based piezoelectric ceramics. Full article

Bismuth sodium titanate (BNT)-based, lead-free piezoelectric materials have been extensively studied due to their excellent strain characteristics and environmental friendliness. In BNTs, the large strain (S) usually requires a relatively large electric field (E) excitation, resulting in a low inverse piezoelectric coefficient d₃₃* (S/E). Moreover, the hysteresis and fatigue of strain in these materials have also been bottlenecks impeding the applications. The current common regulation method is chemical modification, which mainly focuses on forming a solid solution near the morphotropic phase boundary (MPB) by adjusting the phase transition temperature of the materials, such as BNT-BaTiO₃, BNT-Bi_0.5K_0.5TiO₃, etc., to obtain a large strain. Additionally, the strain regulation based on the defects introduced by the acceptor, donor, or equivalent dopant or the nonstoichiometry has proven effective, but its underlying mechanism is still ambiguous. In this paper, we review the generation of strain and then discuss it from the domain, volume, and boundary effect perspectives to understand the defect dipole behavior. The asymmetric effect caused by the coupling between defect dipole polarization and ferroelectric spontaneous polarization is expounded. Moreover, the defect effect on the conductive and fatigue properties of BNT-based solid solutions is described, which will affect the strain characteristics. The optimization approach is appropriately evaluated while there are still challenges in the full understanding of the defect dipoles and their strain output, in which further efforts are needed to achieve new breakthroughs in atomic-level insight. Full article

The results of the comprehensive magnetoelectric interaction research in three-layer structure Ni–piezoceramic BaTiO₃–Ni are presented. It has been theoretically shown and experimentally confirmed that, in the general case, the dependence of the magnetoelectric response has non-linear character. At low bias magnetic field, a quadratic dependence magnetoelectric response from an AC magnetic field is observed then there is a linear section, as well as at high values of the field magnetoelectric response has saturation. The obtained values of the magnetoelectric characteristics (α_Emax = 32 V(cmOe) for resonance and 437 mV/(cmOe) for field dependence) for lead-free three-layer structure barium–titanate–piezoceramic nickel are comparable with the magnetoelectric characteristics for similar structures, based on lead-containing ceramics. Full article

Lead-free ceramics 0.96(Na_0.52K_0.48)_0.95Li_0.05NbO₃-0.04CaZrO₃ (NKLN-CZ) are prepared by using the solid-state procedure and two-step synthesis technique. The crystal structure and thermal stability of NKLN-CZ ceramics sintered at 1140–1180 °C are investigated. All the NKLN-CZ ceramics are ABO₃-type perovskite phases without impure phases. With the increase in sintering temperature, a phase transition occurs in NKLN-CZ ceramics from the orthorhombic (O) phase to the concomitance of O-tetragonal (T) phases. Meanwhile, ceramics become dense because of the presence of liquid phases. In the vicinity of ambient temperature, an O-T phase boundary is obtained above 1160 °C, which triggers the improvement of electrical properties for the samples. The NKLN-CZ ceramics sintered at 1180 °C exhibit optimum electrical performances (d₃₃ = 180 pC/N, k_p = 0.31, dS/dE = 299 pm/V, ε_r = 920.03, tanδ = 0.0452, P_r = 18 μC/cm², T_c = 384 °C, E_c = 14 kV/cm). The relaxor behavior of NKLN-CZ ceramics was induced by the introduction of CaZrO3, which may lead to A-site cation disorder and show diffuse phase transition characteristics. Hence, it broadens the temperature range of phase transformation and mitigates thermal instability for piezoelectric properties in NKLN-CZ ceramics. The value of kp for NKLN-CZ ceramics is held at 27.7–31% (variance of k_p < 9%) in the range from −25 to 125 °C. The results indicate that lead-free ceramics NKLN-CZ is one of the hopeful temperature-stable piezoceramics for practical application in electronic devices. Full article

In recent decades, many studies have been conducted on the use of smart materials in order to dampen and control vibrations. Lead zirconate titanate piezoceramics (PZT) are very attractive for such applications due to their ability of delivering high energy strain in the structure. A pair of piezoelectric actuators can actively dampen the resonances of the structure, but the damping effectiveness strongly relies on its location. Damping effectiveness can be substantially increased if the structure is fully covered with PZT actuator pairs and the voltage distribution on each pair is optimized. In this way, each actuator pair contributes to the vibration attenuation and only the driving voltage’s sign, distributed on each actuator pair, needs to be identified for each resonance. This approach is here applied to the case of Euler–Bernoulli beams with constant cross-section and the optimal voltage distribution is investigated for several boundary conditions. The theoretical model results were corroborated with finite element simulations, which were carried out considering beams covered by ten PZT actuator pairs. The numerical results agree remarkably well with the theoretical predictions for each examined case (i.e., free-free, pinned-pinned, and fixed-fixed). Full article

Piezoelectric accelerometers using a lead-free (K,Na)NbO₃ (KNN) piezoceramic modified by a mixture of two Bi-based perovskites, Bi(Na,K,Li)ZrO₃ (BNKLZ) and BiScO₃ (BS), were designed, fabricated and characterized. Ring-shaped ceramics were prepared using a conventional solid-state reaction method for integration into a compression-mode accelerometer. A beneficial rhombohedral–tetragonal (R–T) phase boundary structure, especially enriched with T phase, was produced by modifying intrinsic phase transition temperatures, yielding a large piezoelectric charge coefficient d₃₃ (310 pC/N) and a high Curie temperature T_c (331 °C). Using finite element analyses with metamodeling techniques, four optimum accelerometer designs were obtained with high magnitudes of charge sensitivity S_q and resonant frequency f_r, as evidenced by two key performance indicators having a trade-off relation. Finally, accelerometer sensor prototypes based on the proposed designs were fabricated using the KNN-BNKLZ-BS ceramic rings, which exhibited high levels of S_q (55.1 to 223.8 pC/g) and mounted f_r (14.1 to 28.4 kHz). Perfect charge-to-acceleration linearity as well as broad flat frequency ranges were achieved with excellent reliability. These outstanding sensing performances confirm the potential application of the modified-KNN ceramic in piezoelectric sensors. Full article