Lead-free Piezoelectric Ceramics Research Articles

Contribution of (Bi0.45Y0.05)Na0.5ZrO3 to induced multiphase coexistence and enhanced piezoelectric properties of K0.5Na0.5NbO3 lead-free ceramics

In this study, new lead-free piezoelectric ceramics (1 − x)(K0.5Na0.5)NbO3 (KNN)–x(Bi0.45Y0.05)Na0.5ZrO3 (BYNZ) were prepared using the conventional solid-state method, and the relation between the doping amount of (Bi0.45Y0.05)Na0.5ZrO3 and its structural and electrical properties was investigated. Material characterization and structural analyses conducted using X-ray diffraction, scanning electron microscopy, and energy-dispersive spectroscopy revealed that KNN–BYNZ ceramics formed single perovskite structures at 0 ≤ x ≤ 0.05 and a polycrystalline phase boundary (PPB) for the coexisting orthorhombic and tetragonal phases at 0.03 ≤ x ≤ 0.05. The ceramics exhibited desirable electrical properties at x = 0.04 (d33 = 305 pC/N, kp = 45.8 %, εr = 1316, tanδ = 2.4 %, Tc = 332 °C, Pr = 28.2 μC/cm2, and Ec = 1.07 kV/mm). These findings reveal that the introduction of BYNZ enables the effective formation of a PPB in the KNN-based ceramics to improve their electrical properties, and they exhibit potential for replacing lead-based piezoelectric ceramics in the market.

Ultrahigh strain and superior temperature stability in lead-free ceramics via synergetic texture technique and phase structure engineering

Lead-free piezoelectric ceramics with large strain response and good temperature stability are highly required for actuator applications. However, the search for lead-free ceramics with both enhanced strain and reduced thermal-dependent behavior is a great challenge. In this work, by employing templated grain growth technique and elaborately modulate the phase structure, large unipolar strain of 0.30%, low strain hysteresis Hs~12%, along with small strain variation 11.8% between 20-100oC are achieved in (001)C-oriented (Ba0.95Ca0.05)(Sn0.04Ti0.96)O3 ceramics, being the optimal level of BaTiO3 family. It is revealed the ceramics exhibit a coexistence of orthorhombic and tetragonal phases. The inherent piezoelectric anisotropy of orthorhombic phase, the reversible a→c domain switch, along with the refined non-180o domain structures contribute to the remarkable electrostrain characteristic. This study proposed a promising strategy to develop high performance piezoelectric materials for actuator applications.

Tuning phase structure for enhanced electrostrain in Nb5+-doped Bi0.5(Na0.81K0.19)0.5TiO3 lead-free piezoelectric ceramics

Tuning phase structure for enhanced electrostrain in Nb5+-doped Bi0.5(Na0.81K0.19)0.5TiO3 lead-free piezoelectric ceramics

Enhanced electric field-induced strain performance in 0–3 composite ceramics by strain and polarization coupling

Inferior electric field-induced strain and large hysteresis in the high-temperature (1-x)BiFeO3-xBaTiO3-based piezoceramics under low driving electric field, which restricts their practical applications, are dramatically technical bottlenecks. Herein, we successfully prepare the 0–3 type composite piezoceramics with super strain properties under a small electric field. Electric field-induced strain and normalized strain coefficient in the 0–3 composite piezoceramics have been severally increased by 161% and 215% than those of non-composite piezoceramics, and the hysteresis and remnant strain in the 0–3 composite piezoceramics have been decreased by 230% and 165% compared with non-composite piezoceramics. Superior electric field-induced strain properties originate from strain and polarization couple, promoting domain switching at low driving electric field, and the novel strategy will accelerate the development and practical applications of lead-free piezoelectric ceramics.

Temperature-dependent synchrotron XRD study and electrical properties of the (1-x)BZT-(x)BCT lead-free piezoceramics

In recent years, researchers have shown the feasibility of the BZT-xBCT lead-free piezoelectric ceramics for using in various applications such as actuator, energy harvester, high-frequency ultrasonic transducer, etc. However, little evidence of temperature-dependent electrical properties of the BZT-xBCT ceramic was found. Moreover, some researchers have utilized Raman spectroscopy to observe the phase transition of the BZT-xBCT ceramic, but the Raman spectra of ferroelectric polymorphic phases are almost identical and hard to distinguish. In contrast, synchrotron radiation exhibits a high degree of monochromatization and collimation with smaller wavelength than x-ray tubes, resulting in the improvement of resolution for identifying the overlapping peaks. Therefore, this work aims to determine phase coexistence of the BZT-xBCT ceramic near phase boundary region by using high-resolution synchrotron x-ray powder diffraction in comparison with the temperature-dependent electrical properties. This work found that the occurrence of thermally-induced polymorphic phase transformations for the BZT-xBCT ceramics plays a significant role in the observed temperature-dependent electrical properties. Moreover, this work observed a trace of surface damaged layer (the presence of low-angle shoulder in the synchrotron XRD profiles) from mechanical grinding during sample preparation for XRD measurement, which has not previously been found in the BZT-xBCT ceramics. These finding will help to better understand the temperature-dependent functional properties of the BZT-xBCT ceramic for transferring into practical applications.

Achieving large strain and low hysteresis in BiFeO3-BaTiO3-based piezoelectric ceramics

The high strain hysteresis has impeded lead-free piezoelectric ceramics to replace lead zirconate titanate ceramics applied in actuators. In this study, we report a significant advancement with the synthesis of a novel BiFeO3-BaTiO3-(Ba0.6Sr0.4)TiO3 (BF-BT-BST) system. The optimal composition has demonstrated a remarkable strain of 0.42 % coupled with a notably low hysteresis of 21 %. It is found that the incorporation of BST into BF-BT facilitates the transition from the rhombohedral phase to the pseudo-cubic phase, which in turn significantly enhances the relaxor ferroelectric characteristics of the ceramic. Through adjusting the composition proportion of BST, a unique ferroelectric domain structure is established for the BF-BT-0.04BST ceramic, where polar nanoregions (PNRs) are surrounded by ferroelectric macrodomains. The domain structure enables the ceramic to have the ability to respond the external electric field quickly compared to the PNRs for typical relaxor composition, thereby leading to large strain and low hysteresis simultaneously. Hence, it is inferred that the ferroelectric macrodomains simplify the response process of the PNRs under electric field. This study provides an efficient strategy to break through the bottleneck of large strain hysteresis for BF-BT ceramic, and gives a deep comprehension for the improvement of the strain characteristics.

Ultra-high strain in Bi0.5(Na0.41K0.09)TiO3 Pb-free piezoelectric ceramics modified by Sr(Hf0.5Sb0.4)O3

The lead-free piezoelectric ceramics used in piezoelectric actuators have attracted extensive attention owing to their substantial electric-field-induced strain. In this study, The (1-x)Bi0.5(Na0.41K0.09)TiO3-xSr(Hf0.5Sb0.4)O3 (BNKT-xSHS) piezoelectric ceramics were synthesized using the conventional solid-state reaction method. The impact of SHS substitution on the microstructure and electrical properties was systematically explored. Among them, the BNKT-0.015SHS sample, featuring ergodic relaxor states, demonstrates a high piezoelectric strain coefficient (d33*) of 785 p.m./V under a low electric field of 50 kV/cm(Strain = 0.392 %). It exhibits a repeatable strain value of 0.47 % under an 80 kV/cm electric field(d33* = 590 p.m./V). Moreover, the strain values remain around 0.4 % between room temperature and 100 °C, with variations within 90 %. The heightened repeatable strain response is considered to be linked to the electric field-induced reversible phase transition occurring within the ergodic relaxor state. The higher strain temperature stability is ascribed to the coexistence of quadrilateral polar nanoregions and rhombic polydomain nanoregions. This study provides an effective example for achieving significant strain responses, presenting a feasible candidate material for applications in piezoelectric actuators.

The Effect of Bi0.5Li0.5ZrO3-SrSnO3 Composite Doping on the Construction of Polymorphic Phase Boundaries and Enhanced Electrical Properties of K0.45Na0.55Nb0.965Sb0.035O3 Piezoelectric Ceramics

In this experiment, a new lead-free piezoelectric ceramics (1−x)K0.45Na0.55Nb0.965Sb0.035O3−x(0.9Bi0.5Li0.5ZrO3−0.1SrSnO3) were prepared by the conventional solid-phase method, and the effects of the doping amount of 0.9Bi0.5Li0.5ZrO3−0.1SrSnO3 on the K0.45Na0.55Nb0.965Sb0.035O3 ceramics on the crystal structure, microstructure, microscopic structure and electrical properties. All the doping ions entered the KNN lattice and formed a dense solid solution with a single-phase structure, and the phase structure of the ceramics coexisted from orthorhombic (O) to orthorhombic-tetragonal (O-T) phases in the range of 0 ≤ x ≤ 0.03, and transitioned to rhombohedral-tetragonal (R-T) phase coexistence when 0.035 ≤ x ≤ 0.05. The electrical properties of the ceramics were analyzed and the polymorphic phase boundary (PPB) region was obtained at x = 0.035 and had the best overall properties: d 33 = 324pC/N, k p = 49%, ε r = 1479, tanδ = 3.21%, P r = 31.98 μC/cm2, E c = 16.83 kV cm−1 and T C = 293°C. By The microstructural analysis of the ceramics showed that the appropriate amount of compound doping of the second element enhances the denseness of the ceramics as well as makes the grains uniformly distributed. These results indicate that the ceramics of this system have great prospects for future applications in the field of lead-free piezoelectric ceramics.

Contribution of irreversible non-180° domain to performance for multiphase coexisted potassium sodium niobate ceramics

Despite the dominance of lead-based piezoelectric materials with ultrahigh electric-field-induced strain in actuating applications, seeking eco-friendly substitutes with an equivalent performance remains an urgent demand. Here, a strategy of regulating the irreversible non-180° domain via phase engineering is introduced to optimize the available strain (the difference between the maximum strain and the remnant strain in a unipolar strain curve) in the lead-free potassium–sodium niobate-based piezoelectric ceramics. In situ synchrotron X-ray diffraction and Rayleigh analysis reveal the contribution of the non-180° domain to available strain in the tetragonal–orthorhombic–rhombohedral phase boundary. The reducing orthorhombic phase and increasing rhombohedral/tetragonal phase accompanied by the reduced irreversible non-180° domain are obtained with increasing doping of Sb5+, resulting in an enlarged available strain due to the significantly lowered remnant strain. This optimization is mainly attributed to the reduced irreversible non-180° domain wall motion and the increased lattice distortion, which are beneficial to decrease extrinsic contribution and enhance intrinsic contribution. The mesoscopic structure of miniaturized nanosized domain with facilitated domain switching also contributes to the enhancement of available strain due to the improved random field and decreased energy barrier. The study will shed light on the design of lead-free high-performance piezoelectric ceramics for actuator applications.

Young’s modulus and damping of partially sintered potassium sodium niobate (KNN) ceramics and its temperature dependence determined via the impulse excitation technique (IET)

Potassium sodium niobate (KNN) is suitable for the preparation of lead-free piezoelectric ceramics, and thus the elastic properties and damping behavior should be reliably known for practical applications. In this work we compare partially sintered KNN ceramics prepared by uniaxial and conventional sintering from three different KNN powders and show that the impulse excitation technique (IET) is perfectly suited to determine Young’s modulus at room temperature as well as the temperature dependence of Young’s modulus and damping (heating-cooling cycles with maximum temperature 800 °C). Room temperature values of the effective Young’s modulus of partially sintered KNN ceramics are below the predictions for convex pores and above a recently published numerical benchmark relation for concave pores. The phase transition temperatures determined by the IET are 160–190 °C for the low-temperature orthorhombic-tetragonal / tetragonal-orthorhombic transition and 388–412 °C for the high-temperature tetragonal-cubic / cubic-tetragonal transition, with hysteresis 12–25 K.

Advancing energy storage capabilities in 0.7BNST(1-x)-0.3BLMNx lead-free dielectric ceramic materials

Lead-free ferroelectric ceramics with a composition of 0.7(Bi0.5Na0.5)0.7Sr0.3Ti(1-x)O3-0.3Ba0.94La0.04(Mg1/3Nb2/3)xO3 (abbreviated as 0.7BNST(1-x)-0.3BL(MN)x, 0 ≤ x ≤ 0.12) were prepared using solid-phase sintering method, involving co-substituting at A and B sites. High recoverable energy density (Wrec) of 3.54 J/cm3 and energy efficiency (η) 85.49% are achieved at an electric field of 270 kV/cm. Furthermore, these ceramics exhibited excellent temperature and cycle stability at 120 kV/cm (within 25 °C–150 °C, Wrec fluctuation range <14 %; under 1∼106 cycles, the Wrec fluctuation range <5 %). In terms of dielectric performance, they exhibited a high dielectric constant (εr∼4540), an extremely low dielectric loss tanδ of <0.04 (30 °C–300 °C), and good temperature stability with Δε/ε150 °C ≤ ±15 % (−19.5 °C–233.4 °C). During the charging and discharging process, these ceramics demonstrated a high energy density (Wd) of 1.2 J/cm3, a power density (PD) of 61.7 MW/cm3, and an extremely short discharge time (t0.9) of approximately ∼0.11 μs＀ This study has improved the dielectric energy storage performance of BNT-based lead-free piezoelectric ceramics, making them suitable for use in pulse power devices.

Enhancement of Density and Piezoelectric Properties of 0.96(K0.456Na0.536)Nb0.95Sb0.05-0.04Bi0.5(Na0.82K0.18)0.5ZrO3 Lead-Free Piezoelectric Ceramics through Two-Step Sintering Method

Enhancement of Density and Piezoelectric Properties of 0.96(K0.456Na0.536)Nb0.95Sb0.05-0.04Bi0.5(Na0.82K0.18)0.5ZrO3 Lead-Free Piezoelectric Ceramics through Two-Step Sintering Method

Bismuth Ferrite-Based Lead-Free High-Entropy Piezoelectric Ceramics.

Piezoelectric ceramics, as essential components of actuators and transducers, have captured significant attention in both industrial and scientific research. The "entropy engineering" approach has been demonstrated to achieve excellent performance in lead-based materials. In this study, the "entropy engineering" approach was employed to introduce the morphotropic phase boundary (MPB) into the bismuth ferrite (BF)-based lead-free system. By employing this strategy, a serial of novel "medium to high entropy" lead-free piezoelectric ceramics were successfully synthesized, namely (1-x)BiFeO3-x(Ba0.2Sr0.2Ca0.2Bi0.2Na0.2)TiO3 (BF-xBSCBNT, x = 0.15-0.5). Our investigation systematically examined the phase structure, domain configuration, and ferroelectric/piezoelectric properties as a function of conformational entropy. Remarkable performances with a largest strain of 0.50% at 100 kV/cm, remanent polarization ∼40.07 μC/cm2, coercive field ∼74.72 kV/cm, piezoelectric coefficient ∼80 pC/N, and ∼500 pm/V were achieved in BF-0.4BSCBNT ceramics. This exceptional performance can be attributed to the presence of MPB, coexisting rhombohedral and cubic phases, along with localized nanodomains. The concept of high-entropy lead-free piezoelectric ceramics in this study provides a promising strategy for the exploration and development of the next generation of lead-free piezoelectric materials.

Giant piezoelectric response and structure evolution of Bi0.5(Na0.3K0.3Li(0.4-x)Bax)0.5ZrO3 modified (K0.48Na0.52)(Nb0.95Sb0.05)O3 lead-free piezoelectric ceramics

The composition of materials can significantly affect the structure and properties of KNN based piezoelectric ceramics. Here, 0.965(K0.48Na0.52)(Nb0.95Sb0.05)O3-0.035Bi0.5(Na0.3K0.3Li(0.4-x)Bax)0.5ZrO3 ceramics were designed and synthesized using CuO as a sintering aid to promote densification of ceramics. The results show that these ceramics had orthorhombic-tetragonal phase transition structure, and the ratio of the two phases becomes an important factor affecting the electrical properties. When the ratio of the two is close, the piezoelectric performance is optimized. Under specific composition, the sample exhibits a large piezoelectric effect, with the piezoelectric constant and inverse piezoelectric constant reaching 347 pC/N and 1052 p.m./V, respectively. These results prove that rational composition and structure modulation can effectively improve the performance of KNN-based lead-free piezoelectric ceramics, making it a promising alternative for lead-based piezoelectric ceramic materials.

Low-frequency directional wideband transducer based on lead-free piezoelectric ceramics

In recent years, lead-free piezoelectric ceramic devices have been extensively researched and applied in the high-frequency range, specifically above 20 kHz, for airborne acoustics applications. However, few applications have been reported on low-frequency underwater acoustic transducers, which are crucial in the fields of underwater acoustic communication, ocean resource development, etc., because this imposes more stringent requirements for lead-free piezoelectric ceramics in terms of size, mechanical coupling coefficient, piezoelectric coefficients, and temperature stability. This paper explores the application of high-performance potassium sodium niobate based lead-free piezoelectric ceramics in a low-frequency directional wideband transducer. It covers design, fabrication, and performance testing of the transducer. The transducer measures Φ236 × 83 mm2 and weighs 4.45 kg, which achieves wideband emission (3500–8200 Hz) and directional sound emission with a front-to-back sound pressure ratio exceeding 6 dB across a significant frequency range. Both the theoretical analysis and the experimental results confirm the competitiveness application of the lead-free piezoelectric ceramics in the field of low-frequency underwater acoustic transducers applications.

Enhanced insulation and ferro/piezo-electric properties of BiFeO3–BaTiO3via synchronous B-site co-doping and quenching treatment

Lead-free piezoelectric ceramics 0.7BiFe1-x(Zn0.5Sn0.5)xO3-0.3BaTiO3 [BF(ZS)x-BT] were successfully prepared using the solid-state reaction method. The dual effects of B-site Zn/Sn co-doping and quenching on the structure and piezoelectricity of BF(ZS)x-BT were investigated. All samples showed a distinct perovskite structure, characterized by the simultaneous presence of rhombohedral (R) and pseudo-cubic (pC) phases. The insulation and electrical properties were significantly increased by appropriate Zn/Sn co-doping and quenching treatment. The long parallel strip domains and enhanced lattice distortion synergistically contribute to the outstanding piezoelectricity (d33 = 203 pC/N) and a high Curie temperature (Tc = 493 °C) in quenched BF(ZS)0.003-BT. Furthermore, the quenching treatment was found to further improve the piezoelectric property and enhance its high-temperature stability, as demonstrated by the in-situ electromechanical coupling coefficient (kp) and thermal depolarization test. The d33 of the quenched BF(ZS)0.003-BT was maintained at 186 pC/N around 400 °C, highlighting its promising applications in medium-high temperature conditions.

BNH doping enhances the piezoelectric properties and temperature stability of KNN-based lead-free piezoelectric ceramics

BNH doping enhances the piezoelectric properties and temperature stability of KNN-based lead-free piezoelectric ceramics

Deciphering the structural heterogeneity behaviors of (K, Na)NbO[formula omitted]-based piezoelectric ceramics with multi-scale analyses

Inducing local structural heterogeneity is one of the most attractive strategies to enhance the piezoelectricity in lead-free piezoceramics, while the underlying mechanisms have not been well clarified, such as phase coexistence and domain boundary. Here, we mainly focus on analyzing the structure evolution mechanism of 0.96(K0.48Na0.52)(Nb1−xSbx)O3-0.04(Bi0.5Ag0.5)ZrO3 (0≤x≤0.1) (KNN) lead-free piezoelectric ceramics to study the intrinsic structural contributions from chemical modifying and/or alloy replacement. We explore the relation between structural characteristics and physical functionality by combining macro-spectral and micro-heterogeneity characterizations. It was found that Raman- and infrared-active phonon evolutions with respect to the motion of oxygen octahedron reveal the enhanced lattice symmetry when x increases to 0.06, along with the upswing optical electronic transitions. Moreover, we clarify the local heterogeneous structure of ceramics in terms of the spatial distribution of phonon traits on the micron scale accompanied with the atom-resolution polar vector state. The detected nanoscale atomic displacement clusters are directly related to the excellent polarization properties. Additionally, the phonon thermodynamics evolution was investigated in a wide temperature range of 80-720 K with unpolarized and polarized geometries. The detailed phase transition evolution and rhombohedral–orthorhombic–tetragonal multi-phase coexistence have been confirmed with Sb incorporation. The present work boosts the understanding of the compound-structure-functionality relation of KNN-based heterophase coexistent system, which could promote the development of the promising high-performance piezoelectric materials.

An interpretable machine learning strategy for pursuing high piezoelectric coefficients in (K0.5Na0.5)NbO3-based ceramics

Perovskite-type lead-free piezoelectric ceramics allow access to illustrious piezoelectric coefficients (d33) through intricate composition design and experimental modulation. Developing a swift and accurate technology for identifying (K, Na)NbO3 (KNN)-based ceramic compositions with high d33 in exceedingly large “compositional” space will establish an innovative research paradigm surpassing the traditional empirical trial-and-error method. Herein, we demonstrate an interpretable machine learning (ML) framework for quick evaluation of KNN-based ceramics with high d33 based on data from published literature. Specifically, a thorough feature construction was carried out from the global and local dimensions to establish tree regression models with d33 as the target property. Subsequently, the feature-property mapping rules of KNN-based piezoelectric ceramics are further optimized through feature screening. To intuitively understand the correlation mechanisms between ML regression targets and features, the sure independence screening and sparsifying operator (SISSO) method was employed to extract the essential descriptors to explain d33. A straightforward descriptor, e(NMB−MVB)⋅ST/(IDA)2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\ ext{e}}^{({{NM}}_{\ ext{B}}-{{MV}}_{\ ext{B}})}\\cdot {ST}/{(I{D}_{\ ext{A}})}^{2}$$\\end{document}, consisting of only four easily accessible parameters, can accelerate the evaluation of a series of novel KNN-based ceramics with high d33 while exhibiting strong theoretical interpretability. This work not only provides a tool for the rapid discovery of high piezoelectric performance in KNN-based ceramics but also offers a data-driven route for the design of property descriptors in perovskites.

Simultaneously realizing high piezoelectricity and thermal stability in BNT-based ceramics via integrating layered diffusion and thermal treatment

An inherent conflict of (Bi0.5Na0.5)TiO3-based (BNT) lead-free piezoelectric ceramics is the optimizing piezoelectric response (d33) with deteriorating depolarization temperature (Td), which severely restricts the further achievements of BNT-based ceramics. A new strategy is proposed in this work to simultaneously realize high piezoelectric property (d33 = 140 pC/N) and thermal stability (Td = 232 °C) in BNT-based ceramics by integrating layered composite structure of 0.89(Bi0.5Na0.5)TiO3-0.11BaTiO3 with high Td and 0.87(Bi0.5Na0.5)TiO3-0.11BaTiO3-0.02(Sm0.5K0.5)TiO3 with large d33 (BNT1/BNT2) and thermal treatment processes. In the layered composite ceramics, the composition difference induces a built-in field (Eb) that promotes the diffusion of ferroelectric-relaxor (FE-RE) phase transition in the ceramics, delaying the Td to 185 °C. In addition, the thermal treatment processes facilitate both the Eb expansion, stabilize the d33 over a wide temperature range, as well as enlarge the grain size to elevate the d33 from 133 pC/N to 145 pC/N. Hence, the strategy we proposed is promising to offer a new paradigm for designing piezoelectric materials with high piezoelectric response over a wide temperature range.