Potassium Sodium Niobate Ceramics Research Articles

Boosting Low-E electro-strain via high-electronegativity B-site substitution in lead-free K0.5Na0.5NbO3-based ceramics

Lead-free piezoelectric actuators emerge as promising substitutes for their lead-containing counterparts to address environmental concerns. However, they often confront a trade-off between low driving electric fields and high electro-strain. Herein, a novel strategy to boost electro-strain under low electric fields is proposed by doping high-electronegativity B-site atoms into perovskite potassium sodium niobate-based ceramics. Our findings reveal that high-electronegativity B-site atoms elevate the covalency of B-O bonding, softening the short-range repulsion and introducing local multiphase coexistence. This leads to more nanoscale domain structures and lower coercive field, thereby enabling large strains to be produced at lower electric fields. Notably, a substantial 0.2 % bipolar electro-strain and 0.1 % unipolar electro-strain under 10 kV cm-1 is achieved in Sr, Sb co-doped potassium sodium niobate ceramics, with a broad working frequency and temperature range, as well as excellent fatigue resistance. This study unveils innovative insights into designing lead-free piezoelectric ceramics with remarkable electro-strain performance and low driving electric field, promising a significant advancement in lead-free piezoelectric materials science and piezoelectric actuators.

Enhancing piezoelectric coefficient and thermal stability in lead-free piezoceramics: insights at the atomic-scale

Given the highly temperature-sensitive nature of the polymorphic phase boundaries, attaining excellent piezoelectric coefficient with superior temperature stability in lead-free piezoceramics via direct compositional design remains a formidable challenge. We demonstrate the synergistic improvement of piezoelectric coefficient and thermal stability in lead-free piezoceramics via atomic-scale local ferroelectric structure design. Via modulation of the local Landau energy barrier at doping sites, we effectively mitigate fluctuations in piezoelectric d33. Our approach achieves an impressive d33 of ~430 pC/N with a minimal temperature fluctuation range (△d33 ~ 7%) across the room temperature to 100 °C in potassium sodium niobate ceramics. Further optimization through annealing extends this temperature up to 150 °C (△d33 ~ 8%) while maintaining a high d33 of ~380 pC/N, rivaling the performance of classic temperature stable lead zirconate titanate. This work establishes a framework for addressing the dilemma between high piezoelectric coefficient and inadequate temperature stability in lead-free piezoceramics.

Multi-iteration active learning for the composition design of potassium–sodium niobate ceramics with enhanced piezoelectric coefficient

The piezoelectricity of piezoceramics considerably depends on the doped compositions. However, the conventional trial-and-error approach to composition design is time-consuming and inefficient when searching for high-performance piezoceramics with various dopants. In this study, we introduce a data-driven framework to accelerate the design and discovery of lead-free (K,Na)NbO3 (KNN) materials with enhanced piezoelectric performance. The proposed framework integrates machine learning with feature engineering, surrogate-based optimisation, and experimentation in an active learning loop. Using feature engineering techniques, we demonstrated that the piezoelectric coefficient d33 of KNN materials can be predicted based on a set of elemental and atomic properties. We evaluated six machine learning models and found that support vector regression with a radial basis function kernel achieved high accuracy in predicting the d33 values of KNN ceramics. After three iterations of experimentation and optimisation, we identified an optimal composition with a relatively high d33 of ∼353 pC/N from thousands of possible compositions using a pure exploitation strategy. This study demonstrates an efficient and systematic approach to the composition design of KNN-based piezoceramics, which can be applied to investigate the diverse functional properties of other materials.

Energy-Harvesting Device Based on Lead-Free Perovskite

This research investigates the solid-state synthesis of lead-free (K, Na)0.5NbO3 ceramics to improve the performance of triboelectric nanogenerators (TENGs) for energy-harvesting applications. The TENGs have developed as potential devices for converting mechanical energy into electrical energy. However, traditional TENG materials frequently include lead, which raises environmental and health problems. To overcome this issue, lead-free ceramics were examined as alternative materials with superior properties. In this work, a TENG was fabricated using potassium sodium niobate (KNN) ceramics as one triboelectric layer, Kapton as the other triboelectric layer, and a flexible substrate. The aim was to create TENGs with improved performance and environmental sustainability. The output performance of the TENG was estimated to be 70 V and 1100 nA. The TENG was further used to charge capacitors, light up an LED, and harvest energy from various body motions.

Exploring the application of piezoelectric ceramics in bone regeneration.

Piezoelectric ceramics are piezoelectric materials with polycrystalline structure and have been widely used in many fields such as medical imaging and sound sensors. As knowledge about this kind of material develops, researchers find piezoelectric ceramics possess favorable piezoelectricity, biocompatibility, mechanical properties, porous structure and antibacterial effect and endeavor to apply piezoelectric ceramics to the field of bone tissue engineering. However, clinically no piezoelectric ceramics have been exercised so far. Therefore, in this paper we present a comprehensive review of the research and development of various piezoelectric ceramics including barium titanate, potassium sodium niobate and zinc oxide ceramics and aims to explore the application of piezoelectric ceramics in bone regeneration by providing a detailed overview of the current knowledge and research of piezoelectric ceramics in bone tissue regeneration.

Ultrahigh Electrobending Deformation in Lead-Free Piezoelectric Ceramics via Defect Concentration Gradient Design.

Recent breakthroughs in defect-engineered lead-free piezoelectric ceramics have reported remarkable electrostrain values, surpassing the limit of lattice distortion. This has aroused wide concern on bending deformation and the associated underlying mechanism. Herein, via designing lead-free piezoelectric ceramics with varying volatilization characteristics, it is uncovered that the ultrahigh electrobending deformation is primarily attributed to a large strain gradient induced by unevenly distributed defect dipoles. In 0.5 mm thick Sr/Sn co-doped potassium sodium niobate ceramics featuring volatile K/Na elements, the inherent bipolar electrostrain value can reach 0.3% at 20kV cm-1 due to the existence of defect dipoles, while the gradient distribution of defect dipole generates significant bending displacement, amplifying apparent electrostrain value to 1.1%. Notably, nonvolatile Ba0.99TiO2.99 ceramic with homogeneous defect dipole distribution does not present electrobending. Of particular interest is that the electrobending phenomenon can be observed through introducing a defect dipole gradient into barium titanate ceramic. A monolayer ceramic with defect dipole gradient can generate large tip displacement (±1.5mm) in cantilever structure, demonstrating its promising potential in precise positioning. This study delves into the underlying mechanism driving electrobending deformation and its impact on the apparent electrostrain measurement in defect-engineered piezoelectric ceramics, providing fresh perspectives for the development of piezoelectric bending actuators.

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.

Experimental determination of electrophoretic deposition parameters and electrical characterization for K 0.5 Na 0.5 NbO3 perovskite thick films for energy harvesting applications

Globally, depleting non-renewable energy resources and environmental pollution are significant challenges. Much research is ongoing on perovskite coatings as a potential replacement. In this work, potassium sodium niobate (KNN) ceramics are fabricated by solid-state method, calcined at ∼850 °C, and electrophoreticcally deposited (EPD) on Ni-substrate uniquely then, sintered at high temperatures ∼1070–1120 °C. The X-ray diffraction and FTIR confirmed the development of a pure KNN perovskite structure and metallic bond groups (-O-Nb-O) present respectively. An increase in the sintering temperature resulted in the pronounced peaks observed in KNN ceramics, confirmed by Raman spectroscopy, and easily observed in SEM having “square” and “circular” morphology with grain growth. The coating thickness was measured around 18–116 μm and increasing deposition rate (0.084–0.337 μm/s) was calculated. The coating roughness (∼813 nm) was confirmed by atomic force microscopy. Complex impedance spectroscopic (CIS) analysis confirmed the high dielectric constant (∼4789) with a high transformation and curie temperature (TO→T ∼ 280 °C & TC ∼ 480 °C), respectively. The increasing conductivity (≥830 μS/m) at higher frequency and temperatures agree with the hopping conduction mechanism which confirmed the negative temperature coefficient of resistance (NTCR). The work holds great significance in sensors, actuators, spintronics, and energy harvesting applications.

Ultrafast charge‐discharge and enhanced energy storage properties of lead‐free K0.5Na0.5NbO3‐based ceramics

AbstractFor dielectric capacitors in pulsed power systems, ultrafast charge‐discharge rates and good energy storage performances are essential. The relatively low efficiency η and the low energy density of potassium sodium niobate ceramics will restrict their applications. In this work, a local distortion of the crystal structure of ceramics is made by introducing the Bi and Ce ions, promoting the growth of polar nano‐regions, resulting in more obvious relaxation behavior and lower remnant polarization Pr. The average grain size is reduced, further increasing of breakdown strength. Eventually, fine comprehensive energy storage performances and good mechanical properties are simultaneously obtained. Enhanced recoverable energy storage density Wrec (∼5.30 J/cm3) and a high energy storage efficiency η (∼76.81%) are achieved in 0.970(K0.5Na0.5)NbO3‐0.030CeBiO3 (KNN‐0.030CB) ceramics with an ultrafast discharge rate t0.9 (31 ns) and a high current density (1008.5 A/cm2). All of these results indicate that this work provides a resultful way to design excellent comprehensive properties for advanced energy storage materials.

The effect of ZnO and MnO2 as sintering aids in the preparation of potassium sodium niobate ceramics and electrical characterizations

Potassium sodium niobate (KNN) is an environmentally compatible piezoelectric material for substituting harmful lead-based ceramics. KNN-based ceramics have excellent piezoelectric properties with high Curie temperature. But, KNN faces difficulties during the processing like volatilization of alkali elements, chemical inhomogeneity, low densification, etc. The objective of this research is to investigate the impact of certain metal oxides additions like ZnO and MnO2 as sintering aids to solve the problems of the preparation and hence study the structural and electric properties of K0.5N0.5NbO3 (KNN) ceramics. ZnO and MnO2 added potassium sodium niobate, K0.5N0.5NbO3 was prepared by using the ceramic method. The prepared samples were sintered at 1000 °C for 2h conventionally. The structural properties of the ceramics have been analyzed by using X-Ray Diffractometer. The study demonstrates the formation of the orthorhombic-symmetric perovskite phase in all the prepared samples. The microstructural behavior of the ceramics has been characterized by techniques such as scanning electron microscopy (SEM) and compositional properties were studied by energy dispersive x-ray (EDAX). The effects of metal oxide additions on the electronic properties such as dielectric constant, dielectric loss, impedance properties, Nyquist plot, etc., were studied. The results have been analyzed and discussed in the paper.

Superior Electromechanical Compatibility in Lead-Free Piezoceramics with Mobile Transition-Metal Defects.

Donor and acceptor ions serving as extrinsic defects in piezoelectrics are mostly used to improve the performance merits to satisfy the industrial application. However, the conventional doping strategy is unable to overcome the inherent trade-off between the piezoelectric coefficient (d33) and mechanical quality factor (Qm). Herein, inspired by the valence state variation observed in manganese oxides during sintering, this study focuses on manipulating intrinsic oxygen vacancies and extrinsic manganese defects in potassium sodium niobate (KNN) ceramics via heat treatment. The annealing process results in a simultaneous improvement in both d33 (20%) and Qm (80%), leading to comparable performance with commercial PZT-5A ceramics and enabling their application in atomizer components. Moreover, the mechanism of manganese occupation and diffusion is proposed by an extended X-ray absorption fine structure and density functional theory analysis. The improved electromechanical performance in the annealed KNN ceramic is associated with the optimized redistribution of acceptor and donor manganese defects, which is facilitated by the recombination of oxygen vacancies. This work breaks longstanding obstacles in comprehending the existing forms of manganese in KNN and offers potential in popularizing KNN-based piezoceramics to replace traditional PZT lead-based counterparts in the industrial market.

Grain Boundary Diffusion Hardening in Potassium Sodium Niobate‐Based Ceramics with Full Gradient Composition and High Piezoelectricity

AbstractReducing mechanical losses and suppressing self‐heating are critical characteristics for high‐power piezoelectric applications. For environmentally friendly Pb‐free piezoelectric ceramics, traditional acceptor doping or annealing treatments have successfully improved the mechanical quality factor (Qm) based on a ceramic matrix with a poor piezoelectric coefficient (d33<100 pC/N). Nevertheless, a ceramic with high Qm and d33 values has not been reported owing to the inverse relationship between Qm and d33. Herein, a novel hardening method called grain boundary diffusion is used to develop Pb‐free potassium sodium niobate ceramics, where Qm increased by more than two‐fold (from 51 to 132) and a high d33 value (d33 = 360 pC/N) is maintained. Significantly, d33 retained 98% of its initial value after 180 days, exhibiting improved aging stability. The established properties are associated with the formation of the core‐shell microstructure and the full gradient composition distribution using structural characterizations and phase‐field simulations, where the core maintains a high d33 and the shell provides a hardening effect. The novel hardening effect in piezoelectric materials, known as grain boundary diffusion hardening, highlights the enhancement of the mechanical quality factor with high piezoelectricity, providing a new paradigm for the design of functional materials.

Effect of heterovalent-ion doping and oxygen-vacancy regulation on piezoelectric properties of KNN based lead-free ceramics

Next generation advanced piezoelectric transducers significantly rely on lead-free piezoelectric ceramics. Previous investigations have indicated that defect engineering by acceptor doping is a preferable approach to customize piezoelectric materials, but this method leads to a trade-off between d33 and the electromechanical qualities (Qm, kp, etc.), which make the collaborate modulation to be a great challenge. In this work, a novel synergistic modulation combing heterovalent-ion donor doping and oxygen-vacancy regulation is proposed to achieving preferably balanced piezoelectric properties. Herein, (K0.5Na0.5)1-xCaxNbO3 ceramics (abbreviated as 100xKNCN) are prepared based on a solid-state reaction method, and the effects of electromechanical properties of potassium sodium niobate (KNN) ceramics are regulated by defect dipoles and oxygen vacancies. The results elucidate that an appropriate quantity of Ca ion doping could construct a rhombohedral-tetragonal (R–O) phase boundary, which is beneficial to the improvement of d33 and Qm. Furthermore, a preferably balance of electromechanical qualities and piezoelectric coefficient is realized by annealing the sample in N2 atmosphere (2KNCN/N2). Compared with 2KNCN, the d33 and Qm of 2KNCN/N2 increase by approximately 30% and 41%, respectively. This work is expected to provide an effective paradigm to develop defect engineering and make it a promising candidate for industrial piezoelectric application.

Cold sintering assisted two-step sintering of potassium sodium niobate (KNN) ceramics

Potassium sodium niobate (KNN) ceramics were densified using a multiple-stage sintering process in which initially applied cold sintering process (CSP) was followed by the solid-state sintering between 1100 and 1120 °C. Comparative assessments demonstrated that multi-step sintered samples yielded better properties than conventionally sintering ones. The highest relative density (94.7%) and the best electrical properties were obtained from the sample subjected to cold sintering at 120 °C/1 h using 5 wt% deionized water subsequently heat-treated at 1120 °C/2 h, resulting in a monolithic KNN ceramic having a piezoelectric coefficient of 120 pC/N.

KNN–Eu transparent ferroelectrics: Local structure and luminescent property

AbstractDiffer from the rapid development of piezoelectricity in potassium sodium niobate (KNN) ceramics, the progress of photoluminescence in transparent KNN ferroelectric ceramics remains stagnant. Herein, europium (Eu)‐doped KNN ceramics have been prepared to investigate its local structure and optical–electrical multi‐functionality. Both enhanced piezoelectricity in ceramics with a bimodal distribution of grain size and improved luminescent property in ceramics with refined grain size can be achieved by adjusting the content of Eu. The addition of Eu can destroy long‐range ferroelectric orders, leading to the formation of pseudo‐cubic phase and polar nanoregions (PNRs). The highly activated PNRs promoted electric field‐induced domain switching and nearly reversible piezo/ferroelectric properties. First‐principles calculations show that Eu substitution will lead to local inhomogeneous chemical bond environment, affecting the local electric/elastic fields and crystal fields, and then benefiting to the luminescence behavior, including both the intensity and lifetime. We believe that this work can benefit to the development of KNN transparent luminescent ceramics and the light‐emitting devices.

ДИЭЛЕКТРИЧЕСКИЕ СВОЙСТВА КЕРАМИК НИОБАТА ТИТАНАТА НАТРИЯ КАЛИЯ

The paper considers the preparation of potassium sodium niobate ceramics doped with titanium in an amount of 5 mol. %. The structure and dielectric properties were investigated in the temperature range 30–650 °C. It is shown that acceptor doping leads to a decrease in the grain size. Violation of stoichiometry in the anionic sublattice contributes to a decrease in the relaxation time of thermal ionic polarization compared to the case of nonstoichiometry in the cationic sublattice.

Characterization of UV Light Curable Piezoelectric 0-0-3 Composites Filled with Lead-Free Ceramics and Conductive Nanoparticles

Lead-free piezoelectric materials are essential for our healthy future but offer lower performance than lead-based materials. Different material combinations are explored to improve the performance of lead-free materials. By filling the UV light curable photopolymer resin with 30 vol.% lead-free piezoelectric ceramics and with up to 0.4 wt.% conductive nanofillers, thin and flexible piezoelectric 0-0-3 composites are formed. Two particle sizes of Potassium Sodium Niobate (KNN) and Barium Titanate (BTO) ceramics were used with four conductive nanofillers: Graphene Nanoplatelets (GNPs), Multi-Walled Carbon Nanotubes (MWCNTs), and two types of Graphene Oxide (GO). Resulting high viscosity suspensions are tape-cast in a mold as thin layers and subsequently exposing them to UV light, piezoelectric composite sensors are formed in 80 s. Even low nanofiller concentrations increase relative permittivities, however, they strongly reduce curing depth and increase undesirable dielectric losses. Non-homogeneous dispersion of nanofillers is observed. In total, 36 different compositions were mixed and characterized. Only six selected material compositions were investigated further by measuring mechanical, dielectric, and piezoelectric properties. Results show KNN composite performance as piezoelectric sensors is almost six times higher than BTO composite performance.

Mechanical and electrical properties of sodium potassium niobate ceramic coating by plasma spraying

Potassium sodium niobate ceramics are environmentally friendly piezoelectric ceramics with excellent electrical properties. It is the most promising green piezoelectric ceramic for current applications. Currently, ceramics are needed in the form of thin films or coatings for brakes, sensors, etc. Most of the current ceramic films are prepared by physical vapor deposition and chemical vapor deposition. However, the ceramic layers prepared by the above methods are thin. The thickness of the ceramic layer has a large influence on its mechanical and electrical properties. The coatings prepared by thermal spraying are thicker, but there is no in-depth study about the relationship between the coating thickness and the mechanical and electrical properties of the coating. In this article, four different thicknesses of coatings were prepared by plasma spraying technology, and the relationship between the mechanical and electrical properties of the coatings and the thickness was studied and discussed. The results show that the coating microhardness and residual compressive stress values reach the maximum and the dielectric and ferroelectric properties are optimal when the coating thickness reaches 300 μm. The study of the connection between coating thickness and coating mechanical and electrical properties provides a theoretical study for the application of the coating in practice.

Hardening Effect in Lead-Free KNN-Based Piezoelectric Ceramics with CuO Doping.

As the most promising lead-free piezoelectric ceramics to replace lead zirconate titanate (PZT) ceramics, potassium sodium niobate (KNN) ceramics have been widely studied for their application prospects in various electronic devices. Increasing Qm while maintaining a high piezoelectric activity is quite important for piezoelectric ceramics applied in ultrasonic devices. A KNN-based ceramic with high d33 and Qm is prepared by a conventional solid-state technique to construct polycrystalline phase boundaries and induce defect dipoles. The best overall performance can reach d33 = 260 pC/N, Qm = 210, and TC = 293 °C. The temperature dependence of the relevant parameters is tested, where Qm increases but d33 decreases with the rise of temperature accompanied by escaping ferroelectric boundary, which shows that the polarization rotation plays an important role in the two parameters. The hardening effect of KNN-based ceramics with CuO doping is further studied by first-principles calculations, demonstrating that the Cu doping strongly disturbs the ferroelectric order, but the formation of defect dipoles could stabilize the ferroelectric order. It is illustrated that defect dipoles always find their ground state at the site near the domain walls and the oriented defect dipoles hinder the polarization rotation severely, confirming the role of the defect dipoles in KNN-based materials.

Coupling effects of the A-site ions on high-performance potassium sodium niobate ceramics

• Unveiling the effects of the K/Na ratio on PBE-featured KNN-based ceramics from multiscale view. • Observing the local stress heterogeneity in Na + rich side and the local polar heterogeneity in K + side. • Unraveling the role of the coupling between the local stress heterogeneity and the polar heterogeneity in piezoelectric properties and the temperature stability. Although vast efforts have been given to the phase boundary engineering (PBE) of potassium sodium niobate (KNN) ceramics by using chemical dopants, the inherent issues like the K/Na ratio were not paid enough attention, hindering the further understanding of physical mechanisms. Herein, we investigated the effect of the K/Na ratio on PBE-featured KNN-based ceramics. The K/Na ratio significantly influences the local A-site environment and thereby alters mesoscopic ferroelectric domains and macroscopic structure and performance. A much higher Na + content results in the local stress heterogeneity, while a much higher K + content brings in the local polar heterogeneity. Due to the appropriate coupling between the local stress and the polar heterogeneity, piezoelectric properties and the temperature stability of electro-strain are optimized on the Na-rich side. Therefore, beyond seeking appropriate chemical dopants, elaborately tailoring the K/Na ratio is also important for further improving the piezoelectric properties of PBE-featured KNN-based ceramics.