Potassium Sodium Niobate Research Articles

Reversible Multimode Luminescence Modulations in Photochromic-Translucent Yb3+/Eu3+ Codoped K0.5Na0.5NbO3 Ceramics.

Luminescent tunable materials have promising application potential in optical switches, optical information storage, and so on. Although europium (Eu) is a good downconversion red luminescent rare earth element, there are few studies on the upconversion luminescence and photochromism of Eu-doped potassium sodium niobate (KNN) ferroelectrics. In this paper, Eu3+ and Yb3+ codoped KNN translucent ferroelectric ceramics were synthesized and the effect of Yb3+ content on the luminescence and photochromism is studied. Both the up- and downconversion luminescence intensity and decay rate before and after photochromism can be well controlled by Yb3+ content. That is, an upconversion luminescent translucent ceramic that can be completely discolored by 405 nm light illumination for 10 s was obtained. The luminescence modulations are closely related to the evolution of oxygen vacancy and crystal field around the luminescence center, which can be verified by the illumination-induced electron paramagnetic resonance (EPR) signal and local piezoresponse switching behavior variation as well as the discovery of energy level splitting and spectral line shift. We believe that this work shows a paradigm for designing high-performance reversible multimode luminescence modulation ferroelectric ceramics.

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.

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.

Design, Fabrication, and Characterization of High-Performance PMUT Arrays Based on Potassium Sodium Niobate

Design, Fabrication, and Characterization of High-Performance PMUT Arrays Based on Potassium Sodium Niobate

Observing the in-situ formation of the lead-free piezoceramic potassium sodium niobate (KNN) with SAED

Observing the in-situ formation of the lead-free piezoceramic potassium sodium niobate (KNN) with SAED

Deciphering the in situ phonon evolution of potassium sodium niobate under varying temperature and electric fields.

The application of in situ Raman spectroscopy under multiple fields is widely recognized as an effective approach for investigating the physical mechanism of phase transitions in ferroelectrics, because it can directly provide the detailed information about the vibration evolution of various phonon modes within lattices, such as bond stretching and rotation. Based on this technique, our work aims to thoroughly probe the dynamics of phase transitions in traditional ferroelectric potassium sodium niobate [(K,Na)NbO3, KNN] under external fields, by analyzing the in situ dependence of wavenumber and intensity of phonon modes under the varying temperature and electric fields. The results indicate that different vibration modes respectively relating to the A-site ions and NbO6 octahedra in KNN exhibit distinct and abrupt distortion behavior during the orthorhombic-tetragonal and tetragonal-cubic transitions. Moreover, a certain degree of distortion can still be observed in the cubic phase above the Curie temperature. With an applied electric field, KNN presents quite different electrostriction in orthorhombic and tetragonal phases. Particularly, more than one kind of phonon mode undergoes non-linear variations under the varying electric fields, accompanied by the mutations at some fixed fields. These findings will be conducive to further understanding the phase transition mechanism in KNN from the perspective of phonon evolution. Simultaneously, it will also give crucial guidance for the design and development of KNN-based ferroelectrics as well as functional devices.

Lead‐Free (K, Na)NbO3 Piezocatalyst with Superior Piezocatalysis and Large‐Scale Production

AbstractAlthough piezocatalysis has achieved preliminary achievements in environmental remediation and biomedical applications, large‐scale fabrication of piezocatalysts with high degradation efficiency and low cost remains challenging. In this work, a new and easy strategy to solve this challenge is innovatively proposed, that is, ceramic‐powder‐driven boosted polarization intensity, and validated the strategy is by examining potassium sodium niobate ((K, Na)NbO3, KNN) ferroelectric. KNN‐3 piezocatalyst, obtained by grinding as‐sintered ceramics into powder, shows a degradation rate (k) as high as 148 × 10−3 min−1 for rhodamine B (RhB) dye and for 31 × 10−3 min−1 for methyl orange (MO) dye, ≈18 times and 66 times than those of previously reported KNN piezocatalysts. The superior piezocatalytic activity is attributed to enhanced polarization intensity, increased oxygen vacancies, and higher charge carrier concentrations. Besides, the KNN‐3 piezocatalyst shows excellent inhibitory effects on Staphylococcus aureus and Escherichia coli strains. Therefore, the proven ceramic preparation technology enables the new strategy to mass produce high‐performance KNN piezocatalysts that hold promise for applications in dye degradation and biomedicine.

Fabrication, Evaluation, and Multiscale Simulation of Piezoelectric Composites Reinforced Using Unidirectional Carbon Fibers for Flexible Motion Sensors.

Piezoelectric composite materials can convert mechanical energy into electrical energy, thus promoting battery-free motion-sensing systems. However, their substandard mechanical performance limits the capability of sensors developed using flexible piezoelectric materials. This study introduces a novel design strategy for preparing high-strength flexible piezoelectric composite materials comprising unidirectional carbon fiber-reinforced potassium sodium niobate (K0.5Na0.5NbO3) nanoparticle-filled epoxy resin (UDCF/KNN-EP). The fibers significantly improve the Young's modulus of UDCF/KNN-EP along the fiber direction, which reaches 282.5MPa. Moreover, the composite exhibits excellent stretchability and piezoelectric response ( ) in the cross-fiber direction under cyclic tensile loading. Multiscale finite element analysis is performed via simulation, which allows theoretical examination of the experimental results and the material's mechanical response mechanism. Finally, UDCF/KNN-EP is seamlessly incorporated into athletic gear and used to measure the impact caused by baseball catching and track footfall patterns. This study harnesses the superior strength of carbon fibers to enhance the durability and dependability of self-powered sensors without compromising flexibility in specific directions.

Multi‐Length Engineering of (K, Na)NbO3 Films for Lead‐Free Piezoelectric Acoustic Sensors with High Sensitivity

AbstractWith increasing concerns about noise pollution, the pursuit of highly dependable piezoelectric acoustic sensors for real‐time noise monitoring has come to the forefront of scientific research. Lead‐based perovskite piezoelectric films, exemplified by lead zirconate titanate Pb(Zr,Ti)O3 (PZT), surpass traditional piezoelectric materials such as ZnO and AlN in their piezoelectric properties, promising substantial advancements in next‐generation acoustic sensor technologies. However, the toxic nature of lead in PZT materials poses formidable environmental and human health risks. In an unprecedented breakthrough, it presents the pioneering development of an environmentally benign lead‐free piezoelectric Micro‐Electro‐Mechanical System (MEMS) acoustic sensor based on potassium sodium niobate (K,Na)NbO3 (KNN) film. High‐quality <001> textured 3 µm‐thick KNN film is successfully integrated into commercially used Si substrate, rendering exceptional piezoelectricity (transverse piezoelectric coefficients e31* of ≈8.5 C m−2) with satisfactory thermal stability. The atomic‐scale Z‐contrast imaging and piezoresponse force microscopy characterizations reveal that the outstanding piezoresponse originates from the local coexistence of multiple phases and the enhancement of extrinsic piezoelectric contributions from in‐plane polarization anisotropy. Finite element simulation is employed to design the triangular cantilever structure and annular diaphragm structure, each corresponding to different operating bandwidths. The resultant MEMS acoustic sensors stand out with outstanding acoustic performance (the high sensitivity and expansive receiving field of view), which are attributed to the microstructural engineering at multi‐length scales for the excellent piezoelectric properties of KNN film. These features enable sensitive acoustic monitoring in various environments, including large‐scale power grids and urban traffic.

Design and application of a flexible nano cardiac sound sensor based on P(VDF-TrFE)/KNN/GR composite piezoelectric film for heart disease diagnosis

The paper proposes a flexible micro-nano composite piezoelectric thin film. This flexible piezoelectric film is fabricated through electrospinning process, utilizing a combination of 12 wt% poly(vinylidene fluoride-co-trifluoroethylene)(P(VDF-TrFE)), 8 wt% potassium sodium niobate (KNN) nanoparticles, and 0.5 wt% graphene (GR). Under cyclic loading, the composite film demonstrates a remarkable increase in open-circuit voltage and short-circuit current, achieving values of 36.1 V and 163.7 uA, respectively. These values are 5.8 times and 3.6 times higher than those observed in the pure P(VDF-TrFE) film. The integration of this piezoelectric film into a wearable flexible heartbeat sensor, coupled with the RepMLP classification model, facilitates heartbeat acquisition and real-time automated diagnosis. After training and validation on a dataset containing 2000 heartbeat samples, the system achieved an accuracy of approximately 99% in two classification of heart sound signals (normal and abnormal). This research substantially enhances the output performance of the piezoelectric film, offering a novel and valuable solution for the application of flexible piezoelectric films in physiological signal detection

Electrospun (K,Na)NbO3 Piezoceramic Fibers for Self‐Powered Tactile Sensing Application

This study investigates the electrical properties of electrospun ceramic fiber mats based on potassium sodium niobate ((K,Na)NbO3;KNN) for potential applications in soft‐robotic tactile sensors. The rheological studies of electrospinning solutions exhibit shear thinning behavior, with a viscosity plateau between shear rates of 1–100 s−1. The thermal decomposition behavior of the KNN samples is analyzed using thermogravimetric analysis; the samples show multistep decomposition processes leading into a phase pure perovskite structure. For the electrospun KNN fiber mats, the electrical characterization reveals ferroelectric hysteresis loops with a high leakage current of ≈270 nA at 20 kV cm−1 and switching current behavior. The ferroelectric results indicate that a full polarization of KNN‐fiber mats is not possible due to their electrical breakdown at high electrical fields. The integration of KNN short fibers into a soft‐bending actuator demonstrates successful tactile sensing capabilities. The experimental findings reported here highlight the potential of electrospun KNN fiber mats for flexible and autonomous device applications in soft robotics.

Piezoelectrically induced augmented functionality of primary cultured hippocampal neurons on electrospun PVDF-(Na, K) NbO3 composite fibers

Owing to the risk of permanent disability of the associated tissue/organ, peripheral nerve injuries present one of the major concerns. As growth and regeneration of axons are sensitive towards electrical activity of substrate, polyvinylidene difluoride (PVDF)−10 vol% sodium potassium niobate (NKN) piezoelectric composite fibers were electrospun and corona poled at 17 kV. Electrospun PVDF-NKN fibrous scaffolds show remarkable increase in the average number of dendrites per neuron and mean soma area of primary cultured hippocampal neurons of embryonic mice which further increases after polarization (∼ 1.3 and 1.6 times of unpoled PVDF, respectively). The developed composite can be suggested as a potential candidate for peripheral nerve regeneration.

Lead-free KNNLT piezoceramic multilayer actuators with Ni electrodes cofired under low oxygen partial pressure

The fabrication of piezoelectric multilayer actuators (MLA) with lead-free piezoceramic materials and excellent performance represents a great challenge in the process of replacing the current family of lead-based actuators. Sintering under low pO2 allows co-firing with base metal electrodes, which is an important step towards competitive multilayer actuator fabrication technologies. We prepared sodium potassium niobate (KNNLT) piezoelectric multilayer actuators with Ni electrodes by sintering at low pO2 of 10−11 atm at 950 °C, followed by reoxidation at 850 °C in 10−6 atm. We demonstrate the impact of the sintering protocol, i.e., sintering temperature Ts and pO2, on the phase composition and continuity of Ni electrodes, and on the actuator performance. We discuss the subtle interplay between sintering conditions, microstructure, reoxidation kinetics and piezoelectric performance. The Ni-MLA exhibits a unipolar strain of 0.74 ‰ at 3 kV/mm, a normalized strain coefficient d33* = 247 p.m./V and a loss of tanδ = 0.041.

Constructing the relationship between microstructure and piezocatalysis in (K, Na)NbO3 lead-free piezocatalyst

Piezocatalysis converts mechanical vibration into chemical energy and holds great potential for wastewater treatment and biomedical applications. Although the influence of microstructure on piezocatalysis is well recognized, its relationship has been rarely investigated in potassium sodium niobate ((K, Na)NbO3, KNN), an emerging lead-free and eco-friendly piezocatalyst. In this study, we modified the synthesis conditions of (K0.48Na0.52)NbO3-0.3 %Fe2O3 (KNN-Fe) material to produce KNN-Fe piezocatalysts with different microstructure characteristics. We then examined the relationship between microstructure and piezocatalysis by assessing the degradation of Rhodamine B (RhB) and methyl orange (MO) dyes. The KNN-Fe piezocatalyst with an 8 h-sand-ground shows the reaction rate constant (k) values of 79 × 10−3 min−1 and 27.12 × 10−3 min−1 for the degradation of RhB and MO, respectively. These values are 16 % and 303 % higher than those of the sand-ground-0 h sample. The enhanced piezocatalysis of the sand-ground-8 h sample stems from the increased specific surface area and oxygen vacancies, enhanced separation of electron-hole pairs, and higher carrier concentration. This study not only elucidates the relationship between microstructure and piezocatalysis in KNN materials but also suggests a potential approach for enhancing piezocatalytic activity.

Revealing the mechanism of competing A‐site doping ions in (K, Na)NbO3‐based ceramics

AbstractAlthough past studies have shown a competitive relationship between bismuth ion (Bi3+) and rare earth ions in potassium sodium niobate {(K, Na)NbO3, KNN}‐based ceramics, a comprehensive investigation of this competition has been relatively scarce. Herein, we conducted an in‐depth exploration of this competition by substituting Bi3+ with praseodymium ions (Pr3+) in KNN‐based ceramics possessing high piezoelectric properties. The substitution of Bi3+ with Pr3+ results in a decrease in the extent of multi‐phase coexistence at room temperature, an increase in domain size and grain size, and the enhancement of ferroelectricity. However, it also leads to a deterioration in piezoelectricity. Through a combination of experimental findings and first‐principles calculations, we analyzed the alterations in phase structure, ferroelectric domains, and electrical properties, attributing these changes to the competitive nature of Bi‐O and Pr‐O bonds with their distinct ionic/covalent characteristics. Consequently, this study not only unveils the underlying physical mechanism behind the competition between Bi3+ and Pr3+ ions in KNN‐based piezoceramics but also presents a novel approach to tailor the phase transition temperature, thereby facilitating the overall performance improvement of KNN‐based ceramics.

Enhanced optical and energy storage properties of K0.5Na0.5NbO3 lead-free ceramics by doping Bi(Sr0.5Zr0.5)O3

Transparent relaxation ferroelectric ceramics with excellent transmittance and energy storage density are indispensable for efficient multifunctional coupling. These ceramics have found extensive applications in transparent energy storage electronics, advanced pulsed power capacitors, and optoelectronic multifunctional devices. In this study, we employed a combination of strategies to enhance the optical and electrical properties of ceramics. Specifically, the breakdown field strength of potassium sodium niobate (KNN) was increased by introducing Bi(Sr0.5Zr0.5)O3 (BSZ), which reduced the ceramic grain size. The incorporation of polar nano-micro-regions led to stronger local polarity fluctuations on the nanoscale, effectively minimizing the residual polarization. Furthermore, the forbidden bandwidth of the system was widened to mitigate photoelectron optical energy loss during transition.The newly developed ceramic, (1-x) KNN-xBSZ, exhibited remarkable performance characteristics, including an energy storage density of 4.13 J/cm3, a recoverable energy storage density of 2.95 J/cm3 at a low electric field of 245 kV/cm, and an energy storage efficiency of 84 %. Additionally, at 700 nm, the 0.875KNN-0.125BSZ sample displayed a transmittance of 52 %. Notably, this ceramic demonstrated high power density (PD = 36.76 MW/cm3) and rapid charge/discharge rates (t0.9 = 0.94 μs). Moreover, it exhibited excellent temperature and frequency stability, making it a dependable option for optoelectronic devices utilizing transparent relaxation ferroelectric ceramics.

Enhanced Piezoelectric and Dielectric Properties of Lead Free Textured KNN - Epoxy 0-3 Composites

Lead-free textured potassium sodium niobate, (K0.476, Na0.524) NbO3 (KNN), prepared using templated grain growth method (TGG) is used as the filler for the preparation of textured KNN - Epoxy piezoelectric composites. The composites were prepared for 10, 20, 30, 40, 50 volume percent of the filler particles. The prepared composites were polished, electroded and were poled at the rate of 2kV/mm. Lotgering orientation factor (LOF) of 21% is obtained for particles prepared by templated grain growth method. The piezoelectric charge coefficient (d33), dielectric constant and piezoelectric voltage coefficient (g33) were measured. It has been observed that, there is an increase in the piezoelectric and dielectric properties while increasing the KNN filler percentage. The experimentally obtained piezoelectric and dielectric properties have been analyzed and is fitted using the analytical model proposed by Yamada for 0-3 composites for different volume fractions of the constituents.

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.

Optimizing Output Power Density in Lead-Free Energy-Harvesting Piezoceramics with an Entropy-Increasing Polymorphic Phase Transition Structure.

It is an urgent need to develop lead-free piezoelectric energy harvesters (PEHs) to address the energy dilemma and meet environmental protection requirements. However, the low output power densities limit further promotion of lead-free PEHs for use in daily life. Here, an entropy-increasing strategy is proposed to achieve an increased output power density of 819 μW/cm3 in lead-free potassium sodium niobate (KNN)-based piezoceramics by increasing the configuration entropy and realizing nearly two times the growth compared with low-entropy counterparts. Evolution of the energy-harvesting performance with increasing configuration entropy is demonstrated systematically, and the excellent energy-harvesting properties achieved are attributed to the enhanced lattice distortion, the flexible polarization configuration, and the high-density randomly distributed nanodomains with the entropy-increasing effect. Moreover, excellent vibration fatigue resistance and variable temperature output power characteristics were also realized in the PEH prepared by the proposed entropy-increasing material. The significant enhancement of the comprehensive energy-harvesting performance demonstrates that the construction of KNN-based ceramics with high configuration entropy represents an effective and convenient strategy to enable design of high-performance piezoceramics and thus promotes the development of advanced PEHs.

A multiscale generative model to understand disorder in domain boundaries.

A continuing challenge in atomic resolution microscopy is to identify significant structural motifs and their assembly rules in synthesized materials with limited observations. Here, we propose and validate a simple and effective hybrid generative model capable of predicting unseen domain boundaries in a potassium sodium niobate thin film from only a small number of observations, without expensive first-principles calculations or atomistic simulations of domain growth. Our results demonstrate that complicated domain boundary structures spanning 1 to 100 nanometers can arise from simple interpretable local rules played out probabilistically. We also found previously unobserved, significant, tileable boundary motifs that may affect the piezoelectric response of the material system, and evidence that our system creates domain boundaries with the highest configurational entropy. More broadly, our work shows that simple yet interpretable machine learning models could pave the way to describe and understand the nature and origin of disorder in complex materials, therefore improving functional materials design.