Potassium Sodium Niobate Research Articles

Enhanced comprehensive energy storage properties of lead-free KNN based ceramics through composition optimization strategy

As one of the most potential lead-free dielectric capacitors in pulsed power systems, K0.5Na0.5NbO3 (KNN)-based ceramic possesses comparatively high dielectric breakdown strength (BDS) due to its particular submicron grains. Nonetheless, it is hard to improve both the energy efficiency η and the recoverable energy density Wrec of potassium sodium niobate ceramic at the same time. Herein, a composition optimization strategy is used, Bi(Li0.5Nb0.5)O3 (BLN) as a second component and NaNbO3 (NN) as a third component are introduced into KNN-based ceramic. It is corroborated that BLN content facilitates the growth of polar nano-regions (PNRs), and then strengthens the relaxation behavior, lows the remnant polarization Pr and upgrades the maximum polarization Pmax value of the ceramic. A transition from ferroelectricity to relaxation ferroelectricity occurred and an ultrahigh Wrec of 10.03 J/cm3 with a η of 64.15 % and the BDS of 1140 kV/cm are gained in KNN-0.100BLN-NN ceramic, Wrec of 8.25 J/cm3, η of 71.26 % and the BDS of 840 kV/cm are obtained in KNN-0.075BLN-NN ceramic. Besides, the KNN-0.075BLN-NN ceramic exists not only fine energy storage properties, but also high hardness and good temperature and frequency stability, confirming it’s a feasible material to be applied in pulsed power systems

Terraced (K, Na)NbO3 piezocatalysts with superior H2O2 production

Piezocatalytic hydrogen peroxide (H2O2) production is an emerging and green technology, but complex preparation process of piezocatalyst and low production rate limit its practical application. Herein, we propose a straightforward and efficient strategy, that is, fabricating a novel terraced potassium sodium niobate (KNN-H) by integrating high-energy pendulum ball-milling into the conventional solid-state method, to control the morphology of piezocatalyst and boost its piezocatalytic activities. By exposing a large number of edge sites with higher piezoelectric response and more active sites, KNN-H sample exhibits an extremely high H2O2 production rate of 47 μmol/h, about 35 times higher than that of previously reported potassium niobate piezocatalyst. Besides, KNN-H sample also has good effects on dye degradation and bacterial inhibition. Therefore, our strategy provides a paradigm for large-scale fabrication of high-performance perovskite piezocatalysts.

Energy harvesting properties for potassium-sodium niobate piezoceramics through synergistic effect of phase structure and texturing engineering

In order to address the energy dilemma and meet environmental protection requirements, it is an urgent need to develop lead-free piezoelectric energy harvesters (PEHs). However, the low output power density has seriously hindered the application of lead-free piezoceramics as high efficiency energy harvesters. To solve above question, the combination of phase structure regulation and texturing technique in the K0.5Na0.5NbO3-xBi0.5Na0.5ZrO3-0.5%wtBiFeO3 (KNN-xBNZ) ceramics was adopted in this work. Because of both the Rhombohedral-Orthorhombic-Tetragonal (R-O-T) multiphases coexistence and texturing engineering, an ultrahigh piezoelectric activity quality factor d33×g33 ∼ 18324 ×10-15 m2·N-1 was achieved in the textured KNN-0.05BNZ (T-KNN-0.05BNZ) ceramics, which is about third times higher than that of random KNN-0.05BNZ (R-KNN-0.05BNZ) (d33×g33 ∼ 6672 ×10-15 m2·N-1) ones. A high output power of ∼ 0.32 mW was also obtained in the T-KNN-0.05BNZ ceramics by cantilever beam-based energy harvester devices under the resonance frequency of 75 Hz and matched RL of 1.2 MΩ, suggesting that the T-KNN-0.05BNZ ceramics have a great potential for application in the PEHs devices. This result also reveals that the combination of phase structure regulation and texturing technique is an effective way to achieved a high energy harvesting performances.

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.

Fabrication and in vitro biological properties of hydroxyapatite-sodium potassium niobate-barium titanate piezoelectric bioceramics

The utilization of piezoelectric materials in bone implants is appealing due to the inherent piezoelectric property of natural bone. The intrinsic electrical characteristics of piezoelectric biomaterials enhance antibacterial activities, biocompatibility, and bioactivity properties. This study delves into investigating the antibacterial properties, biocompatibility, and bioactivity of three-component biocomposites: sodium potassium niobate (KNN)-barium titanate (BT)-hydroxyapatite (HA). The combination of sodium potassium niobate and barium titanate, possessing suitable piezoelectric properties, with hydroxyapatite, known for its favorable biological properties, enhances the requisite properties for a bone implant. Among the various compositions studied, the combination comprising 70 wt% of the piezoelectric component (KNN-BT) and 30 wt% hydroxyapatite, labeled as 30HKB, emerged as the most optimal blend in terms of density, morphotropic phase boundary, and other biological tests conducted. Following polarization, the antibacterial efficacy of 30HKB against S. aureus bacteria cells increased by 61 %. Furthermore, the growth and adhesion of MC3T3-E1 osteoblast cells suggest enhanced biocompatibility of the 30HKB composite attributed to surface polarization. The surface charges generated by polarization facilitated the absorption of Ca2+ ions, as well as the interaction of HPO4 - and OH- ions with the precipitated Ca2+ ions, leading to the formation of the CaP layer. Hence, polarized piezoelectric ceramics exhibit heightened bioactivity compared to their non-polarized counterparts.

Spatiotemporal piezoelectric microcapsules for programmable sonodynamic sterilization and wound healing

Hydrogel particles have certain practicability in facilitating wound healing, nowadays endeavors have been devoted to developing particles with architectural construction and controllable cargo release property for infected wound management. Here, inspired by the cocktail treatment, we propose a spatiotemporal piezoelectric microcapsule with potassium sodium niobate (KNN)-encapsulated shell and vascular endothelial growth factor (VEGF)-loaded core (KV-MPs) via microfluidic technology for ultrasound (US)-assisted infected wound treatment. As a biocompatible piezoelectric material, KNN exert piezocatalytic redox and reactive oxygen species (ROS)-generating property under US excitation, contributing to bacterial elimination. With the degradation of the shell, the core exposes and sustainedly releases VEGF for angiogenesis and promoting tissue regeneration. In mice with infected wound, we have demonstrated that the US-excited KV-MPs can effectively fight bacteria and subsequent accelerate wound repair. These results indicated our spatiotemporal piezoelectric microcapsules provide an effective strategy for sonodynamic sterilization meanwhile realize tissue regeneration.

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.

A biodegradable piezoelectric scaffold promotes spinal cord injury nerve regeneration

Neural repair and regeneration remain one of the greatest challenges in regenerative medicine. The incorporation of intelligent scaffolds with noninvasive in vivo electrical stimulation illustrates considerable potential for tissue repair and regeneration. Nevertheless, the development of biomaterials that possess both biodegradable tissue scaffolds and electrical stimulation capabilities at a high level remains a significant obstacle. In this study, we effectively integrated the organic piezoelectric material poly-L-lactic acid (PLLA) with inorganic piezoelectric nanowires (potassium sodium niobate coated with polydopamine, KNN@PDA) to fabricate PLLA/KNN@PDA piezoelectric composite fibers. These fibers exhibit in-situ electrical stimulation capabilities, rendering them suitable for direct application in living tissues. The PLLA/KNN@PDA piezoelectric composite fibers not only function as biodegradable scaffolds for regenerative tissue engineering and platforms for in-situ electrical stimulation to enhance dorsal root ganglion axon growth, proliferation, and neuronal differentiation but also serve as versatile scaffolds for broader tissue engineering applications. In the complete spinal cord transection rat model, the piezoelectric scaffold enabled the recovery of rat motor function, indicating its significant ability to promote tissue formation and regeneration. Therefore, combining biodegradable piezoelectric tissue scaffolds with in situ electrical stimulation has significant therapeutic advantages for spinal cord injury repair and may be extended to other damaged tissues regeneration.

Molded, Solid-State Biomolecular Assemblies with Programmable Electromechanical Properties.

Piezoelectric and ferroelectric technologies are currently dominated by perovskite-based ceramics, not only due to their impressive figures of merit, but due to their versatility in size and shape. This allows the dimensions of, for example, lead zirconium titanate and potassium sodium niobate, to be tailored to the needs of thousands of applications across the automotive, medical device, and consumer electronics industries. In this Letter, we significantly advance the performance and customization of biomolecular crystal (nontoxic, biocompatible amino acids, viz., trans-4-hydroxy-L-proline, L-alanine, hydrates of L-arginine and L-asparagine, and γ-glycine) assemblies by growing them as molded, substrate-free piezoelectric elements. This methodology allows for electromechanical properties to be embedded in these assemblies by fine-tuning the chemistry of the biomolecules and thus the functional properties of the single crystal space group. Here, we report the piezoelectric, mechanical, thermal, and structural properties of these amino acid-based polycrystalline actuators. This versatile, low-cost, low-temperature growth method opens up the path to phase in biomolecular piezoelectrics as high-performance, eco-friendly alternatives to ceramics.

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.

KNN composite ceramics with superior pyroelectric performance for self-powered thermal detector

The thermal detector based on pyroelectric effect has attracted widespread attention due to its self-powering and rapid response. Although phase boundary engineered lead-free potassium sodium niobate [K0.5Na0.5NbO3, KNN] based ferroelectrics exhibit promising for pyroelectric sensor application, the high dielectric constants (εr) of these materials significantly constrain their pyroelectric figures of merit (FOMs), owing to the inverse correlation between FOMs and εr. To address this problem, we innovatively introduce perovskite bismuth sodium titanate [Bi0.5Na0.5TiO3, BNT] with low εr and high pyroelectric coefficient as the second phase to construct a KNN/BNT composite. The introduction of BNT can not only remain the high pyroelectric coefficient (p=7.12 × 10−4 C m−2 K−1) of KNN matrix, but also result in superior FOMs (Fv increased by 74 %), outperforming previous KNN-based pyroelectric ceramics. The excellent pyroelectric performance originates from the unique composite microstructure with compositional heterogeneity. That is, both the low εr BNT enriched phase and refined grain size as well as the promoted vibration of Nb–O octahedron contribute to the superior pyroelectric performance. A self-powered thermal detector with great thermal response has been developed, which also exhibits potential for detecting ultraviolet energy and infrared radiation.

In situ observation of ferroelectric domain evolution of (K,Na)NbO3 single crystals during heating

Since the spontaneous polarization and domain switching is closely related with the physical properties of ferroelectric materials, significant research efforts have been carried out to understand domain switching under external fields. However, investigations on the evolution of ferroelectric domains under thermal fields have comparatively been limited. To elucidate the thermal stability of strain and high pyroelectric coefficient observed in potassium sodium niobate (KNN) single crystals, we conducted in situ TEM studies with heating. Our findings reveal that the strain thermal stability originates from the thermal stability of ferroelectric domains. The nucleation of domain configurations of the tetragonal phase from the orthorhombic phase enhances the pyroelectric effect during the phase transition. Furthermore, near the Curie temperature, we identified an intermediate state exhibiting a labyrinth domain configuration between the cubic and tetragonal phases. Our investigation elucidates the underlying mechanisms behind the thermal properties of the material and advances the understanding of the thermal response of ferroelectric domains.

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.

Effect of different donor dopants on the seed-free solid-state crystal growth of potassium sodium niobate

Seed-free solid-state crystal growth (SSCG) is a developing technique to produce lead-free potassium sodium niobate (KNN) single crystals with the advantage of expeditious growth rates. The fundamental mechanism for seed-free SSCG is abnormal grain growth, which can be promoted through the inclusion of a precise concentration of an A-site donor dopant in KNN. To date, Ba2+ and Bi3+ have been utilised to grow centimetre-sized KNN single crystals with piezoelectric properties equivalent to traditional melt growth techniques. This research explores a broad range of potential donor dopants in (K0.5Na0.5Li0.006Dx)NbO3 (where D = Ba2+, Ca2+, Sr2+, Pb2+, Bi3+, La3+, Ce3+,4+ and Pr3+,4+) to determine disparities in abnormal grain growth behaviour and the critical parameters that enable substantial single crystal growth. The incorporation of different donor dopants influences the grain growth behaviour, single crystal sizes and preferential crystallographic orientations. This inspires future research to explore different compositions and techniques to improve the KNN crystal sizes and piezoelectric properties and addressing other challenges. These efforts are essential to improve the maturity of seed-free SSCG, making it industrially viable and a genuine alternative to costly single crystal growth techniques.

Thermal and electromechanical performance in BaSnO3-modified potassium sodium niobate piezoceramics via two-step sintering

In view of industrial applications requiring high piezoelectric activity, KNN-based ceramics face two key constraints: insufficient density and temperature sensitivity. To address these challenges, this study first introduces BaSnO3 and employs two-step sintering method (TSS) for fabrication, thereby synthesizing ternary 0.975K0.5Na0.5NbO3-0.025Bi0.5K0.5TiO3-xBaSnO3 (KNN-1000xBaSn; x = 0, 0.3 %, 0.6 % and 0.9 %) with superior piezoelectricity (d33 = 217–257 pC/N; d33* = 265–330 pm/V; S = 0.16–0.21 %), high Curie temperature (TC = 325–349 °C) and densification (4.3–4.5 g/cm3; relatively density ∼96 %). In one respect, the TSS allows minimal volatilization of alkali metals while promoting grain homogenization. In another respect, the introduction of BaSnO3 enhances the mobility of domain walls, meanwhile fosters diffuse phase transitions (DPT) and widens dielectric peaks without significantly impairing TC. Moreover, the KNN–6BaSn obtain not only reinforced d33 (256 pC/N) with high TC (325 °C) and ε′ (1016), but also fatigue resistance and extreme-temperature endurance with excellent d33* (445 pm/V at 90 °C; 300 pm/V at 180 °C). This work provides a resultful dual-strategy for the emergence of lead-free piezoelectric products.

Modified Re‐Entrant‐Like (K, Na)NbO3‐Based Relaxors with Superior Electrostrain Properties

AbstractPiezoceramics with large strain output, low hysteresis, and wide operation temperature are indispensable for the high‐end displacement control. Unfortunately, requiring these merits simultaneously remains a long‐standing challenge for lead‐free piezoceramics promising for replacing lead‐based ones. Herein a new strategy to resolve this challenge by developing modified re‐entrant‐like potassium sodium niobate ((K, Na)NbO3, KNN) relaxors is presented. Multi‐scale structural analysis reveals the presence of the significant local disorder, nano‐sized multi‐phase coexistence, and ultra‐fine grains, which facilitate the polarization rotation, effectively eliminate non‐180° domains, and erase polymorphic phase transition features in re‐entrant‐like KNN relaxors. Consequently, a combination of large strain (≈0.19%), ultra‐low hysteresis (<7%), high electrostriction coefficient (Q33 = 0.049 m4 C−2), and benign temperature stability (i.e., strain varies less than 10.6% within 30–120 °C) is realized, superior to other lead‐free relaxors. Therefore, this strategy provides a novel paradigm for designing high‐performance lead‐free piezoceramics used for high‐precision actuators.

Study the Structural, Electrical and Ferroelectric behaviour of Lead-Free Sodium Potassium Niobate (KNN) Ceramics in View of Energy Storage Capacity

Study the Structural, Electrical and Ferroelectric behaviour of Lead-Free Sodium Potassium Niobate (KNN) Ceramics in View of Energy Storage Capacity

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.

An implantable piezoelectric ultrasound stimulator (ImPULS) for deep brain activation

Precise neurostimulation can revolutionize therapies for neurological disorders. Electrode-based stimulation devices face challenges in achieving precise and consistent targeting due to the immune response and the limited penetration of electrical fields. Ultrasound can aid in energy propagation, but transcranial ultrasound stimulation in the deep brain has limited spatial resolution caused by bone and tissue scattering. Here, we report an implantable piezoelectric ultrasound stimulator (ImPULS) that generates an ultrasonic focal pressure of 100 kPa to modulate the activity of neurons. ImPULS is a fully-encapsulated, flexible piezoelectric micromachined ultrasound transducer that incorporates a biocompatible piezoceramic, potassium sodium niobate [(K,Na)NbO3]. The absence of electrochemically active elements poses a new strategy for achieving long-term stability. We demonstrated that ImPULS can i) excite neurons in a mouse hippocampal slice ex vivo, ii) activate cells in the hippocampus of an anesthetized mouse to induce expression of activity-dependent gene c-Fos, and iii) stimulate dopaminergic neurons in the substantia nigra pars compacta to elicit time-locked modulation of nigrostriatal dopamine release. This work introduces a non-genetic ultrasound platform for spatially-localized neural stimulation and exploration of basic functions in the deep brain.