NaNbO3 Research Articles

ProtonationDriven Polarization Retention Failure in Nano-Columnar Lead-Free Ferroelectric Thin Films.

Understanding microscopic mechanisms of polarization retention characteristics in ferroelectric thin films is of great significance for exploring unusual physical phenomena inaccessible in the bulk counterparts and for realizing thin-film-based functional electronic devices. Perovskite (K,Na)NbO3 is an excellent class of lead-free ferroelectric oxides attracting tremendous interest thanks to its potential applications to nonvolatile memory and eco-friendly energy harvester/storage. Nonetheless, in-depth investigation of ferroelectric properties of (K,Na)NbO3 films and the following developments of nano-devices are limited due to challenging thin-film fabrication associated with nonstoichiometry by volatile K and Na atoms. Herein, ferroelectric (K,Na)NbO3 films of which the atomic-level geometrical structures strongly depend on thickness-dependent strain relaxation are epitaxially grown. Nanopillar crystal structures are identified in fully relaxed (K,Na)NbO3 films to the bulk states representing a continuous reduction of switchable polarization under air environments, that is, polarization retention failures. Protonation by water dissociation is responsible for the humidity-induced retention loss in nano-columnar (K,Na)NbO3 films. The protonation-driven polarization retention failure originates from domain wall pinning by the accumulation of mobile hydrogen ions at charged domain walls for effective screening of polarization-bound charges. Conceptually, the results will be utilized for rational design to advanced energy materials such as photo-catalysts enabling ferroelectric tuning of water splitting.

Novel NaNbO3-based, ferroelectric ceramics with excellent polarization and electric potential for antibacterial applications

Low surface electric potential (<1V) limits the large-scale commercial application of ferroelectric antibacterial ceramics. We propose a strategy based on charge-balancing doping to enhance polarization and potential in NaNbO3(NN)-based ceramics for disinfection application. The Mg2+ modified NN showed a superior bactericidal effect greater than 80% for 1.5 h and 99.8% for 3 h without heating or ultrasonication, which is superior to other published works. This is mainly due to its excellent surface electric potential of 1.72 V and defect-related discharge current of 141.9 pA compared to NN and Ca2+ modified NN. Ferroelectric properties demonstrated that NN-Mg possesses a lower EC of ∼40 kV/cm and a higher Pr of ∼32 μC/cm2. Furthermore, the combination of XRD, Raman shift, PFM, and permittivity testing suggests that the smaller domain and enhanced ferroelectric properties in NN-Mg originated from amphoteric doping. Finally, simulation results of the electric field distribution indicated that NN-Mg had a stronger attraction or repulsion to bacteria with negatively charged surfaces.

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.

Ultrahigh thermal stability and piezoelectricity of lead-free KNN-based texture piezoceramics

The contradiction between high piezoelectricity and uniquely poor temperature stability generated by polymorphic phase boundary is a huge obstacle to high-performance (K, Na)NbO3 -based ceramics entering the application market as Pb-based substitutes. We possess the phase boundary by mimicking Pb(Zr, Ti)O3’s morphotropic phase boundary structure via the synergistic optimization of diffusion phase boundary and crystal orientation in 0.94(Na0.56K0.44)NbO3−0.03Bi0.5Na0.5ZrO3−0.03(Bi0.5K0.5)HfO3 textured ceramics. As a result, a prominent comprehensive performance is obtained, including giant d33 of 550 ± 30 pC/N and ultrahigh temperature stability (d33 change rate less than 1.2% within 25-150 °C), representing a significant breakthrough in lead-free piezoceramics, even surpassing the Pb-based piezoelectric ceramics. Within the same temperature range, the d33 change rate of the commercial Pb(Zr, Ti)O3−5 ceramics is only about 10%, and more importantly, its d33 (~ 350 pC/N) is much lower than that of the (K, Na)NbO3-based ceramics in this work. This study demonstrates a strategy for constructing the phase boundary with MPB feature, settling the problem of temperature instability in (K, Na)NbO3-based ceramics.

Exploring the mechanisms of enhanced piezoelectric properties in (K,Na)NbO3 single crystals

(K,Na)NbO3 (KNN)-based piezoelectric materials are candidates for replacing Pb-based materials. However, the piezoelectric properties of existing KNN-based single crystals are still inferior to those of Pb-based relaxor ferroelectric single crystals. Moreover, the piezoelectric response mechanism of KNN-based single crystals remains unclear. In this study, (Li,K,Na)(Nb,Sb,Ta)O3:Mn (KNNLST:Mn) single crystals with an excellent piezoelectric coefficient d33 of approximately 778 pC/N were prepared. Systematically studies of intrinsic and extrinsic piezoelectric responses have revealed that the high d33 of KNNLST:Mn single crystals is related to the shear piezoelectric response of a single-domain state and irreversible domain wall motion of the engineering domains. Furthermore, the effect of the orthorhombic (O)-tetragonal (T) phase boundary on intrinsic and extrinsic piezoelectric response is systematically studied, and the impact mechanism is elucidated. The results indicate that a lower dielectric response and elastic constant limit the intrinsic shear piezoelectric response of KNNLST:Mn single crystals, and approaching the O–T phase boundary can enhance both intrinsic and extrinsic piezoelectric responses. This study improves our understanding of the structure-performance relationship in KNN-based single crystals and offers insights for optimizing piezoelectric properties in KNN-based materials.

Growth orientation control in rapid solid-state crystal growth of (K,Na)NbO3 single crystals using plate-like NaNbO3 single crystal particles

The rolling-extended orientation technique and plate-like NaNbO3 (NN) single crystal particles prepared by a single-step molten salt synthesis, both of which have been developed to fabricate (K, Na)NbO3 (KNN) textured ceramics, were utilized to control the growth orientation of KNN single crystals synthesized by a rapid solid-stated crystal growth (RSSCG) method. As the seed crystals, two kinds of NN single crystal particles were synthesized using pure NaCl and KCl-NaCl mixed molten salts. Plate-like KNN single crystals of about 1 cm squares with the upper and lower faces almost parallel to the (100) (001) planes were obtained with a probability exceeding 50% when NN single crystal particles were synthesized from mixed salts and were subsequently thermal-treated again in Na2CO3-NaCl mixed molten salts under appropriate conditions to remove the Bi element, which is known as the suppression factor of the crystal growth. The average crystal growth rate was 0.6–1.2 mm h−1. Controlling the growth orientation of KNN single crystals produced by the SSCG method using seed crystals other than KTaO3 single crystals was successfully accomplished for the first time.

Superior energy storage properties of BiFeO3 doped NaNbO3 antiferroelectric ceramics

NaNbO3 (NN)-based dielectric ceramics for energy storage have garnered significant interest due to their high saturation polarization, low residual polarization, and superior breakdown strength (Eb). However, the low recoverable energy storage density (Wrec) and efficiency (η) significantly limited their practical application. Herein, BiFeO3 (BF) was incorporated into NN to optimize the energy storage performance. The NN-BF ceramics exhibited pronounced antiferroelectric (AFE) relaxor phase, alongside grain size reduction and Eb enhancement, which contributed to a significant increase of Wrec and η. Specially, the optimum Wrec of 4.43 J/cm³ and η of 71.51 % were achieved at the composition of 0.9NN-0.1BF. Besides, stable energy storage performance was maintained over a wide temperature range (20–120 °C). These results highlight the potential of NN-BF relaxor AFE ceramics as promising candidates for high-performance energy storage applications.

Component design for stabilizing P phase in NaNbO3-based ceramics and the energy storage performance

Antiferroelectric (AFE) ceramic dielectrics are widely recognized for their high potential in high-power pulse equipment applications. Lead-free NaNbO3 (NN) antiferroelectric ceramics have emerged as a prominent research topic in the field of energy storage due to their abundant phase structure, affordability, and moderate bandgap. The metastable ferroelectric Q phase results in a square hysteresis loop for NN at room temperature. However, 0.96NaNbO3-0.04 CaZrO3 (NNCZ) exhibits a typical double hysteresis loop at room temperature with the main crystalline phase being the antiferroelectric P phase, which has poor energy storage performance. In this study, Bi0.5Na0.5TiO3 (BNT) is used to optimize the energy storage performance and stabilize the P phase in NNCZ simultaneously. The dielectric constant and temperature-dependence XRD results that from −100 °C to 350 °C, x = 0.05 undergoes a phase transition from AFE P to AFE R and then to PE S. The solid solution of BNT decreased the sintering temperature of NN-based ceramics and decreased average grain size, thereby facilitating domain size reduction and improving the sample's energy storage efficiency from ∼30 % to ∼60 %, with an effective energy storage density reaching 1.51 J/cm3. The above results demonstrate that enhancing energy storage efficiency can be achieved through component design by reducing average grain size.

Enhanced self-driven flexible piezoelectric nanogenerator sensor based on NaNbO3/P(VDF-TrFE) films for security applications

The self-driven flexible piezoelectric sensor has wide application prospects in areas such as health monitoring, human-machine interaction, and warning detection due to its advantages of non-toxicity and high sensitivity. In this study, a composite film of poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] doped with NaNbO3 (NN) was prepared by electrospinning. The highly oriented NN particles promote the formation of P(VDF-TrFE) β phase, reaching a maximum β phase content of 91%. Under mechanical motion at a frequency of approximately 3 Hz, the piezoelectric nanogenerator (PENG) fabricated from the nanofiber membrane achieved a maximum piezoelectric output of 17.3 V and 12 V in the transverse and longitudinal piezoelectric responses, respectively. With an external load of 100 MΩ, the PENG obtained a maximum power density of 0.67 μW/cm². Additionally, the PENG sensor exhibited sensitivity to various human activities and demonstrated high sensitivity and rapid response in monitoring the status of the proposed door lock opening/closing, highlighting its enormous potential in security monitoring applications.

Local defect structure design enhanced energy storage performance in lead-free antiferroelectric ceramics

Antiferroelectrics (AFEs) are ideal candidates in dielectric, electromechanical, and electrothermal applications. NaNbO3 (NN), as a lead-free antiferroelectric (AFE) material under extensive investigation, exhibits ferroelectric (FE)-like polarization–electric field (P-E) hysteresis loops, characterized by high remnant polarization and large hysteresis. Herein, the local defect structure design is proposed to achieve high energy storage (ES) density in NN-based AFE ceramics. The pinning effect of defect dipoles and the enhancement of local structural disorder stabilize the AFE phase and reduce hysteresis losses. Consequently, an excellent ES performance of large recoverable energy density (Wrec) of 9.70 J/cm3 and high efficiency (η) of 88.75 % is concurrently obtained in NN-based relaxor AFE ceramics, with outstanding charge–discharge performance (PD∼413.2 MW/cm3, WD∼4.47 J/cm3), which are significantly improved compared to other reported values in lead-free ES ceramics. This indicates that NN-based ceramics are candidates for advanced ES capacitors and provides a feasible modulation approach for the development of new lead-free high-performance dielectric materials.

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.

Enhancing comprehensive energy storage properties in Pb-free relaxor AFE/FE system via heterogeneous structure tuning and defect engineering

Multi-phase NaNbO3 (NN) exhibits high adjustability on the ordering of both polarization and oxygen octahedral tilt, becoming a perfect carrier to design heterogeneous structure for boosting comprehensive energy storage properties. To balance the energy storage density and efficiency, the coexistence of the relaxor antiferroelectric (AFE) with high polarization capability and the relaxor ferroelectrics (RFE) with high efficiency is designed in this work by introducing Sr0.7Bi0.2□0.1Ti0.75Ta0.2□0.05O3 (SBTT) into NaNbO3-BiFeO3. As a result, an outstanding capacitive energy density (Wrec) of 12.25 J cm−3 with a high η of 83 % can be achieved in NN-BF-SBTT ceramic, which can be identified as a novel heterogeneous coexisting structure with the crossover of high polarization capability in relaxor AFE and high efficiency in RFE in terms of high-resolution TEM. Furthermore, grain refinement and the dense structure inhibit the leak current, suppress the concentration of oxygen vacancy defects and raise the activation energy (Ea), thus enhancing the EB. These excellent energy storage properties overcome the trade-offs between the two sets of parameters (Wrec-η, ΔP-EB), offering a refreshing strategy for the development of high-performance ceramic capacitors.

Mn-inlaid antiphase boundaries in perovskite structure

Improvements in the polarization of environmentally-friendly perovskite ferroelectrics have proved to be a challenging task in order to replace the toxic Pb-based counterparts. In contrast to common methods by complex chemical composition designs, we have formed Mn-inlaid antiphase boundaries in Mn-doped (K,Na)NbO3 thin films using pulsed laser deposition method. Here, we observed that mono- or bi-atomic layer of Mn has been identified to inlay along the antiphase boundaries to balance the charges originated from the deficiency of alkali ions and to induce the strain in the KNN films. Thus, rectangular saturated polarization-electric field hysteresis loops have been achieved, with a significantly improved twice remanent polarization of 114 μC/cm2 with an applied electric field of 606 kV/cm, which can be comparable to that of the typical Pb-based thin films. Moreover, we directly see the Mn occupation at the A-site of KNN perovskite structure using atomic-scale microstructure and composition analysis. The Mn-inlaid antiphase boundary can further enrich the understanding of perovskite crystal structure and give more possibilities for the design and optimization of perovskite materials.

Enhanced energy storage properties in (Bi0.5Na0.5)0.5Sr0.5TiO3- modified lead-free NaNbO3 antiferroelectric ceramics

The lead-free antiferroelectric material NaNbO3 (NN) is highly regarded for its exceptional breakdown electric field strength (Eb) and substantial recoverable energy storage density (Wrec). However, the significant energy loss of NN reduces its Wrec and η under a strong electric field, constraining its application in energy storage domains. This study explores a novel approach by integrating the relaxation ferroelectric (Bi1/2Na1/2)1/2Sr1/2TiO3 (BNST) into NN to create NN-BNST relaxation anti-ferroelectrics, aiming to enhance their energy storage capabilities. The incorporation of BNST not only effectively reduces the grain size of NN but also disrupts its long-range ordered structure, forming polar nanoregions (PNRs) that mitigate energy density loss. Both Wrec and η of NN ceramic are significantly improved with increasing the concentration of BNST. Optimal results are achieved with the 0.75NN-0.25BNST ceramics, which demonstrate a high energy storage density (Wrec = 3.83 J/cm3) and conversion efficiency (η = 76 %) while achieving an Eb of 236 kV/cm. The analysis of Eb enhancement in NN-BNST ceramics is conducted through considerations of grain size, band-gap width, and activation energy, offering a robust framework for developing new NN-based antiferroelectrics for energy storage applications.

Enhanced polarization fatigue behavior in lead-free ferroelectric (K, Na)NbO3 thin films by Mn doping

Enhanced polarization fatigue behavior in lead-free ferroelectric (K, Na)NbO3 thin films by Mn doping

Large Piezoelectricity Induced by Internal Stress in (K,Na)NbO3 Single Crystals.

Achieving a high piezoelectric response and excellent stability is essential for practical applications of ferroelectric materials. Herein, large piezoelectricity of d33 = 167 pC/N and kt = 0.52 is found in a K0.7Na0.3NbO3 lead-free ferroelectric single crystal without poling, which is comparable to the artificially poled KNN crystals. The large piezoelectricity is maintained up to 196 °C, showing excellent thermal stability. It was demonstrated that the high piezoelectricity is associated with strong self-polarization in the crystals. The strong internal stress formed during crystal growth gives a preferred spontaneous polarization orientation, resulting in a net macro total polarization. In addition, the internal stress also pins domain wall motions and provides a "restoring force" for the domain switching. This work provides a strategy for designing and optimizing the piezoelectric performance of ferroelectric materials.

Utilizing Domain Engineering to Achieve High-Polarization Relaxor Ferroelectrics for Low-Consumption Ceramic Capacitors.

This study focuses on incorporating NaNbO3 (NN) into the Ba0.85Ca0.15Zr0.9Ti0.1O3 (BCZT) lattice to form (1 - x)BCZT-xNN ceramics. Although antiferroelectricity was not observed, an observed domain-movement-diminishment behavior with increasing NN dopant induced the formation of high polarization walls (HPWs) between adjacent C-phases. The 0.90BCZT-0.10NN composition exhibited superior polarization compared to most BCZT-based ferroelectrics, as validated by mathematical derivation. Integration of these findings revealed a Wrec of 3.86 J/cm3 at 360 kV/cm, with a high Wrec/Eb ratio defining energy consumption efficiency in dielectric capacitors. This work introduces a novel approach to fabricating low-consumption dielectric capacitors. Additionally, a significantly high Wrec of 5.36 J/cm3 was achieved with an NN dopant concentration of 0.30.

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 (&lt;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.

Physical Properties of CaTiO3-Modified NaNbO3 Thin Films.

NaNbO3(NN)-based lead-free materials are attracting widespread attention due to their environment-friendly and complex phase transitions, which can satisfy the miniaturization and integration for future electronic components. However, NN materials usually have large remanent polarization and obvious hysteresis, which are not conducive to energy storage. In this work, we investigated the effect of introducing CaTiO3((1-x)NaNbO3-xCaTiO3) on the physical properties of NN. The results indicated that as x increased, the surface topography, oxygen vacancy and dielectric loss of the thin films were significantly improved when optimal value was achieved at x = 0.1. Moreover, the 0.9NN-0.1CT thin film shows reversible polarization domain structures and well-established piezoresponse hysteresis loops. These results indicate that our thin films have potential application in future advanced pulsed power electronics.