NaNbO3 Research Articles

NaNbO3 modified BiScO3-BaTiO3 dielectrics for high-temperature energy storage applications

Among the lead-free compositions identified as potential capacitor materials, BiScO3-BaTiO3 (BS-BT) relaxor dielectrics exhibit good energy storage performance. In this research, 0.4BS-0.6BT is considered as the parent composition, with NaNbO3 (NN) addition intended to substitute the A and B site cations. The NN modified BS-BT ceramics exhibit excellent temperature stability in terms of their dielectric properties, with the room-temperature dielectric constant on the order of 500–1 000 and variation less than 10% up to 400 °C. In addition, NN has a high band-gap energy leading to increased breakdown strength and energy storage properties in modified compositions. The highest breakdown strength was achieved for 0.4BS-0.55BT-0.05NN, being on the order of 430 kV/cm, and a high energy density of 4.6 J/cm3 with high energy efficiency of 90% was simultaneously achieved. Of particular importance is that the variation of the energy density was below 5% due to the temperature-insensitive dielectric constant, while ∼90% energy efficiency was retained over the temperature range of 25–160 °C. The improved temperature stability with NN addition makes this composition promising for high temperature capacitor and dielectric energy storage applications.

Sharpening polycrystalline phase boundary for potassium sodium niobate ceramics with MnF2 modification

AbstractThe influence of anion on structure and performance is unclear in potassium sodium niobate ((K,Na)NbO3; KNN)‐based ceramics, while cation doping has been widely researched. Here, the phase structure and electrical properties are explored in MnF2‐doped KNN ceramics. Significantly, sharp rhombohedral–orthorhombic (R–O) and orthorhombic–tetragonal (O–T) phase boundary as well as reduced diffusion degree is exhibited in the ceramics along with little changed phase transition temperatures due to the optimized F− content at O site, which is different from that of cation replacement for A and B sites. Notably, the domain wall motion is facilitated due to the increased A vacancy and decreased O vacancy along with strengthened polarity, originating from the higher valence state and electronegativity of F− with respect to O2−. And then, enhanced ferroelectricity is realized via MnF2 modification, the piezoelectricity is elevated in turn. This work presents a new idea of anion doping for controlling structure and properties in perovskite materials.

Realizing enhanced energy storage and hardness performances in 0.90NaNbO3\u22120.10Bi(Zn0.5Sn0.5)O3 ceramics

Ceramic dielectric capacitors have a broad scope of application in pulsed power supply devices. Relaxor behavior has manifested decent energy storage capabilities in dielectric materials due to its fast polarization response. In addition, an ultrahigh energy storage density can also be achieved in NaNbO3 (NN)-based ceramics by combining antiferroelectric and relaxor characteristics. Most of the existing reports about lead-free dielectric ceramics, nevertheless, still lack the relevant research about domain evolution and relaxor behavior. Therefore, a novel lead-free solid solution, (1−x)NaNbO3−xBi(Zn0.5Sn0.5)O3 (abbreviated as xBZS, x = 0.05, 0.10, 0.15, and 0.20) was designed to analyze the domain evolution and relaxor behavior. Domain evolutions in xBZS ceramics confirmed the contribution of the relaxor behavior to their decent energy storage characteristics caused by the fast polarization rotation according to the low energy barrier of polar nanoregions (PNRs). Consequently, a high energy storage density of 3.14 J/cm3 and energy efficiency of 83.30% are simultaneously available with 0.10BZS ceramics, together with stable energy storage properties over a large temperature range (20–100 °C) and a wide frequency range (1–200 Hz). Additionally, for practical applications, the 0.10BZS ceramics display a high discharge energy storage density (Wdis ≈ 1.05 J/cm3), fast discharge rate (t0.9 ≈ 60.60 ns), and high hardness (H ≈ 5.49 GPa). This study offers significant insights on the mechanisms of high performance lead-free ceramic energy storage materials.

Multiscale Structure Engineering for High-Performance Pb-Free Piezoceramics

ConspectusThe increasing world energy crisis drives humans to harvest the energy in nature as much as possible without heavily damaging the environment. However, most of the energy in nature cannot be used directly. Therefore, pursuing technologies or matter that can directly interconvert different energies has been one of the most cutting-edge fields in science and technology. Such a magic ability exists in true-life piezoelectric materials that generate charge when being given a force and vice versa, rendering them highly promising for energy harvesting and conversion because of the tremendous mechanical energy on the earth, such as tide energy. Thus, piezoelectric materials, represented by the lead zirconate titanate (Pb(Zr, Ti)O3, PZT) family, have been largely used in various traditional and burgeoning fields, such as electronic information, biomedical treatment, and wearable flexible electronic devices, and are one of the most important favorites in multidisciplinary fields. However, Pb is highly toxic. Driven by environmental protection and concern for human health, Pb-free piezoceramics are rapidly being developed to hopefully replace Pb-based ones. In particular, the renewal of Restriction of the use of certain Hazardous Substances (e.g., RoHS 2), issued by the European Union, declared that replacement of PZT “...may be scientifically and technologically practical to a certain degree...”. Therefore, developing high-performance Pb-free piezoceramics has become more urgent than ever. In this context, some Pb-free piezoceramics, represented by potassium sodium niobate ((K, Na)NbO3, KNN), barium titanate (BaTiO3, BT), bismuth barium titanate ((Bi, Na)TiO3, BNT), and bismuth ferrite (BiFeO3, BFO), stand out because of their unique or similar traits. However, several key challenges, including an inferior overall performance compared to Pb-based counterparts and an unclear structure–property relationship from multiscale viewpoints, have severely hindered the development of Pb-free piezoceramics for a long time.Pb-based piezoceramics possess decent performance due to the strategy of phase boundary engineering, which inspired the researchers to pursue it in Pb-free counterparts. In the last 10 years, our group has been aiming at the new phase boundary (NPB) and new physical phenomenon in Pb-free piezoceramics. This Account presents our recent contributions to the development of Pb-free piezoceramics concerning the good performance and emerging phenomenon. First, we introduce the construction of the NPB in KNN-based piezoceramics by emphasizing the role of some key elements (i.e., Bi, Sb, Zr, and Hf). Then, we summarize the effects of the NPB on KNN- and BT-based ceramics and the new physical phenomenon in BNT-based ceramics. The NPB boosts the piezoelectric properties and temperature stability of KNN- and BT-based piezoceramics, comparable to some Pb-based piezoceramics. Combining the NPB and the multilayer ceramics substantially enhances the temperature stability of the piezoelectric constant. A new physical phenomenon of the nanoscale bubble domains with polar topologies is for the first time revealed in BNT-based ceramics, showing potential applications for nonconventional and high-density nonvolatile memories. In particular, we emphasize structure engineering from multiscale viewpoints including the local, microscopic, mesoscopic, and macroscopic structure (e.g., lattice structure, ferroelectric domains, and phase structure). Finally, we provide perspectives on the future developments of Pb-free piezoceramics toward practical applications.

Superior energy storage properties in NaNbO3-based ceramics via synergistically optimizing domain and band structures

A synergistic optimization strategy with regard to ferroelectric domain and band structure is applied to NaNbO3 (NN)-based ceramics. High Wrec and η of 7.33 J cm−3 and 83.68% are achieved simultaneously.

Ultrahigh electric breakdown strength, excellent dielectric energy storage density, and improved electrocaloric effect in Pb-free (1-x)Ba(Zr0.15Ti0.85)O3-xNaNbO3 ceramics

In this study, NaNbO3 (NN) was introduced into Ba(Zr0.15Ti0.85)O3 (BZT) to form a solid solution with relaxor ferroelectric characteristics. The dielectric breakdown strength (BDS) of the specimen with 6 mol.% NN reached 680 kV/cm, the corresponding recoverable energy storage density (Wrec) was 5.15 J/cm3, and the energy storage efficiency (η) was 77%. The dissolution of Na + ions at the A position and Nb5+ ions at the B position of the perovskite structure reduced the concentration of oxygen vacancies in the lattice and compensated for defects. The doped ceramics exhibited lower dielectric loss and better thermal stability: the Wrec value was 2 ± 1% J/cm3 at 30–120 °C. In particular, in the 0.02NN ceramics, a ΔT of 1.81 K was achieved at 130 kV/cm, and the operating temperature zone expanded with the increase in doping concentration. The introduction of NN resulted in BZT ceramics that possess excellent energy storage performance and electrocaloric effect properties.

Understanding the origin of the high piezoelectric performance of KNN-based ceramics from the perspective of lattice distortion

Although both phase structure and fraction can affect the electrical properties of (K, Na)NbO3 based ceramics, few studies have examined the effects of lattice distortion on their electrical properties. In this work, we prepared (1-x)K0.48Na0.52NbO3-x(NaSbO3-(Bi0.45Sm0.05)Li0.5ZrO3) lead free piezoelectric ceramics with a multiphase coexistence region by regulating the doping component. The c/a ratio of the tetragonal phase greatly influenced the electric properties of the ceramics. The c/a ratio of the tetragonal phase decreases from 1.0102 to 1.0080 and subsequently increases to 1.0090. When the c/a of the tetragonal phase reaches its minimum value, the ceramic with x = 0.04 has the best piezoelectricity (d33∼348 pC/N). Our research exhibits an alternative way to further understand the mechanism of electric property improvement of (K, Na)NbO3 based ceramics with multiphase coexistence.

Achieving stable relaxor antiferroelectric P phase in NaNbO3-based lead-free ceramics for energy-storage applications

Compared with antiferroelectric (AFE) orthorhombic R phases, AFE orthorhombic P phases in NaNbO3 (NN) ceramics have been rarely investigated, particularly in the field of energy-storage capacitors. The main bottleneck is closely related to the contradiction between difficultly-achieved stable relaxor AFE P phase and easily induced P-R phase transition during modifying chemical compositions. Herein, we report a novel lead-free AFE ceramic of (1-x)NN-x(Bi0.5K0.5)ZrO3 ((1-x)NN-xBKZ) with a pure AFE P phase structure, which exhibits excellent energy-storage characteristics, such as an ultrahigh recoverable energy density (Wrec) ∼4.4 J/cm3 at x = 0.11, a large powder density PD ∼104 MW/cm3 and a fast discharge rate t0.9–45 ns. The analysis of polarization-field response, Raman spectrum and transmission electron microscopy demonstrates that the giant amplification of Wrec by ≥ 177 % should be mainly ascribed to the simultaneously and effectively enhanced AFE P-phase stability and its relaxor characteristics, resulting in a diffused reversible electric field-induced AFE P-ferroelectric phase transition with concurrently increased driving electric fields. Different from most (1-x)NN-xABO3 systems, it was found that the reduced polarizability of B-site cations dominates the enhanced AFE P-phase stability in (1-x)NN-xBKZ ceramics, but the almost unchanged tolerance factor tends to cause the AFE R phase to be induced at a relatively high x value.

Synthesis of (K, Na)NbO3 piezoelectric crystals with tunable K/Na ratios

(K, Na)NbO3 (KNN) lead-free piezoelectric crystals with different K/Na molar ratios were synthesized through a hydrothermal method using isopropanol/deionized water as the reaction medium. It is shown that cube-like KNN crystals were synthesized at a relatively low [OH–] concentration. The structure of the as-synthesized KNN crystals transfers from a NaNbO3-type orthorhombic phase to a KNbO3-type tetragonal phase with the increase of the K/Na ratio. This principle is also instructive in a finer range of K/Na ratio (0.71:0.29–0.73:0.27), indicating a facile synthesis route and recommended conditions for the synthesis of KNN materials with a morphotropic phase boundary (MPB) between NaNbO3 and KNbO3.

Rapid thermal annealing induced engineering of surface and photoluminescence properties of (K,Na)NbO3 thin films for optoelectronic applications

The present study is focused on understanding the mechanism of luminescence behavior and how it gets affected with post annealing temperature via rapid thermal annealing of (K,Na)NbO3 thin films. The crystalline KNN perovskite structure with preferred (001)-orientation is observed upon annealing at 750 and 800 °C. After annealing, the evolution kinetics of surface features is resulted from the simultaneous evaporation-recondensation and volume diffusion of particles. The volatilization of alkali species after annealing and, in contrast, the lattice oxygen and Nb5+ chemical state of niobium related to KNN is enhanced. Narrowing of optical band gap after annealing is attributed to the generation of shallow defects deep below the conduction band owing to order–disorder and/or distortion in NbO6 octahedra. Photoluminescence (PL) quenching behavior is observed after RTA with 290 nm excitation wavelength. A strong blue emission is observed at 800 °C after exciting with 266 nm wavelength. The kinetics of decay lifetime from time-resolved PL results revealed the enhancement of transitions more likely via radiative states. The RTA induced results specify that KNN can be one of the promising candidates for use in LEDs, smart glass windows, optical switches/sensors, and optoelectronic devices.

Structural and piezoelectric properties of textured NLKNS‐CZ thick films and their application in planar piezoactuator

Abstract0.97(Na0.5‐xLixK0.5)(Nb0.89Sb0.11)O3‐0.03CaZrO3 [(N0.5‐xLxK)(NS)‐CZ] piezoceramic (x = 0.325) has a pseudocubic‐tetragonal‐orthorhombic (PC‐T‐O) multi‐structure. The PC structure formed in this piezoceramic was identified as the R3m rhombohedral structure. This piezoceramic showed the large piezoelectric charge constant (d33) of 515 pC/N due to the PC‐T‐O multi‐structure. The NaNbO3 (NN) templates were used to texture the (N0.5‐xLxK)(NS)‐CZ thick films along the (001) direction, and the textured thick film (x = 0.0375) had a large Lotgering factor of 95.6%. The PC‐T‐O multi‐structure was observed in this thick film (x = 0.0375), but the thick film (x = 0.0325) showed a PC‐O structure owing to the diffusion of the NN templates into the thick film. The textured thick film (x = 0.0375) exhibited an increased d33 of 625 pC/N because of the PC‐T‐O multi‐structure and the lineup of grains along the [001] direction. A textured thick film (x = 0.0375) was used to fabricate a planar‐type actuator to confirm its applicability to electrical devices. This actuator exhibits large acceleration (580.3 G) and displacement (150 μm) at a low electric field of 0.2 kV/mm with a short response time of 3.0 ms. Therefore, the (N0.5‐xLxK)(NS)‐CZ thick films are excellent lead‐free piezoceramics.

Giant Grain Growth in (K,Na)NbO3 Ceramics

In this manuscript, an interesting phenomenon is reported. It has been reported that the growth of single crystals is observed in donor-doped (K,Na)NbO3 (KNN)-based ceramics. It is very interesting that the growth happens without the addition of a seed. The growth of huge grains (single crystal, approximately 30 mm,) occurs due to the abnormal grain growth (AGG) in KNN-based ceramics. In the AGG compositions, moreover, the seed plates can be synthesized by not topochemical reaction but simple molten salt synthesis (SMSS) which is a simple-and-cheap process. They can be a good candidate for the seeds at reactive templated grain growth (RTGG) or templated grain growth (TGG) process.

One simple approach, two remarkable enhancements: Manipulating defect dipoles and local stress of (K, Na)NbO3-based ceramics

Although the composition-driven multi-phase coexistence strategy has been widely used to modify the piezoelectric properties of potassium sodium niobate ((K, Na)NbO3, KNN) based ceramics, the trade-off between long-range ferroelectric ordering and chemical additives-induced disorder hinders the further improvement of piezoelectricity and makes the electric field-induced strain temperature-dependent. Herein, to resolve two issues, we proposed a new concept, that is, manipulating defect dipoles and local stress of a pre-constructed multi-phase coexistence through controlling zirconium (Zr) content. We validated the new concept by designing 0.96(K0.4Na0.6)Nb0.955Sb0.045O3-0.04(Bi0.5Na0.5)Zr(1+x)O3 ceramics. In samples with Zr deficiency (i.e., x=-0.1), we obtained high retention of 91% in normalized unipolar strain (Suni) over the temperature range of 30-160 °C, even under low electric fields of 10-20 kV/cm, superior to those of other representative KNN-based ceramics. In samples with slight Zr excess (i.e., x=0.07), we achieved an increase in direct piezoelectric coefficient (d33) and converse piezoelectric coefficient (d33*) by 12% and 25%, respectively, in comparison with that at x=0. The enhanced temperature stability stems from the released domain walls that are pinned by defect dipoles, and the increased d33 (and d33*) originates from the synergetic contributions of the multi-phase coexistence, increased grain size, and stabilization of the ZrO2 secondary phase. Therefore, our new concept would benefit the composition design and performance improvement of KNN-based ceramics in the future.

NaNbO3-CaTiO3 lead-free relaxor antiferroelectric ceramics featuring giant energy density, high energy efficiency and power density

NaNbO3 (NN)-based lead-free antiferroelectric (AFE) ceramics with ultrahigh energy-storage density (Wrec) have attracted increasing attention for applications in high power electronic devices. However, large polarization hysteresis induced by the AFE-ferroelectric (FE) phase transition tends to cause high energy dissipation. In this work, a relaxor AFE orthorhombic R-phase ceramic in (1-x)NN-xCaTiO3 ((1-x)NN-xCT) solid solutions was found to show outstanding comprehensive energy-storage properties with giant Wrec = 6.6 J/cm3, high energy efficiency η = 80% and ultrahigh power density PD = 350 MW/cm3 as × ≥ 0.14. The results of Raman spectrum, Raman mapping and transmission electron microscopy demonstrate that introducing CT in NN will moderately enhance the local-structure inhomogeneity as compared with many other complex perovskites, thus benefiting the gradual transformation from AFE microdomains to AFE nanodomains with increasing CT content. This allows the polarization saturation to be reached at a relatively high electric field. Of particular importance is that the high band-gap in NN and CT, refined grain size and suppressed dielectric loss enable obviously enhanced dielectric breakdown strength. As a result, the proper balance between those different factors leads to an obvious improvement in the overall energy-storage performance of the AFE R-phase region. The above results demonstrate that the local structure engineering is expected to play a crucial role in the achievement of excellent energy-storage properties in NN-based lead-free relaxor AFE ceramics.

Thermal stability of self-polarization in a (K,Na)NbO3 film prepared by the hydrothermal method

Herein, the systematic change in the self-polarization behavior against the post-heat treatment after film deposition was investigated to understand the origin of self-polarization in hydrothermally prepared (K x Na1−x )NbO3 films with x = 0.88 at 240 °C below the Curie temperature. The transverse piezoelectric constant, e 31,f , was evaluated by the cantilever method. The as-prepared films and heat-treated films at 300 °C had an almost perfectly self-polarized state and showed e 31,f of ∼−5.0 C m−2 without applying an electric field as a poling treatment. Also, the piezoelectric response shows good linearity with the asymmetric piezoelectric butterfly curves, showing imprint characteristics. The self-polarized states were maintained until the heat treatment above the Curie temperature. Moreover, the self-polarized film was successfully deposited on the post-heat-treated film without the self-polarized state. This result suggests that the self-polarized state is generated regardless of the polarized state of the underlying layer by the hydrothermal synthesis in which deposition temperature is below the Curie temperature.

Ultrafast synthesis and densification of ZrO2 doped KNN ceramics by reactive flash sintering

AbstractFabrication of dense KNN‐based lead‐free piezoelectric ceramics at low temperatures in short time through a cost‐effective way remains a challenge. Herein, this challenge could be addressed by using reactive flash sintering. It is demonstrated that the phase transformation of KNbO3‐NaNbO3 into (K,Na)NbO3 and densification occur simultaneously during the flash event. Most importantly, ZrO2 doping can greatly decrease the onset flash temperature, which is ascribed to the increased conductivity of sample. In addition, the current limit has a significant effect on the phase transformation and densification. The flash‐sintered KNN ceramics exhibit the good ferroelectric and piezoelectric properties. Furthermore, the ZrO2 doped and undoped KNN ceramics show a comparable coercive field Ec, which may be related to the residual point defects after the flash. Besides the Joule heating, the avalanche generation of point defects is suggested to be responsible for the ultrafast solid‐state reaction and densification rates.

Ultra-fast charge-discharge and high energy storage density realized in NaNbO3–La(Mn0.5Ni0.5)O3 ceramics

Lead-free antiferroelectric (AFE) NaNbO3 (NN) is one of promising materials for dielectric capacitors, but the recoverable energy-storage density and efficiency get restrained owing to huge remanent polarization and limited dielectric breakdown field strength. In this work, a variety of NN based lead-free bulk (1-x)NaNbO3-xLa(Mn0.5Ni0.5)O3 (abbreviated as (1-x)NN-xLMN, x = 0, 0.05, 0.10, 0.15, 0.20) ceramics were designed using a solid-state synthesis method. Remarkably, an ultra-fast charge-discharge speed 47 ns and an acceptable recoverable energy-storage density Wrec ~1.77 J/cm3 with a high efficiency η = 77% were obtained under the Eb of 200 kV/cm at x = 0.05. The superior energy storage performance is attributed to the regulation of domain size and voltage resistance by special ions substitution of A and B sites. This work not only proposes an efficient strategy to realize high recoverable energy-storage density and efficiency, but also provide an candidate material for application of advanced pulsed power capacitors.

Insight for the construction of R-T phase boundary in KNN piezoceramics from the view of energy band structure and electron density

The crystal structures and associated energy band structures of classic lead-based PZT (PbZr0.5Ti0.5O3) and lead-free KNN (K0.5Na0.5NbO3) piezoelectric ceramics prepared by a solid-state method are systematically studied based on the First-principles calculations. For better understanding relations between energy band structures and the phase structures in the PbZr0.5Ti0.5O3 and KNN, the components PT (PbTiO3)/PZ (PbZrO3) and KN (KNbO3)/NN (NaNbO3) are also calculated. The results suggest that the vital contribution to R-T morphotropic phase boundary (MPB) in PbZr0.5Ti0.5O3 comes from the hybridization of A-site and B-site ions, which causes stretching and tilting of oxygen octahedron and therefore leads to the formation of R and T phases. The KNN behaves differently. Moreover, it's concluded that the band structure highly inherited from tetragonal PbTiO3 plays an important role in the construction of the R-T phase boundary according to the comparison of PbZr0.5Ti0.5O3 and KNN. In general, the work inspires an idea from the view of energy band structure to realize R-T phase coexistence as well as improved piezoelectric properties in KNN-based lead-free piezoceramics.

Role of oxygen vacancy defects in piezoelectric thermal stability characteristics of Mn-doped (K,Na,Li)NbO3 piezoceramics

Piezoelectric thermal stability characteristics of (K,Na,Li)NbO3 ceramics were investigated with a particular focus on the role of oxygen vacancy defects, by excluding the lattice distortion or microstructural effects with the help of a low level of Mn doping (less than 1.0 mol%). Benefiting from the reduction of intrinsic oxygen vacancy defects, controlled Mn doping (0.25 mol%) could achieve excellent ferroelectric/piezoelectric activity and superior thermal aging resistance. Beyond this doping level, however, the defect dipoles combined with extrinsic oxygen vacancies, although advantageous to the hardening effect, deteriorated the piezoelectric thermal stability and aging resistance including room-temperature properties. The thermal dissociation and migration of oxygen-vacancy-associated defect dipoles were considered mainly responsible for negating the ability to restore the initial poled domain state with defect-dipole-induced polarization. Results demonstrated the importance of keeping the intrinsic and extrinsic oxygen vacancy levels as low as possible for lead-free (K,Na)NbO3 systems with more thermally stable domain structure.

Realizing High Comprehensive Energy Storage and Ultrahigh Hardness in Lead-Free Ceramics.

Due to the presence of pores and low density, a high recoverable energy density (Wrec) value is usually obtained at the cost of energy storage efficiency (η) in lead-free potassium sodium niobate [(K, Na)NbO3, KNN] based ceramics, which also affects the hardness of ceramics, finally limiting the further development of practical applications. A high Wrec (∼3.60 J/cm3 ) and a high η (∼74.2%) are obtained in 0.975K0.5Na0.5NbO3-0.025LaBiO3 (0.975KNN-0.025LB) ceramics simultaneously under a high dielectric breakdown strength (DBS) of 340 kV/cm, together with a fast discharge rate (t0.9 ∼ 46 ns) and high power density (PD ∼ 49.4 MW/cm3). Further analysis of the intrinsic electronic structure is carried out via the first-principles calculation based on the density functional theory (DFT). An ultrahigh hardness (H) of 6.63 GPa can be accordingly obtained. This work combines excellent energy storage properties and ultrahigh hardness, which provides significant guidelines for applications in pulsed-power systems.