NaNbO3 Ceramics Research Articles

A novel lead-free NaNbO3–Bi(Zn0.5Ti0.5)O3 ceramics system for energy storage application with excellent stability

Many researches have been referred to the AFE structure of NaNbO3 in order to develop high power energy storage for NaNbO3-based ceramic. However, the square P-E loops with large Pr was observed in NaNbO3 ceramics due to the coexistence of AFE and the field-induced metastable FE, which suppress the energy storage property of NaNbO3-based ceramics. In the present work, lead-free (1-x)NaNbO3-xBi(Zn0.5Ti0.5)O3 (abbreviated as (1-x)NN-xBZT) dielectric ceramics were prepared via the traditional solid-state route. The structures, relaxor behavior and energy storage property of (1-x)NN-xBZT ceramics were investigated with the introduction of BZT. The slim P-E loops were obtained while x = 0.09–0.12 and the maximum discharge energy storage density (Wrec = 2.1 J/cm3) was obtained while x = 0.09, meanwhile a high energy storage efficiency (η = 76%) was achieved. Moreover, the charge-discharge tests show that 0.91NN-0.09BZT ceramics can achieve fast discharge rate (50 ns) and exhibit excellent stabilities of temperature and electric field, which guarantee the application prospect of 0.91NN-0.09BZT ceramics for lead-free plus power system in a wide temperature range.

The influence of electrical field on (K,Na)NbO3-based ceramics over polymorphic phase transition composition region

By investigating the responding behavior of Li modified (K,Na)NbO3 ceramics under external electrical field, a coincidence phenomenon had been observed. It was found that the amplitude of piezoelectricity enhancement for these ceramics with pure orthorhombic, coexistence and tetragonal phase were consistent with the variation amplitude for the transition temperature from orthorhombic to tetragonal (TO-T). The interpretation of the remnant polarization (Pr) had rationally demonstrated the enhancement of piezoelectricity for these three kinds of ceramics. The residual polarization energy induced by remnant polarization (Pr) was about to affect the thermodynamic equilibrium state of these ceramics and accordingly ΔTO-T varied with these poled ceramics.

Enhanced antiferroelectricity and double hysteresis loop observed in lead-free (1−x)NaNbO3-xCaSnO3 ceramics

Well-defined polarization-electric field double hysteresis loops are rarely observed in pure NaNbO3 (NN) ceramics due to the metastability of the field-induced ferroelectric phase. In order to stabilize the antiferroelectric phase, various ABO3-type binary oxides were incorporated into a NaNbO3 ceramic, where the B-site is occupied with transition elements. In this work, CaSnO3 was chosen to construct the NaNbO3-based solid solution by reducing the Goldschmidt tolerance factor and ionic polarizability. X-ray diffraction patterns, transmission electron microscopy images, and Raman spectra indicate enhanced antiferroelectricity. Typical double hysteresis loops were also observed from polarization-electric field measurements in ambient conditions with slightly weakened maximum polarization as the content of CaSnO3 increased. Our results reveal the generality of this strategy and pave the way for various applications involving high-power energy for NaNbO3-based ceramics.

Proposal of a rhombohedral-tetragonal phase composition for maximizing piezoelectricity of (K,Na)NbO3 ceramics

Great progress in the field of piezoelectricity of (K,Na)NbO3 (KNN) lead-free ceramics, driven by emerging rhombohedral-tetragonal (R-T) phase boundary, has instigated research activity regarding elaborate controls of the phase boundary structure. Through phase-microstructure-property mapping in KNN ceramics doped with Bi-containing perovskite oxides, in this study we for the first time report the existence of a certain R-T phase boundary state by which to create maximum piezoelectric response in KNN systems. This phase boundary condition is usually comprised of approximately 15% R phase and 85% T phase, regardless of the choice of dopant material. Any deviation from this phase composition, either by inclusion of orthorhombic (O) phase or by enrichment of R phase, has a negative effect on the value of d33. These findings can provide useful guidance for chemical doping control associated with the type of phase boundary and the phase composition for advanced KNN-based materials.

Evolving antiferroelectric stability and phase transition behavior in NaNbO3-BaZrO3-CaZrO3 lead-free ceramics

The stability of antiferroelectricity in NaNbO3 ceramics was found to evolve with co-doping x mol% CaZrO3 and 6 mol% BaZrO3, from a dominant ferroelectric (FE) orthorhombic Q phase (x = 0) to a gradually stabilized antiferroelectric (AFE) orthorhombic P phase owing to different ionic radii of Ba and Ca ions. Although a complete AFE P phase appears at x = 0.5, the field induced AFE-FE phase transformation is irreversible at first, and then becomes partially reversible at x = 1 and finally completely reversible at x = 3. The above-mentioned change process proves to be associated with the enhancing stability of antiferroelectricity with x, as evidenced by means of dielectric, polarization and strain properties as well as in/ex-situ synchrotron x-ray diffraction and Raman spectra. A composition-field phase diagram for the NN-based lead-free AFE ceramic was constructed on basis of the phase structural change, which would provide a clear understanding of how ion doping influences its antiferroelectricity.

Potentiality of Bi and Mn co-doped lead-free NaNbO3 ceramics as a pyroelectric material for uncooled infrared thermal detectors

The pyroelectric materials have immense applications in the uncooled infrared thermal detectors. However, owing to increasing environmental concerns due to Pb element, it is required to explore novel, high-performance, environmental-friendly pyroelectric materials. This is the first study to report about the pyroelectric properties of lead-free NaNbO3 ceramics, which displayed a high pyroelectric coefficient of 1.85 × 10−8 C cm-2 K−1 and figures of merit as Fi = 0.67 × 10−10 m V−1, Fv = 3.33 × 10−2 m2 C−1, and Fd = 5.32 × 10-5 Pa−1/2 at room temperature. Also, highly temperature-stable pyroelectric characteristics were also observed in NaNbO3 ceramics due to the high depolarization temperature of 280 ℃. The high pyroelectric properties and temperature stability were a result of the electric field induced irreversible phase transition from antiferroelectric to ferroelectric. Hence, we can conclude that lead-free NaNbO3 ceramics are a novel and promising candidate for pyroelectric detectors in a wide temperature range, especially for large area detectors and pyroelectric point detector.

Electrocaloric behavior and piezoelectric effect in relaxor NaNbO3‐based ceramics

AbstractWe firstly reported the electrocaloric properties in relaxor (1−x−y)NaNbO3–yBaTiO3–xCaZrO3 ceramics, and high electrocaloric effect (∆T ~0.451 K and∣∆T/∆E∣~0.282 Km/MV) can be realized in the ceramics (x = 0.04 and y = 0.10) under low temperature and low electric field. Relaxor behavior of NaNbO3 ceramics can be found by doping both BaTiO3 and CaZrO3. In addition, optimized piezoelectric effects (d33 ~235 pC/N and d33* ~230 pm/V) can be observed in the ceramics (x = 0.04 and y = 0.10) due to the involved morphotropic phase boundary (MPB). Excellent piezoelectric effect (ie, d33~330 pm/V at 41°C, and d33*~332 pm/V at 60°C) can be found because of the characteristics of MPB. Good temperature reliability of piezoelectric effect can be shown because of both MPB and relaxor behavior. We believe that the ceramics with high electrocaloric effect and good piezoelectric effect can be considered as one of the most promising lead‐free materials for piezoelectric devices.

Flash sintering of sodium niobate ceramics

Dense and stoichiometric NaNbO3 ceramics were difficult to be prepared by conventional sintering methods because Na2O easily volatilized at elevated temperature. In this work, the volatility of Na2O was suppressed by applying an electrical field assisted sintering method. Flash sintering was preformed successfully on NaNbO3 ceramics under the electrical fields ranging from 400 to 700 V/cm. The Na/Nb ratio of dense ceramic remained similar to that of the green sample. Our work demonstrated that flash sintering was an alternative technique for fabricating dense and high-purity ceramics with highly volatile species.

(K0.5Na0.5)NbO3 lead-free ceramics with improved piezoelectricity and field-induced strain

The sintering additive 0.4ZnO-0.6B2O3 (abbreviated as ZnB) was proposed to improve the sintering behavior of (K,Na)NbO3 ceramics. The influence of ZnB on the microstructure and electrical properties of (K,Na)NbO3 ceramics was carefully investigated in detail. Results demonstrated that during the sintering process a liquid phase can form at a relative low temperature, which could favor and accelerate the densification of (K,Na)NbO3 ceramics. Moreover, it was found that (K,Na)NbO3 ceramics with 1.2 wt% ZnB exhibited excellent properties with the piezoelectric constant of d33 = 134 pC/N and planar electromechanical coupling coefficient of kp = 40%. Moreover, the field induced strain of 0.135@5 kV/mm was also achieved with this composition. Meanwhile, the mechanism for this enhancement of property was discussed.

Stable antiferroelectricity with incompletely reversible phase transition and low volume-strain contribution in BaZrO3 and CaZrO3 substituted NaNbO3 ceramics

In this work a reproducible double polarization versus electric field (P-E) hysteresis loop clearly reveals a room-temperature stable antiferroelectricity (AFE) in virgin NaNbO3 (NN) samples doped with 6 mol% BaZrO3 and 3 mol% CaZrO3. Inconsistent but sprout-like strain versus field (S-E) curves without any negative strains between the first and non-first cycles yet display an incompletely reversible field induced AFE-ferroelectric (FE) phase transition. In/ex-situ synchrotron x-ray diffraction results suggest irrecoverable AFE states with orthorhombic and monoclinic structures before and after electric cycling, respectively, which generate an irreversible strain contribution including both irreversible volume (22%) and lattice (78%) strains. Frequency-dependent measurements of P/S-E curves demonstrate the rest of remanent strains from the time effect of back-switching from field induced FE to AFE equivalently existing in strain loops of any cycles at a fixed frequency. Compared with virgin samples, post-cycled samples exhibit a completely reversible monoclinic AFE-monoclinic FE phase transition but a relatively small poling strain. It is of particular note that the contribution of the volume strain to the poling strain is only 20% in AFE NN-based ceramics, in which a positive longitudinal strain and a negative transverse strain are concurrently observed, challenging a common knowledge that both strains in two directions should be positive for traditional Pb-based AFE ceramics. The experimental results provide new insights into the AFE phase stability of NN and an exciting possibility to take advantage of NN-based antiferroelectric ceramics for large-displacement actuators in future.

XLiNbO3-(1-x)(K,Na)NbO3 ceramics: A new class of phosphors with tunable upconversion luminescence by external electric field and excellent optical temperature sensing property

In this study, Er3+-doped and Er3+/Yb3+-co-doped xLiNbO3-(1-x)(K,Na)NbO3 (xLN-(1-x)KNN) ferroelectric ceramics were synthesized by a solid state reaction process and the samples were found to exhibit tunable upconversion luminescence (UCL) under an external electric field as well as excellent optical temperature-sensing properties. By altering the polarization time, UCL intensity was effectively controlled under an external electric field. Furthermore, an optimal UCL was observed in a 0.4LN-0.6KNN:Er3+,3Yb3+ sample and its excellent optical temperature sensitivity (0.006 K−1 at 643 K) from 83 to 663 K was 131% higher than that of 0.4LN-0.6KNN:Er3+. These results suggested that xLN-(1-x)KNN ferroelectric ceramics were promising candidates for an opto-electronic integrator and optical temperature sensors with high sensitivity and broad temperature range.

Energy storage properties of NaNbO3-CaZrO3 ceramics with coexistence of ferroelectric and antiferroelectric phases

Anti-ferroelectric materials with large saturated polarization, small remnant polarization, and moderate breakdown strength are receiving increasing attention for modern high-power electrical systems. Here we demonstrated that by incorporating CaZrO3 into NaNbO3 ceramics, the antiferroelectricity in NaNbO3-CaZrO3 solid solutions could be stabilized at room temperature. The effects of phase constitution and microstructure on the dielectric properties, electrical breakdown strength, and energy storage properties of the NaNbO3-CaZrO3 ceramics were investigated. Ferroelectric and antiferroelectric phase coexistence in the NaNbO3-CaZrO3 was confirmed by XRD and TEM analyses. With increasing CaZrO3 content, the grain size was reduced, and the dielectric breakdown strength was improved. Therefore, a high energy density of 0.55 J/cm3 and efficiency of 63% was obtained in the NaNbO3-0.04CaZrO3 ceramics. These lead-free NaNbO3-CaZrO3 antiferroelectrics with good electrical energy storage can be exploited for high-power storage devices.

Temperature dependent dielectric relaxation and ac–conductivity of alkali niobate ceramics studied by impedance spectroscopy

Sodium niobate (NaNbO3) ceramics is prepared by conventional solid state reaction method at sintering temperature 1150 °C for 4 h. The structural information of the material has been investigated by X-ray diffraction (XRD) and Field emission scanning electron microscopy (FE-SEM). The XRD analysis of NaNbO3 ceramics shows an orthorhombic structure. The FE-SEM micrograph of NaNbO3 ceramics exhibit grains with grain sizes ranging between 1 µm to 5 µm. The surface coverage and average grain size of NaNbO3 ceramics are found to be 97.6 % and 2.5 µm, respectively. Frequency dependent electrical properties of NaNbO3 is investigated from room temperature to 500 °C in wide frequency range (100 Hz–5 MHz). Dielectric constant, ac–conductivity, impedance, modulus and Nyquist analysis are performed. The observed dielectric constant (1 kHz) at transition temperature (400 °C) are 975. From conductivity analysis, the estimated activation energy of NaNbO3 ceramics is 0.58 eV at 10 kHz. The result of Nyquist plot shows that the electrical behavior of NaNbO3 ceramics is contributed by grain and grain boundary responses. The impedance and modulus spectrum asserts that the negative temperature coefficient of resistance (NTCR) behavior and non-Debye type relaxation in NaNbO3.

Effect of NiO substitution on the structural and dielectric behaviour of NaNbO3

The structural and dielectric properties of NiO substituted NaNbO3 ceramics are reported. The orthorhombic (Pmna) crystal structure of NaNbO3 transforms to a lower symmetry monoclinic phase (Pbma) after the dilute dispersion of NiO. X-ray photoelectron spectroscopy reveals pentavalent “Nb,” monovalent “Na,” and divalent “Ni” states along with the signatures of non-local screening effects. The antiferroelectric to paraelectric transition (TAFE) accompanied by a structural change from the orthorhombic to the tetragonal phase shifts by 55 °C toward the low-temperature side, whereas the morphotropic phase boundary (TO-M) moves toward a higher temperature by 28 °C for nominal substitutions (x≤0.10). The generalized Lyddane-Sachs-Teller expression (ε0−S′ε∞)=(ωlωt)2 and thermodynamic free energy models are employed to explain the anomalous behaviour of the temperature dependence of relative dielectric permittivity (εr(T)) across TAFE and TO-M. The frequency dependence of ac-conductivity σac(ω) follows the Jonscher power law (σac = σ(0) + Aωs), suggesting the dominance of the phonon-assisted hopping mechanism, whereas the frequency independent term (σ(0)) was explained by Funke's Jump-Relaxation Model.

Enhanced dielectric and energy-storage properties in ZnO-doped 0.9(0.94Na0.5Bi0.5TiO3−0.06BaTiO3)−0.1NaNbO3 ceramics

[0.9(0.94Na0.5Bi0.5TiO3−0.06BaTiO3)−0.1NaNbO3]-xZnO (NBT-BT-NN-xZnO, x=0, 0.5wt%, 1.0wt%, 1.5wt%, and 2.0wt%) ferroelectric ceramics were fabricated using a conventional solid-state reaction method. The effects of ZnO content on dielectric, energy-storage and discharge properties were systematically investigated. Dielectric constant and difference between maximum and remanent polarization were significantly improved by ZnO doping. Dielectric constant of NBT-BT-NN-1.0-wt% ZnO was 3218 at 1kHz and room temperature, i.e. one time bigger than that of pure NBT-BT-NN ceramic. As a consequence, a maximum energy-storage density of 1.27J/cm3 with a corresponding efficiency of 67% was obtained in NBT-BT-NN-1.0-wt% ZnO ceramic. Moreover, its pulsed discharge energy density was 1.17J/cm3, and 90% of which could be released in less than 300ns. Therefore, ZnO doped NBT-BT-NN ceramic with a large energy-storage density and short release time could be a potential candidate for applications in high energy-storage capacitors.

Improved piezoelectricity and luminescence of Er3+/Yb3+ co-doped (K, Na)NbO3 ceramics by microwave sintering

ABSTRACTYb2O3 doped (K,Na)NbO3-0.5% Er2O3 (KNNEr) ceramics with the composition around the morphotropic phase boundary was synthesized by microwave sintering. KNN co-doped Yb2O3/Er2O3 ceramics exhibited enhanced ferroelectric, piezoelectric properties owing to the donor doping effect. The optimal performance of d33 = 115 pC/N, kp = 0.37, ϵr = 620 and tanδ = 4.9% were obtained for the ceramics with the addition of 0.25 mol% Yb2O3. And the green and red up-conversion emission intensities of these ceramics excited under 980 nm increased with the increasing content of Yb2O3. The results suggest that the KNNEr-Yb2O3 ceramics have potential application as a multifunctional device by integrating its excellent electrical and luminescence properties.

Study of Electrical Properties and Luminescence of Conventional Furnace and Microwave-Sintered Er3+/Yb3+ Co-doped (K, Na)NbO3 Ceramics

Yb2O3 doped (K0.5Na0.5)NbO3–0.5% Er2O3 (KNNEr) ceramics were synthesized by microwave sintering. (K, Na)NbO3 co-doped Yb2O3/Er2O3 ceramic exhibited enhanced piezoelectric and ferroelectric properties owing to the donor doping effect. The optimal performances of d 33 = 115 pC/N, k p = 0.37, e r = 620 and tanδ = 4.9% were obtained for the ceramics with the addition of 0.25 mol% Yb2O3. The green and red up-conversion emission intensities of KNNEr ceramics excited under 980 nm increased with the increasing content of Yb2O3. The results indicated that the KNNEr-Yb2O3 ceramics have potential application of multifunctional device by combining its excellent luminescence and electrical properties.

Low-temperature sintering and piezoelectric properties of CuO-doped (K,Na)NbO3 ceramics

The lead-free piezoelectric [(K0.485Na0.515)0.935Li0.065](Nb0.99Ta0.01)O3 (KNLNT) ceramics with a high mechanical quality factor (Qm) were prepared at low sintering temperature below 950°C for multilayered piezoelectric devices. Co-doping effect of 1mol% Na2CO3 and 0–1mol% CuO on the densification and piezoelectric properties were investigated. Co-doping effectively decreased the sintering temperature of KNLNT ceramics to 920°C. The co-doped KNLNT ceramics had a bimodal size distribution of large abnormal grains and small matrix grains above 900°C. When the sintering temperature increased above 900°C, a dielectric constant (εr) and loss (tan δ) decreased considerably and concurrently mechanical quality factor (Qm) greatly enhanced. The co-doped KNLNT ceramic with 1mol% Na2CO3 and 0.5mol% CuO had a high Qm and excellent piezoelectric properties when sintered at 940°C: a dielectric constant of 245 and loss (tan δ) of 0.0034, an electromechanical coupling factor (kp) of 0.449, and Qm of 904.

Macroscopic ferroelectricity and piezoelectricity in nanostructured NaNbO3 ceramics

NaNbO3 sits at an instability between its ferroelectric and antiferroelectric phases, but its nanoscale polarization behavior is rarely reported. In this work, we produced high-density NaNbO3 nanostructured ceramics with a grain size of 50 nm by spark plasma sintering of nanocrystalline powder, which was obtained by mechanosynthesis. The nanostructured ceramics exhibited a symmetrical ferroelectric loop and increased relative permittivity. We believe that the increased internal stress at the nanoscale stabilized the ferroelectric domain structure, which promoted macroscopic piezoelectricity, demonstrating its potential uses in nanoelectromechanical systems.

NaNbO3 nanoparticles: Rapid mechanochemical synthesis and high densification behavior

Sodium niobate (NaNbO3) is an important lead-free electronic ceramic, but it is difficult to obtain high sintering densification due to the strong volatility of alkali metal elements. Reducing particle size of the precursor powder is believed to be an effective method to improve sintering activity, further to achieve high densification. In this work, pure perovskite NaNbO3 nanoparticles with mean size of 15 nm have been synthesized by a facile one-step route using the mechanochemical method. The evolution of crystal structure and morphology of the particles milled for different times were investigated, and a transformation mechanism has been proposed to elucidate the formation processes of NaNbO3 nanoparticles. Furthermore, high-density (98%) NaNbO3 ceramics were successfully prepared from nanoparticle compact without any sintering additives. In addition to the Curie temperature of 360 °C, a diffuse dielectric peak ∼100 °C has been observed, evidencing an intrinsic P-Q phase transition. After the polarizing treatment, the obtained NaNbO3 ceramic exhibited a high piezoelectric coefficient, d33 = 37 pC/N.