NbO3 Ceramics Research Articles

The achieving enhanced piezoelectric performance of KNN-based ceramics: Decisive role of multi-phase coexistence induced by lattice distortion

Multi-phase coexistence induced by phase boundary regulation is an efficient approach to promote the performance of (K, Na)NbO3 ceramics. Here, [(1-x) (K0.5Na0.5)(Nb0.965Sb0.035)O3 - x (Bi0.5Na0.5)HfO3, x = 0, 0.01, 0.02, 0.03, 0.04, 0.05] [(1-x) KNNS - x BNH] lead-free piezoceramics are prepared through solid-state sintering method. The changes of internal phase structure are analysed by systematic measurements, from which the coexistence of rhombohedral-tetragonal (R-T) multi-phase is confirmed at x = 0.04. The lattice distortion caused by BNH doping induces the coexistence of R-T multi-phase, consequently achieving the best comprehensive properties at x = 0.04 (d33 = 353 pC/N, TC = 285 ℃, εr = 6517, Pr = 15.3208 μC/cm2), which is due to the reduced domain wall energy and more easily deflected domains in the R-T multi-phase coexistence zone. This work is helpful to understand the essence of the multi-phase coexistence caused by doping to improve the piezoelectric performance.

(K0.5Na0.5)NbO3-based photochromic transparent ceramics for high-security dynamic anti-counterfeiting and optical storage applications

Inorganic photochromic (PC) materials are increasingly considered as important media for optical information storage and multi-level encryption anti-counterfeiting. However, most traditional materials are based on their static properties, posing a serious security threat to the stored information. To address this issue, a strategy is proposed for kinetics-tunable PC (K0.5Na0.5)NbO3 ceramic that comprehensively utilize the static and dynamic characteristics of matters. The prepared (K0.5Na0.5)0.95Sr0.04Pr0.01NbO3 (SP-y) ceramics displayed two different excellent optical properties and distinct applications (smart windows and dynamic information storage) simply by adjusting sintering temperature (y). The sample SP-1180 exhibited high transparency (∼62% at 780 nm) while SP-1150 possessed ultrafast response time (3 s) and extremely high coloration contrast (ΔRI = 91%). More importantly, the kinetics of photoreaction could be modulated by varying illumination wavelength and time. Furthermore, a new anti-counterfeiting or optical storage method was designed by constructing SP-1150 with different PC properties. The encoded or stored information was recorded using two commercial lasers (370 & 405 nm or 370 & 520 nm), suggesting that the security level of this anti-counterfeiting design could be significantly improved. This work will drive more innovative designs in smart windows, high-security dynamic anti-counterfeiting and optical storage applications in the future.

Low-temperature synthesis of K0.5Na0.5NbO3 ceramics in a wide temperature window via cold-sintering assisted sintering method and enhanced electrical properties

High temperatures (≥ 1100 °C) and narrow temperature window (∼ 20 °C) for sintering dense K0.5Na0.5NbO3 ceramics always deteriorate their electrical properties. Here, via cold-sintering assisted sintering method, dense K0.5Na0.5NbO3 ceramics were obtained in a wide temperature span between 800 °C and 1000 °C. An aqueous solution of NaOH and KOH mixture was used as transient liquid. Effects of liquid content (LC), molar concentration (MC) of liquid, cold-sintering temperature (TCS), and post-annealing temperature (TAN) on densification and electrical properties of the ceramics were investigated in detail. The ceramics prepared using LC = 10 wt%, MC = 10 mol/L, TCS = 350 °C, and TAN = 900 °C exhibit excellent electrical properties with d33 = 123 pC/N, εr = 609, tanδ = 0.021, Pr = 28.0 μC/cm2, Pm = 39.2 μC/cm2, and Ec = 20.3 kV/cm. Compared to the ceramics with same or similar compositions via conventional solid-state sintering, the present K0.5Na0.5NbO3 ceramics exhibit excellent electrical properties. The study endows the cold-sintering assisted sintering the successful method to prepare K0.5Na0.5NbO3 ceramics at low temperatures and in a wide temperature window.

Introduction of Sr(In0.5Ta0.5)O3 to Modulate Phase Structure and Optoelectronic Properties of (K0.5Na0.5)NbO3 Ceramics

Introduction of Sr(In0.5Ta0.5)O3 to Modulate Phase Structure and Optoelectronic Properties of (K0.5Na0.5)NbO3 Ceramics

Effect of sintering additives on the densification and dielectric properties of Sr0.5Ba0.5Nb2O6 ceramics synthesized by a soft-chemistry method

Nano-crystalline Sr0.5Ba0.5Nb2O6 powders with addition of LiNbO3 or LiF as sintering additives were prepared by a soft-chemistry synthesis using polyethylene glycol. Calcination at 600 ​°C results in nanocrystalline powders (dcryst. ​≈ ​30 ​nm) which were sintered between 1000 and 1300 ​°C to ceramic bodies. By addition of 10 and 20 ​mol% LiNbO3, the sintering temperature was reduced by about 200 ​K and the activation energy of the initial stage of sintering decreases from 386 to 271 ​kJ ​mol−1. The sintering aid improves the grain growth and dense ceramic bodies were obtained after sintering at 1125 ​°C for 1 ​h. A higher LiNbO3 content favors the formation of a pillar-like microstructure. XRD patterns of ceramics sintered above 1000 ​°C show only reflections of the Sr0.5Ba0.5Nb2O6 phase indicating an incorporation of LiNbO3 in the Sr0.5Ba0.5Nb2O6 structure. Dielectric measurements reveal a diffuse phase transition and a relaxor-like behavior. The phase transition temperature (Tm) depends on the sintering conditions and is between 117 and 127 ​°C for 10 ​mol% LiNbO3, which is very close to pure Sr0.5Ba0.5Nb2O6, while addition of 20 ​mol% shifts Tm to around 200 ​°C and the transition becomes slightly more diffuse. The optical band gap of the samples is ​≈ ​3.3 ​eV and depends slightly on the sintering conditions. We also tried LiF as sintering aid, but this leads to the formation of considerable amounts of secondary phases in the ceramics and relative densities of only 82%.

Dielectric relaxation and high recoverable energy density in (1-x)(0.3BiFeO3-0.7SrTiO3)-xK0.5Na0.5NbO3 ceramics

(1-x)(0.3BiFeO3-0.7SrTiO3)-xK0.5Na0.5NbO3 (BFO-STO-xKNN, x=0–0.05) ceramics were synthesized by solid state sintering for energy storage application. The grain size of BFO-STO-xKNN increased with KNN content until x=0.01 and then decreased as x increased further. In contrast, the lattice parameter of BFO-STO-xKNN decreased initially with KNN addition and then increased as x increased further. The initial decrease in lattice parameter was explained by the reduced chemical expansion associated with oxygen vacancies, while the latter increase was due to larger ionic sizes of the dopants. The dielectric response in samples without KNN addition resulted from the Maxwell-Wagner effect with the occurrence of a low frequency (500 Hz) peak at room temperature, while the dielectric relaxation in KNN added samples appeared to have the Debye type with the relaxation peak occurring at a high frequency beyond 106 Hz. The BFO-STO samples free of KNN showed a finite DC conductivity due to electronic hopping between Fe2+/Fe3+, which was absent in KNN added samples, and hence they showed extremely low DC conductivity. KNN-added BFO-STO exhibited slim hysteresis loops ideal for energy storage application. A high recoverable energy density (Wrec) of 3.20 J/cm3 with 88.0% efficiency (η) was achieved with the x=0.01 samples at the applied field of 273 kV/cm. The x=0.01 samples also showed good thermal stability of Wrec and η, which varied only 4.0% and 0.8%, respectively, over the temperature range between 25 and 100 °C.

Pulse-poling and characterization of (Na,K)NbO3 ceramics

Conventional direct current (DC)-poling and three different types of pulse-poling were performed on MnO-added Na0.55K0.45NbO3 (NKN) ceramics. While NKN with DC-poling at 4.0 kV mm−1 for a poling time (t p) of 100 s showed a piezoelectric charge coefficient d 33 of 141.3 pC N−1, an almost equivalent d 33 (141.3 pC N−1) was recorded by pulse-poling in only 10 s under a unipolar electric field of 4.0 kV mm−1, with either triangular, or rectangular waveform. Especially when applying a triangular waveform, d 33 was enhanced remarkably with increasing the number of pulse cycles. In contrast, NKN ceramics poled by alternating current (AC) electric field showed a d 33 of less than 135 pC N−1 under any condition. Polarization–electric (P–E) field responses, and domain structure observations via scanning electron microscopy, showed the different poling behaviors for the various poling techniques. These results suggested that the pulse-poling method under unipolar electric field is an efficient poling procedure for NKN ceramics.

Antiferroelectric-like double hysteresis loops in Ag-doped K0.5 Na0.5NbO3 ceramics

In this work, we report the effect of Ag+ doping on the microstructure, dielectric, ferroelectric, piezoelectric, and energy storage properties of the K0.5Na0.5NbO3 (KNN) ceramics for which (K0.5Na0.5)(1-x)AgxNbO3 (KNN-xAg) ceramics with x = 0, 0.01, 0.02 and 0.03 were prepared by the conventional solid-state method. The substitution of Ag+ changes the microstructure of KNN from inhomogeneous bimodal grain distribution to homogeneous densely packed grains with an average grain size of 0.5–2.25 μm. The phase transition (TC) of KNN shifts towards the lower temperature side with Ag+ doping. Antiferroelectric-type double PE loops were observed in Ag-doped KNN ceramics at room temperature, which has improved the energy storage and piezoelectric properties of KNN. For ceramics poled at 2 kV/mm for 30 min, a d33 value of ∼149 pC/N and kp ∼0.41 were obtained. These enhanced properties in Ag-doped KNN are due to the occurrence of double polarization hysteresis loops.

Structural study of the La-modified AgNbO3 lead-free ceramic system

The structural properties in Ag1−x La x NbO3 ceramics (where x = 0.005) have been systematically investigated at room temperature by using X-ray diffraction (XRD) technique and Raman spectroscopy. The studied sample has been synthesized via the conventional solid-state reaction method. The XRD result confirmed the formation of a single-phase with orthorhombic crystal structure for the studied composition. The signature of the Raman spectrum revealed structural modification with the inclusion of the doping element, with respect to the pure AgNbO3 system, showing additional modes in the middle wavenumbers range (570–758 cm−1).

Multifunctionality of rare earth doped 0.925Na0.5Bi0.5TiO3-0.075K0.5Na0.5NbO3 ferroelectric ceramics

Undoped and RE3+ (RE: Pr; Nd; Dy; Ho; Tm) doped 0.925Na0.5Bi0.5TiO3-0.075K0.5Na0.5NbO3 (NBTKN0.075/NBTKN0.075-RE) ceramics were synthesized using the solid-state synthesis method. X-ray diffraction analysis revealed a pure perovskite structure without secondary phases. The Ho, Dy and Tm ions revealed a dielectric curve with a more diffused phase transition associated with a high value of the dielectric constant, while the lowest diffusivities were found for the Nd and Pr ions doped NBTKN0.075. The ferroelectric hysteresis loops show the significant increase of polarization and electric breakdown strengths (BDS) in all doped samples, accompanied by P–E shape changes under the influence of the different RE3+ ions. In the optical studies, the conversion of near- infrared light to visible light was investigated for Ho3+ and Dy3+ doped NBTKN0.075. The sample with Ho3+ produced a strong green-yellow up-conversion (UC) emission. At an excitation of λex = 800 nm, the blue-green UC emission of the Dy ion showed that the UC is due to the energy transfer interaction. CIE diagram with the corresponding (x, y) coordinates were used to clearly identify the overall color of the multichromatic spectral emissions in each spectrum. The additional functionality of up-conversion emission in the ferroelectric NBTKN0.075-RE material, and its positive effects on the electrical proprieties, open the possibility to realize multifunctionality in a wide range of applications.

Phase structure regulation and enhanced Curie temperature of (K,Na)NbO3-based piezoelectric ceramics

ABSTRACT (K,Na)NbO3 (KNN) ceramics can achieve high piezoelectric properties under the action of polymorphic phase boundary (PPB), but their application is always limited by low Curie temperature (T c). In this work, a new system of lead‐free (1-x)K0.4Na0.6Nb0.96Sb0.04O3-xLi0.5Bi0.45La0.05ZrO3 (KNNS-xLBLZ) ceramics is first designed and prepared to search for good piezoelectric properties and high Curie temperature. The crystal structure, dielectric, piezoelectric, microstructure and conductivity of the system were systematically investigated. The analysis of the dielectric temperature dependence reveals that doping Li0.5Bi0.45La0.05ZrO3 increases rhombohedral-orthorhombic phase temperature (T R-O) and decreases orthorhombic-tetragonal phase transition temperature (T O-T), and then achieves O-T phase coexistence at room temperature. In particular, a piezoelectric coefficient (d 33) of 320 pC/N and T c = 290°C are achieved at 0.02. Ceramics prepared by this ion doping and phase regulation method possess high d 33 and T c. These results show that KNNS-xLBLZ ceramics have great potential for application in high-temperature environments.

A Duplex Grain Structure of Dense (K, Na)NbO3 Ceramics Constructed by Using Microcrystalline as Seed

A Duplex Grain Structure of Dense (K, Na)NbO3 Ceramics Constructed by Using Microcrystalline as Seed

Elastic moduli of potassium sodium niobate ceramics: Impact of spark plasma texturing

An alternative sintering methodology, Spark Plasma Texturing (SPT), allowed us to prepare 98.0% dense lead-free piezoelectric (K1-xNax)NbO3 (KNN) ceramics with a homogenous microstructure of small grains. In this work, Resonant Ultrasound Spectroscopy (RUS) was used to measure bulk, K, and shear, G, moduli of SPT KNN for comparison with conventionally sintered (CS) KNN. SPT fabrication resulted in the highest elastic moduli K = 120.3 GPa (127.7 GPa for 100% density) and G = 45.47 GPa (47.2 GPa for 100% density) ever reported for KNN ceramics. Moreover, by collecting RUS data in situ as a function of temperature, phase transitions at temperatures of 464 and 688 K for CS KNN, and 443 and 643 K for SPT KNN ceramics were determined. Low acoustic loss in the stability field of the cubic phase indicated that the ceramics were mechanically robust, while high loss in the stability fields of the tetragonal and orthorhombic structures demonstrated high mobility of ferroelastic domain walls.

SBN-50 ceramics phase transformations in the temperature range 300–700 K according to Raman spectroscopy data

Lattice dynamics of Sr0.5Ba0.5Nb2O6 ceramics is studied by Raman spectroscopy in the temperature range of 300 – 700 K. The temperature of the macroscopic phase transition (∼390 K) was determined from the dependence of the optical modes frequencies. An anomaly was found in the temperature dependence of the mode frequency and half-width (∼565 K), corresponding to the vibrations of the NbO6 octahedron. Possible reasons for the observed feature are discussed.

High strain in Bi0.5Na0.5TiO3-based relaxors by adding two modifiers featuring with morphotropic phase boundary

The electric field-induced strain in lead-free piezoceramics is generally limited to less than 0.4%, which hinders their practical applications such as actuator. Herein we report a new composition of 0.94Bi0.5Na0.5TiO3-0.06Ba0.85Ca0.15Ti0.9Zr0.1O3-xLi0.06(K0.5Na0.5)0.94NbO3 (BNT-BCZT-xLKNN) ceramics by adding two modifiers (i.e., Li0.06(K0.5Na0.5)0.94NbO3 and Ba0.85Ca0.15Ti0.9Zr0.1O3) featuring with a morphotropic phase boundary (MPB) into the Bi0.5Na0.5TiO3 system. The BNT-BCZT-0.02LKNN shows a high strain of 0.5% as well as a strain-electric field ratio (Smax/Emax) of 625 pm/V, which is one of the best performances compared with reported lead-free piezoceramics. Rietveld refinement and microstructure analysis confirmed the existence of tetragonal (P4bm) and rhombohedral (R3c) phases, and a small part of ferroelectric domains embedded into relaxors according to the PFM, both facilitating the relaxor-to-ferroelectric transformation under an external electric field. As a result, a high strain is obtained in the BNT-BCZT-LKNN system. Our work provides an effective strategy for designing novel lead-free materials with high strain.

Dielectric properties of BaTiO3-based ceramics are tuned by defect dipoles and oxygen vacancies under a reducing atmosphere

BaTiO3-2 mol% MnYbO3-2 mol% CaZrO3-x mol Nb2O5 (x = 0, 0.3%, 0.5%, 0.7%) ceramics were successfully prepared via the conventional solid‐state method, followed by sintering in a reducing atmosphere. The effect of Nb2O5 doping on the crystal structure, micromorphology and dielectric properties of sintered samples was studied, and the correlation mechanisms between the microstructure and dielectric properties were further determined. For x = 0.5 mol%, optimal dielectric properties with high permittivity (ԑr ∼ 3570), low dielectric loss (tanδ ∼ 0.013) and large insulation resistivity (ρv ∼ 4.95 × 1011 Ω cm) are obtained. On this basis, the temperature coefficient of the capacitance (ΔC/C25°C) ranges between ±15% over the temperature range from −55 °C to 125 °C, satisfying the EIA X7R standard. Analysis shows that the increased permittivity of the doped ceramics at room temperature is due to enhanced short-range hoping polarization triggered by the formation of defect dipoles ([MnTi″−2NbTi·]× and [YbTi′−NbTi·]×) and the release of oxygen vacancies. The high insulation resistivity is related to the grain size and electron migration in the ceramics. In addition, the improvement in the temperature stability of the ceramics is ascribed to a decrease in the Curie temperature. The polarization mechanism presented in this work can be extended to BaTiO3 materials, and the results have important application value for BME-MLCC devices.

SnO2 doping effects on the phase constitution and microwave dielectric properties of a Co0.5Ti0.5NbO4 system

The effects of Sn4+ substitution on the structure–property relationship of Co0.5(Ti1−xSnx)0.5NbO4 ceramics were studied systemically using the dielectric theory of complex crystals, and the intrinsic dielectric properties were examined. A rutile Co0.5(Ti1−xSnx)0.5NbO4 solid solution was formed, and the properties were examined via X-ray diffraction and transmission electron microscopy. According to Rietveld refinement analysis, Sn4+ increased the axis length and unit-cell volume. The dielectric theory of complex crystals showed that the introduction of Sn4+ leads to a consistent variation between the average bond covalency value and dielectric constant, indicating a decline in dielectric polarizability. However, an evaluation of the lattice energy of chemical bonds revealed a decrease in the structural stability, with a concomitant increase in the dielectric loss. Moreover, far-infrared reflectivity analysis, complex dielectric function analysis, and Terahertz time-domain spectroscopy of the intrinsic dielectric properties of Co0.5(Ti1−xSnx)0.5NbO4 (x = 0.2) ceramic revealed similar results between the theoretical fitting and experimental test.

Correlation between crystal structure and enhanced microwave dielectric characteristics of wolframite-structure Mg0.5Zr0.5NbO4 ceramics

An effective and simple synthesis of high-performance materials exerts a significant influence on low-cost commercial production with high production efficiency. In the present work, the effects of intrinsic factors on the microwave dielectric properties of reaction-sintering Mg0.5Zr0.5NbO4 ceramics were quantified through crystal chemistry, Raman analysis, and bond characteristics. Pure-phase and low-loss Mg0.5Zr0.5NbO4 ceramics were synthesized with an effective and simple reaction-sintering procedure. Detailed Raman vibrations with complete mode assignments were firstly investigated to characterize the lattice vibration. Rietveld refinement and Raman analysis confirmed the formation of pure-phase MgZrNb2O8 ceramics even with the reaction-sintering process. Moreover, well-distributed microstructure with enhanced densification (nearly full density) was verified through SEM and element mapping. Through the chemical bond theory, the dielectric constant was dominated by the Nb–O bond ionicity (fiNb-O). The Q × f was strongly related to the lattice energy (UNb–O) and bond energy (ENb-O) of the Nb–O bond, while the τf value was influenced by the coefficient of thermal expansion of the Mg–O bond (αMg-O), providing guidance for performance modification of Mg0.5Zr0.5NbO4 systems. Excellent microwave dielectric properties for the samples sintered at 1350 °C: εr = 28.6, Q × f = 82,000 GHz (7.1 GHz) and τf = −47 ppm/°C were obtained via the reaction sintering process, exhibiting enormous potential for industrial production.

Composition dependent crossover from ferroelectric to relaxor-ferroelectric in NBT-ST-KNN ceramics

Composition driven crossover from ferroelectric (FE) to relaxor-ferroelectric (RFE) is systematically investigated in (0.8-x)(Na0.5Bi0.5)TiO3-0.2SrTiO3-x(K0.5Na0.5)NbO3 (NBT-ST-xKNN) ceramics in the light of ferroelectric and dielectric (ε) response. The appearance of constricted polarization-electric field loop and double current density-electric field peaks in the proximity of x = 0.02 suggests a co-existence of FE and RFE phases. The system attains a maximumε ∼4200 and tan δ < 0.1 at x = 0.02. Broad ε(T) peaks reveal a greater degree of disorder due to KNN substitution and their deconvolution demonstrates three different relaxation/polarization processes related to low and high-temperature nanodomains. The composition with x = 0.1 exhibits maximum broadness in ε(T) profiles resulting in a temperature-insensitive permittivity variation of ±15% (ε125 °C,100kHz∼2007) over a span of ∼280 °C. A remarkably low (TCε)100kHz of −75 ppm/°C is also achieved for x = 0.1 from 100 to 300 °C proposing it to be a potential capacitor material.

Effect of excessive amount of (Na, K) ion ratio on structural, optical and electrical properties of K0.5Na0.5NbO3 ceramics prepared by solid-state route

Effect of excessive amount of (Na, K) ion ratio on structural, optical and electrical properties of K0.5Na0.5NbO3 ceramics prepared by solid-state route