NbO3 Ceramics Research Articles

High piezoelectric performance in lead-free (K, Na)NbO3 ceramics under a low driving field

In this work, lead-free (K0.485Na0.485Li0.03)Nb0.8Ta0.2O3 composition was designed to control the orthorhombic-tetragonal phases boundary near the room temperature as confirmed by Rietveld analysis, high-angle annular dark field scanning transmission electron microscopy, and temperature dependent dielectric constant. A comparative study of the direct and indirect synthesis methods was carried out and their functional properties were optimized as a function of sintering temperature (Ts) and dwell time. Here, we achieved a large dynamic piezoelectric constant (d33*) of 510 pm/V under a very low electric field of 15–30 kV/cm. Moreover, an enhanced static piezoelectric constant (d33) of 335 pC/N was obtained with a high Curie temperature (TC) of 315 °C. The large d33 and d33* simultaneously with high TC in a single composition are promising results in lead-free polycrystalline ceramics. The strategic design of this work opens a new door for the possible development of novel functional materials for device applications.

The effect of ZnO and MnO2 as sintering aids in the preparation of potassium sodium niobate ceramics and electrical characterizations

Potassium sodium niobate (KNN) is an environmentally compatible piezoelectric material for substituting harmful lead-based ceramics. KNN-based ceramics have excellent piezoelectric properties with high Curie temperature. But, KNN faces difficulties during the processing like volatilization of alkali elements, chemical inhomogeneity, low densification, etc. The objective of this research is to investigate the impact of certain metal oxides additions like ZnO and MnO2 as sintering aids to solve the problems of the preparation and hence study the structural and electric properties of K0.5N0.5NbO3 (KNN) ceramics. ZnO and MnO2 added potassium sodium niobate, K0.5N0.5NbO3 was prepared by using the ceramic method. The prepared samples were sintered at 1000 °C for 2h conventionally. The structural properties of the ceramics have been analyzed by using X-Ray Diffractometer. The study demonstrates the formation of the orthorhombic-symmetric perovskite phase in all the prepared samples. The microstructural behavior of the ceramics has been characterized by techniques such as scanning electron microscopy (SEM) and compositional properties were studied by energy dispersive x-ray (EDAX). The effects of metal oxide additions on the electronic properties such as dielectric constant, dielectric loss, impedance properties, Nyquist plot, etc., were studied. The results have been analyzed and discussed in the paper.

Unveiling the electrical performance of flash-sintered potassium sodium niobate

Electrical performance of flash-sintered K0.5Na0.5NbO3 ceramics: after annealing, both conventional and flash-sintered KNN ceramics exhibited electrically homogeneous behaviour similar to that of single crystals.

Influence of milling speed of high energy mechanochemical technique on microstructure and electrical properties of K0.5Na0.5NbO3 ceramics

Influence of milling speed of high energy mechanochemical technique on microstructure and electrical properties of K0.5Na0.5NbO3 ceramics

Tuning optical absorption in perovskite (K,Na)NbO3 ferroelectrics.

The ability to tailor the electronic band structure and optical absorption by appropriate cationic substitution in perovskite oxide ferroelectrics is essential for many advanced electronic and optoelectronic applications of these materials. Here, we explored weak (Ba,Ni)-doping for reducing optical bandgaps in (K,Na)NbO3 ferroelectric films and ceramics. The optical absorption in the broad spectral range of (0.7-8.8) eV was investigated in polycrystalline doped, pure, and oxygen deficient films, in doped epitaxial films grown on different substrates, and in doped ceramics. By comparing optical properties of all films and ceramics, it was established that 1-2 at% of cationic substitutions or up to 10 at % of oxygen vacancies have no detectable effect on the direct (∼4.5 eV) and indirect (∼3.9 eV) gaps. Concurrently, substantial sub-gap absorption was revealed and ascribed to structural band tailing in epitaxial films and ceramics. It was suggested that owing to fundamental strain-property couplings in perovskite oxide ferroelectrics, inhomogeneities of lattice strain can lead to increased sub-gap absorption. The uncovered structurally induced sub-gap optical absorption can be relevant for other ferroelectric ceramics and thin films as well as for related perovskite oxides.

Effects of Sb on structure, micro structure and electrical characteristics of Sb-modified (K0.41Na0.59)NbO3 ceramics

Lead-free (Na0.59K0.41)(Nb1-xSbx)O3 ceramic (x = 0 ÷ 0.12) were prepared by the solid phase reaction method. The influence of Sb concentration on the structure, microstructure and electrical properties of the ceramic was studied. Results indicate that the presence of pure perovskite phase was revealed by XRD patterns recorded for the ceramics, which also showed a shift in structure from orthorhombic to mixed rhombohedral and tetragonal with an increase in x value. At x = 0.06, the ceramics express the best microstructure, the particles were tightly packed with an average particle size of 1.76 µm. The (Na0,59K0,41)(Nb0,94Sb0,06)O3 ceramics have the best dielectric and ferroelectric properties: the ceramic density (r) is 4.48 g/cm3 (relative density: 98.7% of the theoretical value); highest dielectric constant at TC (emax) of 12031; dielectric constant at RT (ε) of 945; low dielectric loss (tanδ) of 0.15; and high remanent polarization (Pr) of 11,2 mC/cm2; and the reactance field (Ec) of 8.7 kV/cm, and the phase transition temperatures (TC) of 372 °C, and (TO-T) of 157 °C.

Phase structure and piezoelectric properties in K/Bi co-doped AgNbO3 lead-free ceramics

The ferroelectric (FE) and anti-ferroelectric (AFE) properties of AgNbO3, an AFE material, can be altered by ion doping. K-doping is an effective strategy to enhance the FE properties by inducing an AFE-FE phase transition in the AgNbO3 ceramics, which boosts the FE and piezoelectric properties of (Ag,K)NbO3 ceramics. In this study, the phase structure and piezoelectric properties of the (Ag,K)NbO3 ceramics were further optimized via Bi doping. Doping with a small amount of Bi shifted the orthogonal-tetragonal (O-T) phase boundary to a lower temperature, leading to enhanced piezoelectric properties at room temperature in the (Ag0.9-3xK0.1Bix)NbO3 (x = 0.01–0.04) ceramics. The room-temperature phase structure of the ceramics changed from the FE phase to the AFE phase as x was increased from 0.01 to 0.04. A d33 of 83 pC/N was obtained for the (Ag0.84K0.1Bi0.02)NbO3 ceramics at room temperature, which increased to 140 pC/N at the O-T phase boundary. This study further reveals the controllable phase structure of AgNbO3-based ceramics for their potential applications as piezoelectric ceramics.

Superior comprehensive energy storage performances in Eu-doped AgNbO3 antiferroelectric ceramics

Antiferroelectric (AFE) dielectrics are considered promising materials for pulse power applications due to their high energy density. However, the energy storage performance of AgNbO3 lead-free AFE ceramics suffers from low breakdown strength (Eb) and weak AFE stability at room temperature. Along these lines, in this work, the tape-casting process together with Eu-doping was used to improve Eb and enhance AFE stability of the AgNbO3 ceramics. As a result, an ultrahigh recoverable energy storage density of 10.0 J/cm3 was obtained in the (Ag0.91Eu0.03)NbO3 ceramic, which surpasses all the reported values of AgNbO3-based ceramics in the literatures. Meanwhile, the recoverable energy storage density of (Ag0.91Eu0.03)NbO3 ceramic showed excellent temperature- and frequency-stability. Interestingly, a remarkable discharge energy density of 8.0 J/cm3 was obtained in the pulsed charge/discharge test. These results clearly indicate that the (Ag0.91Eu0.03)NbO3 ceramics prepared via the tape-casting process exhibit great potential for energy storage applications and shed light on the design of energy storage ceramics in other materials.

Dy/Sr‐codoped (K0.5Na0.5)NbO3 multifunctional transparent‐ferroelectric ceramics with adjustable white‐light emission

AbstractTraditional solid‐state luminescent materials (e.g., phosphors and microcrystalline glasses) have attracted extensive attention due to their high energy efficiency and long lifespan. However, their application scope is limited by complex compositions and manufacturing processes, as well as single‐function. In this study, solid‐state reaction was utilized to prepare transparent‐ferroelectric (K0.5Na0.5)NbO3 (KNN) ceramics by simply codoping with Dy3+ and Sr2+, providing possibilities for large‐scale production. Ceramics exhibit high optical transmittance, high‐quality white‐light emission and relaxor ferroelectric feature. Under irradiation of UV light, photochromic behavior occurring in the ceramics, resulting in modulating the optical performances, especially quality of emitted white light. Multifunctionality can expand latent applications of KNN‐based ceramics from white light‐emitting diodes to modulated optoelectronic devices.

High energy storage characteristics for Ba0.9Sr0.1TiO3 (BST) doped Na0.7Bi0.1NbO3 (NBN) ceramics

In recent years, lead-free energy storage ceramics have been widely used as a new type of energy storage material with great application prospects. In this study, a modified NaNbO3 (NN) based ceramic, Na0.7Bi0.1NbO3 (NBN), is used as the matrix, and Ba0.9Sr0.1TiO3 (BST) is added as a doping agent. A series of (1-x)Na0.7Bi0.1NbO3-xBa0.9Sr0.1TiO3 (xBST, x = 0.1, 0.2, 0.3, 0.4) solid solutions have been designed and prepared using the solid-phase sintering method. The breakdown field strength (Eb) of 0.3BST ceramics reached 445 kV/cm, an unexpectedly ultra-high energy storage density (W) of 4.48 J/cm3 and a recoverable energy density (Wrec) of 3.47 J/cm3. In terms of charging and discharging performance, the ceramics have a low charging and discharging time of t0.9 = 1.38 μs. In addition, 0.1BST exhibits a high energy conversion efficiency of η = 87.35 %. These results confirm that (1-x)NBN-xBST ceramics are promising energy storage materials.

Preparation and properties of K0.48Na0.52NbO3 ceramics for bone scaffolds via digital light processing

Lead-free piezoelectric ceramics are expected to be used for artificial bone scaffolds since they can generate electrical signals and promote recovery, but it is still difficult to fabricate piezoelectric scaffolds with complex structures. In this work, digital light processing (DLP) technology was used to fabricate potassium sodium niobate (K0.48Na0.52NbO3, KNN) bone scaffolds with gyroid triply periodic minimal surface. Suspension was first optimized to ensure both high solid loading (42 vol%) and high cure depth (>50 μm). KNN porous scaffolds (porosity: 60%) and other samples for tests were printed successfully. Then, influences of sintering temperature on microstructure, relative density and mechanical properties were discussed. Results showed that when sintered at 1090 °C, printed KNN ceramics had the highest relative density (90.11%) and lowest open porosity (5.75%), and exhibited the most satisfying mechanical properties (compressive strength: 33.85 MPa, elastic modulus: 1.87 GPa, flexural strength: 35.40 MPa, hardness: 2.39 GPa), which can meet the requirements of cancellous bone. Finally, the electric properties of samples at room temperature were verified. With d33 being 113.67 ± 2.49 pC/N and Pr being 19.94 μC/cm2, printed KNN ceramics showed comparable piezoelectric and ferroelectric performances with traditionally dry-pressed samples. These results indicated that DLP technology is competitive in preparing KNN piezoelectric bone scaffolds for implantation.

Effects of CaCO3 additive on the phase, physical, mechanical, and microstructural properties of zirconia-toughened alumina-CeO2-Nb2O5 ceramics

This work studied the effects of CaCO3 additive on the phase, physical, mechanical, and microstructural properties of zirconia-toughened alumina–CeO2–Nb2O5 ceramics prepared via wet milling. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were utilised to analyse the role of secondary phases, particularly hibonite, and their impact on the phase, physical, mechanical, and microstructural properties of this type of ceramic. EDX analysis showed that the hibonite phase contributed to elongated grains among the secondary phases. Vickers indentations indicated a significant difference in the compositional adjustment efficiency among the composites. Excellent Vickers hardness and fracture toughness for 1.0 wt% CaCO3 added resulted in 7.9% hibonite at 1,422.46 HV and 5.84 MPa√m, respectively.

Significant improvement of comprehensive energy storage performance and transparency in Sr0.7La0.2TiO3-doped (K,Na)NbO3 lead-free ceramics

Although transparent ceramics are highly desirable for practical applications, it is challenging to achieve outstanding energy storage properties and high transparency simultaneously in (K, Na)NbO3 ceramics. Herein, through a combination of modifying crystal symmetry and refining domain size and grain size, a high recoverable energy storage density Wrec ≈ 4.04 J cm−3, a high efficiency η ≈ 73 %, and good optical transmittance (≈ 77 % at 2000 nm, ≈ 60 % at 780 nm) are realized. Of particular significance is that an excellent discharge energy density of ≈ 2.43 J cm−3, a superior discharge current density of ≈ 1551 A cm−2, and a high discharge power density of ≈ 233 MW cm−3 are simultaneously achieved in 0.93(K0.5Na0.5)NbO3-0.07 Sr0.7La0.2TiO3 ceramics, outperforming all reported KNN-based transparent ceramics. This work exhibits a paradigm for achieving high performance KNN-based ceramics, and the transparent dielectric ceramics reported here are expect to expand hybrid electronic device applications.

Photoluminescence properties of Ba0.7Sr0.3TiO3:Sm3+ modified K0.5Na0.5NbO3 perovskite oxide ceramics

Ba0.7Sr0.3TiO3:Sm3+ modified KxNa(1-x)NbO3 ceramics with perovskite-type structure were synthesized via solid state sintering method. Sm3+ ions doping was designed for substituting both A and B sites in the ABO3 structure, Sm3+ doped Ba0.7Sr0.3TiO3 (Ba0.7Sr0.3TiO3:Sm3+) oxide precursor powders with the chemical formula of Ba0.7Sr0.3-xSmx(Ti1-xSmx)O3 (x=0.005 ， 0.015 ， 0.025) were synthesized. Combined Ba0.7Sr0.3TiO3:Sm3+ with K0.5Na0.5NbO3, the perovskite-type solid solution composite ceramics were fabricated via solid phase sintering method. X-Ray diffraction was used for investigating the phase structure of the precursor powders and luminescent composite ceramics. The photoluminescence properties of the Sm3+ ions in the Ba0.7Sr0.3TiO3-K0.5Na0.5NbO3 composite ceramic materials were systematically investigated by exploring the effects of composition of the composites, excitation wavelength and temperature on photoluminescence.

Structure and electrical properties of cold-sintered strontium-doped potassium sodium niobate

Cold sintering is an attractive method for sintering ferroelectric ceramics at temperatures at or below 300 °C. While we can practically obtain bulk samples by introducing a transient liquid and applied pressure, the mechanisms of sintering and final functional properties of cold-sintered ceramics are far from being understood. Here, we investigate the influence of grain size and sintering parameters on the microstructure and ferroelectric properties of 0.5 % Sr-doped K0.5Na0.5NbO3 ceramics. By comparing with the conventionally-sintered samples, we find that cold-sintered ceramics have higher dielectric permittivity and lower dielectric losses, which we attribute to smaller grains and higher relative density. Using atomic-scale analysis, we point out the presence of numerous lattice dislocations that likely act as pinning sites and thus inhibit any significant polarization-switching behaviour. Due to the slim P–E loop and high dielectric breakdown fields of the cold-sintered ceramics we consider its potential for energy storage applications.

High‐performance KNN piezoceramics with reproducibility and chemical stability. Part II: Innovative melt‐reaction route

AbstractIn the first part, a means to synthesize high‐density homogeneous (K,Na)NbO3 (KNN) ceramics with high piezoelectric performance and chemical stability at low spark‐plasma sintering temperature was found. However, these properties could not be obtained reproducibly, thus this second part is focused on solving this issue. Here, instead of doing a fine pulverization of raw materials prior to the reaction, the powders are ultimately mixed in the molten state and quenched to keep a single stoichiometry. A fast quenching is found to promote a better homogenization of the KNN phase upon annealing. Additionally, the coarse‐ground KNN powder is pre‐annealed before fine pulverization to preserve its high crystallinity. This innovative procedure prevents the formation of parasitic phases, leading with it to high‐performance undoped KNN ceramics (d33 ≈ 145 – 154 pC/N, kp ≈ 47–48% and kt ≈ 35 – 42%), while achieving both high reproducibility and chemical stability.

Revealing the influence of Nb-doping on the crystal structure and electromechanical properties of (K, Bi)(Mg, Ti, Nb)O3 ceramics

Revealing the influence of Nb-doping on the crystal structure and electromechanical properties of (K, Bi)(Mg, Ti, Nb)O3 ceramics

Oriented and ultrafine-grain potassium sodium niobate piezoelectric ceramics prepared by heterogeneous microcrystalline transformation

The rapid growth of platelet templates with a large volume results in poor density and repeatability for textured Na0.5K0.5NbO3 (KNN) ceramics. To synthesize needle-like templates with small volume, a heterogeneous microcrystalline transformation method was proposed. Acicular heterogeneous microcrystalline were synthesized from the precursor with tungsten bronze structure. The experimental results suggested that the perovskite phase on the surface of these particles could undergo epitaxial growth and complete texture evolution in the matrix. Dense textured KNN ceramics were prepared by templated grain growth method using the obtained heterogeneous microcrystalline as templates. In addition, the KNN nano-powder was synthesized with a high crystallinity when the precursor was completely transformed, which was an ideal raw material for the preparation of ultrafine-grain KNN ceramics. This work provides a new way for the preparation and microstructure control of high-performance lead-free piezoelectric ceramics.

Correlation between crystal structure, bond characteristics, Raman vibrations, and improved microwave dielectric properties of high-performance Zn0.5Zr0.5NbO4 ceramics: First principle calculation and experiment

The structure–performance mechanism provides new insights into performance modification and materials discovery. Herein, the electronic structure, Raman vibration, chemical bond factors and enhanced microwave dielectric properties of Zn0.5Zr0.5NbO4 ceramics through oxygen-assisted reaction sintering were investigated by Raman spectroscopy, first-principle calculations, and complex P–V-L theory. Pure-phase Zn0.5Zr0.5NbO4 ceramics were synthesized under oxygen-assisted reaction sintering, confirmed by XRD refinement and Raman analysis. Systematic vibration analysis was first introduced to provide complete mode assignments and Raman shift. Optimized microstructure with full density was obtained through morphology and EDS analysis. First-principle calculations indicated that the d orbit exerts the main contribution to Fermi energy with energy gap of 3.51 eV and Nb–O bonds may possess strong vibration, exhibiting a remarkable effect on dielectric loss. P–V-L results showed that Nb–O bonds have a significant influence on the dielectric constant and Q×f value while the Zn–O bonds dominate the τf value. In addition, high-performance Zn0.5Zr0.5NbO4 ceramics were fabricated through oxygen-assisted reaction sintering at 1250 °C, with εr = 28.4, Q×f = 79,800 GHz, and τf = −47.7 ppm/°C, exhibiting tremendous superiorities for commercial production.

Deciphering the role of A-site ions of AZrO3-type dopants in (K, Na)NbO3 ceramics

As one of the most important lead-free piezoelectric candidates, potassium sodium niobate [(K, Na)NbO3, KNN] has gained popularity due to its attractive functional properties, which are much improved by chemical modifications. However, there still remains an insufficient understanding of how these dopants influence the structure and performance of KNN ceramics. Herein, we comparatively studied a series of changes triggered by introducing (Bi0.5Na0.5)ZrO3, BaZrO3, and PbZrO3 into the KNN matrix. The analysis highlights their different roles in modulating the orthorhombic-tetragonal phase transition temperature (TO-T) by considering discrepancies in the electronegativity and radius among Bi3+, Ba2+, and Pb2+ ions. The synergistic effects of the large electronegativity and the small radius of the Bi3+ ion are the key to regulating TO-T, which is relatively unaffected by Pb2+ and Ba2+ ions. Based on experimental results and first-principles calculations, a multi-scale model is proposed to summary the general law of how the electronegativity and radius of the A-site ion in AZrO3-type dopants synergistically affect the phase structure, ferroelectric domains, and electrical properties of KNN ceramics. Therefore, this work helps understand the role of chemical dopants in the structure and performance of KNN ceramics and promote the future composition design for high performance.