Fabrication of lead-free piezoelectric (Na(0.5)K(0.5))NbO(3) ceramics by a modified solid-state reaction method

Sodium potassium niobate, (Na(0.5)K(0.5))NbO(3), fine powder has been successfully synthesized at the low temperature of 550 degrees C through a modified solid-state reaction method, in which urea [CO(NH(2))(2)] plays an important role. High-density (Na(0.5)K(0.5))NbO(3) ceramics could be obtained by conventional sintering of the synthesized (Na(0.5)K(0.5))NbO(3) fine powder with the addition of 0.03 mol% Co(3)O(4) as a sintering additive. The crystal structure, microstructure, and dielectric and piezoelectric properties were characterized. The (Na(0.5)K(0.5))NbO(3) ceramic showed a comparatively saturated P-E hysteresis loop. The (Na(0.5)K(0.5))NbO(3) ceramic also displayed piezoelectricity with a piezoelectric constant d(33) of 126 pC/N and a planar electromechanical coupling factor k(p) of 33%.     

Phase and morphology evolution of magnesium niobate powders synthesized by solid-state reaction

Magnesium niobate (MgNb₂O₆; MN) powders have been prepared and characterized by TG-DTA, XRD, SEM and EDX techniques. The effect of calcination temperature, dwell time and heating/cooling rates on phase formation, morphology and chemical composition of the powders are examined. The calcination temperature and dwell time have been found to have a pronounced effect on the phase formation of the calcined magnesium niobate powders. It has been found that the minor phases of unreacted MgO and Nb₂O₅ phases tend to form together with the columbite-type MgNb₂O₆ phase, depending on calcination conditions. It is seen that optimisation of calcination conditions can lead to a single-phase MgNb₂O₆ in an orthorhombic phase. Higher calcination times and heating/cooling rates clearly favoured particle growth and the formation of large and hard agglomerates.     

Synthesis of BaZrO3 by a solid-state reaction technique using nitrate precursors

High phase purity barium metazirconate powders have been synthesized from a modified solid-state reaction. Reactive powders consisting of submicron particles and narrow particle size distribution were obtained by heating a 1:1 molar mixture of barium nitrate and zirconyl nitrate at 800°C up to 8 h. Simultaneous thermal analysis (TG-DTA) assisted in elucidating the probable reaction pathways leading to the formation of the target compound in the BaO-ZrO₂ system. Systematic structural and microstructural characterization on the green powders and the compacts sintered up to 1700°C were carried out. A two-stage sintering schedule consisting of a 6 h soak at 1600°C followed by slow heating up to 1700°C with no dwell, led to highly dense microstructural features.     

Synthesis and processing of nanosized sodium potassium niobate powders

Abstract

Sodium potassium niobate powders have been produced successfully using a Pechini sol–gel method modified with a novel niobium precursor. The decomposition of the gels produced by this method was observed with thermogravimetric analysis and evolved gas mass spectrometry. This showed three main weight loss stages up to 1000°C arising from the loss of water, methane and carbon dioxide. The effect of different heat treatments of the equimolar gel was studied and correlated to particle properties and phase development. The resultant calcined powders were nanosized and single phase with some residual organic material and water. The effect of varying the composition between sodium niobate and potassium niobate was also studied and correlated to particle size and phase development.     

Synthesis and photoluminescence properties of Cl-doped ZnS nanoparticles prepared by a solid-state reaction

ZnS:Cl⁻ nanoparticles with strong blue emission have been synthesized successfully by a solid-state reaction at low temperature. The dependence of photoluminescence (PL) properties of ZnS:Cl⁻ nanoparticles on the Cl⁻ contents was researched, and the influences of the annealing ambience and using polyvinyl alcohol (PVA) during the synthesis on the PL of ZnS:Cl⁻ (Cl/Zn = 0.35) nanoparticles were discussed. X-ray power diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and ultraviolet-visible spectroscopy were used to characterize their structure, chemical state, diameter, surface states, and PL properties. The results showed that ZnS:Cl⁻ nanoparticles had a cubic blende crystal structure and an average crystallite size of 17.40–19.16 nm. The most intensity blue emission peaking at about 425 nm was obtained when Cl/Zn = 0.35 under 330 nm excitation at room temperature. The emission intensity of ZnS:Cl⁻ (Cl/Zn = 0.35) was increased 3-fold than that of ZnS. The results showed that the PL of ZnS:Cl⁻ (Cl/Zn = 0.35) nanoparticles was enhanced after annealing or using PVA during the synthesis, and annealing in vacuum had a stronger effect in improving the luminescence properties of ZnS nanoparticles than in air. This work suggests that it is an effective method to improve the PL intensity of ZnS nanocrystals by doping with Cl⁻ in ZnS.     

Electrical properties of manganese modified sodium potassium lithium niobate lead-free piezoelectric ceramics

Effects of MnO₂ doping on the microstructure, densification, dielectric, ferroelectric and piezoelectric properties of (Na_0.5K_0.5)_0.935Li_0.065NbO₃ (NKLN) lead-free piezoelectric ceramics were investigated. On the one hand, the addition of a small amount of MnO₂ has little effect on the crystalline structure, however, slightly promotes sintering and grain growth, and improves the uniformity of microstructure to a certain degree. On the other hand, MnO₂ doped NKLN ceramics show hard properties in piezoelectric activities, possessing decreased room-temperature dielectric constant, loss tangent and piezoelectric constants d ₃₃, and increased mechanical quality factors Q _m. The 1.2 mol% MnO₂ doped NKLN ceramics have a loss tangent of approximately 1%, a Q _m of ∼170 and a d ₃₃ of 150 pC/N. These effects were considered to come from the formation of oxygen vacancies and the multi-valence states of Mn ions.     

室温固相反应合成碱式碳酸锌

以七水硫酸锌(ZnSO4.7H2O)和碳酸氢铵(NH4HCO3)为原料,以聚乙二醇-400(PEG-400)为模板,通过室温固相反应制备了碳酸锌(ZnCO3)和碱式碳酸锌(ZnCO3.3Zn(OH)2.H2O,basic zinc carbon-ate,BZC)。通过XRD测试及其半定量成分分析,研究了PEG-400剂量和NH4HCO3与ZnSO4.7H2O摩尔比x值对合成产物物相的影响。总结了PEG-400模板辅助合成ZnCO3和BZC的反应机制。结果表明,PEG-400包覆ZnSO4.7H2O颗粒形成模板,模板层的厚度影响固相反应的微观机制———薄层单向扩散与厚层互扩散,局部微环境的酸碱性决定着产物物相,酸性抑制ZnCO3水解,碱性促进ZnCO3水解生成BZC。由据此设计的较高x值(x=3.0)、较低PEG-400剂量(70μL)的合成工艺,制备了单相BZC粉体。     

Synthesis of nanosized nickel hydroxide by solid-state reaction at room temperature

The nanosized cathode material Ni(OH)₂ powder for alkaline batteries was synthesized by solid-state reaction at room temperature through NiC₂O₄·2H₂O as precursor, which was also prepared with solid-state reaction from nickel acetate and oxalic acid at ambient temperature. The precursor and the Ni(OH)₂ samples were characterized by X-ray diffraction (XRD), infrared spectrometry (IR), transmission electron microscopy (TEM) and electrochemical testing. The results revealed that the as-synthesized Ni(OH)₂ sample by this method is β(II)-type phase, and its shape is fibroid with the average particle size of 6–9 nm. Compared with microsized spherical β-Ni(OH)₂, the nanosized β-Ni(OH)₂ exhibits excellent electrochemical performance, such as lower polarization and better charge–discharge properties.     

Effect of calcination conditions on phase formation and particle size of nickel niobate powders synthesized by solid-state reaction

The solid-state mixed oxide method via a rapid vibro-milling technique is explored in the preparation of single-phase nickel niobate (NiNb₂O₆) powders. The formation of the NiNb₂O₆ phase in the calcined powders has been investigated as a function of calcination conditions by TG-DTA and XRD techniques. Morphology, particle size and chemical composition have been determined via a combination of SEM and EDX techniques. It has been found that the minor phases of unreacted NiO and Nb₂O₅ precursors and the Ni₄Nb₂O₉ phase tend to form together with the columbite NiNb₂O₆ phase, depending on calcination conditions. More importantly, it is seen that optimization of calcination conditions can lead to a single-phase NiNb₂O₆ in an orthorhombic phase.     

Orientation dependence of electromechanical coupling factors in KNbO(3)

This paper is concerned with the electromechanical coupling factors for bulk waves in KNbO(3) crystal. The dependence of coupling factors on the orientation of vibrators for various types of vibration modes has been calculated. As a result, it has been found that most of these coupling factors are very large at certain orientations of vibrators. Especially, the maximum coupling factor of the thickness-extensional mode excited with a perpendicular field, k(t ), is as high as 69% for the rotated X-cut by an angle 49.5 degrees about the Y-axis; that of the thickness-shear mode, k(s), is 88% for the X-cut. To the best of our knowledge, these coupling factors are the highest among those of known piezoelectrics. It has also been found that the coupling factor of the width-extensional mode of a thin finite-width plate with electrodes on its edges, k(ww)', is 82% for the rotated Z-cut by an angle 43.5 degrees about the Y-axis. This vibrator would be promising as elements of phased array ultrasonic probes.     

Effects of calcination conditions on phase formation and particle size of indium niobate nanopowders synthesized by the solid-state reaction

A wolframite-type phase of indium niobate, InNbO₄, has been synthesized by a solid-state reaction via a rapid vibro-milling technique. The formation of the InNbO₄ phase in the calcined powders has been investigated as a function of calcination conditions by TG–DTA and XRD techniques. Morphology, particle size and chemical composition have been determined via a combination of SEM and EDX techniques. It has been found that single-phase InNbO₄ powders have been obtained successfully at the calcination condition of 950 °C for 2 h with heating/cooling rates of 30 °C/min. Higher temperatures and longer dwell times clearly favoured particle growth and the formation of large and hard agglomerates.     

纳米LiCo_xMn_(2-x)O_4粉体的制备与电化学性能

采用溶胶一凝胶法并结合热处理工艺制备LiCoxMn2-xO4粉体,结合热处理工艺制备Li-LiCoxMn2-xO4粉体.利用热重一差热分析、X射线衍射、透射电镜、充放电测试等方法对前驱体的热分解行为、粉体的结构、形貌及电化学性质进行了表征,同时研究了钴掺杂量对其结构和电化学性能的影响.结果表明,直接以聚丙烯酸(PAA)为螯合剂合成了稳定的溶胶和凝胶,进一步获得了粒径分布均匀、无团聚的尖晶石LiCoxMn2-xO4纳米粉体.随着钴掺杂量的增加,晶格常数、晶粒尺寸逐渐减小,晶格畸变逐渐增大,但对尖晶石结构影响较小;LiCoxMn2-xO4粉体的放电比容量随着x值增大略有降低,但循环性能得到明显的改善.在电流密度0.1mA/cm2、截止电压3.5～4.3V时,粒径约80hm的LiCo0.1Mn1.9O4粉体首次放电比容量达135mAh/g,20次循环后的稳定放电比容量为118mAh/g,且每次容量衰减低于0.2%,具有较好的电化学性能.     

Influence of calcination conditions on phase formation and particle size of indium niobate powders synthesized by the solid-state reaction

A wolframite-type phase of indium niobate, InNbO₄, has been synthesized by a solid-state reaction via a rapid vibro-milling technique. The formation of the InNbO₄ phase in the calcined powders has been investigated as a function of calcination conditions by TG-DTA and XRD techniques. Morphology, particle size and chemical composition have been determined via a combination of SEM and EDX techniques. Single-phase InNbO₄ powders have been obtained successfully for calcination condition of 900 °C for 4 h or 950 °C for 2 h with heating/cooling rates of 30 °C/min. Higher temperatures and longer dwell times clearly favoured particle growth and the formation of large and hard agglomerates.     

Frequency Agile Infrared Lidar Based on a NonTracking KNbO(3) Optical Parametric Oscillator

We present what is to our knowledge the first mid-IR lidar system based on a KNbO(3) optical parametric oscillator pumped by a Ti:sapphire laser. The optical parametric oscillator works in a nontracking configuration and provides high-frequency agility from 1 to 4 mum. This system constitutes an extension to the IR of UV lidars described previously [Europhys. J. D 4, 231 (1998); Appl. Opt. 37, 2231 (1998); Atmos. Environ. 32, 2957 (1998)] for the determination of aerosol concentrations in urban atmospheres. As first field tests, measurements at 3.5 mum were performed in fog conditions. Water droplet size and concentration were determined from Mie calculations. Quantitative temporal mappings and angular profiles are presented.     

Lead-free KNbO(3) ferroelectric nanorod based flexible nanogenerators and capacitors

In spite of high piezoelectricity, only a few one-dimensional ferroelectric nano-materials with perovskite structure have been used for piezoelectric nanogenerator applications. In this paper, we report high output electrical signals, i.e.?an open-circuit voltage of 3.2?V and a closed-circuit current of 67.5?nA (current density 9.3?nA?cm(-2)) at 0.38% strain and 15.2%?s(-1) strain rate, using randomly aligned lead-free KNbO(3) ferroelectric nanorods (～1?μm length) with piezoelectric coefficient (d(33)?～?55?pm?V (-1)). A flexible piezoelectric nanogenerator is mainly composed of KNbO(3)-poly(dimethylsiloxane) (PDMS) composite sandwiched by Au/Cr-coated polymer substrates. We deposit a thin poly(methyl methacrylate) (PMMA) layer between the KNbO(3)-PDMS composite and the Au/Cr electrode to completely prevent dielectric breakdown during electrical poling and to significantly reduce leakage current during excessive straining. The flexible KNbO(3)-PDMS composite device shows a nearly frequency-independent dielectric constant (～3.2) and low dielectric loss (<0.006) for the frequency range of 10(2)-10(5)?Hz. These results imply that short and randomly aligned ferroelectric nanorods can be used for a flexible high output nanogenerator as well as high-k capacitor applications by performing electrical poling and further optimizing the device structure.     

Compact reflection-grating-based phase conjugator in KNbO(3):Fe crystals

We present the design and the results of experimental investigations of a self-pumped phase conjugator through a reflection grating in a special-cut photorefractive KNbO(3):Fe crystal. High reflectivity, good phase-conjugate fidelity, and fast response time are obtained.     

Synthesis and characterization of SrFe12O19 nanoparticles produced by a low-temperature solid-state reaction method

Ultra-fine nanoparticles of strontium hexaferrite, SrFe₁₂O₁₉, have been synthesized by low-temperature solid-state reaction method without ball-milling process. The effects of the preparing conditions of samples such as calcination temperature, Fe³⁺/Sr² and Na¹⁺/Sr²⁺ mole ratio on the phase composition, particle size and shape and magnetic properties of the calcined samples have been investigated by differential thermal analysis, X-ray diffraction, field emission scanning electronic microscopy, and vibrating sample magnetometery. The X-ray diffraction patterns showed the formation of SrFe₁₂O₁₉ single phase at temperatures as low as 750° C. Fine particles with particle size around 30–100 nm obtained at 750° C with Fe³⁺/Sr² mole ratio of 10. The magnetic measurements and structural analysis showed that particles were single domain and exhibited better magnetic properties than those obtained by the ceramic method.     

Enhancement of Q(m) by co-doping of Li and Cu to potassium sodium niobate lead-free ceramics.

Lead-free piezoelectric ceramics KNN modified by Li-substitution and CuO addition have been synthesized, and the piezoelectric and dielectric properties were measured. A morphotropic phase boundary (MPB) between orthorhombic and tetragonal phases was formed with Li-substitution. The co doping of Li and Cu markedly enhanced the mechanical quality factor (Q(m)) in comparison with the sole doping of Li and Cu. Anomalous anti ferroelectric-like hysteresis curves were observed in 2 mol% CuO-doped ceramics. The anti-ferroelectric-like curves were changed to that of normal ferroelectrics following poling. A model based on the formation of the internal bias field (Ei) due to the movements of space charges was proposed to explain these phenomena. It was considered that the Ei stabilized the spontaneous polarization (Ps) and suppressed the domain wall motion to enhance the Q(m). The highest Qm obtained in this study was 742. The [(Na0(0.5)K0(0.5))(0.96)Li0(0.04) ] NbO(3) + 0.45 mol% CuO ceramics showed a high Q(m) value of 414 with a high piezoelectric constant d(33) of 100 pC/N.     

Synthesis and characterization of Al-Zn/Al2O3 nano-powder composites

Composites consisting of Al-Zn/Al2O3 have been synthesized using high energy mechanical milling. High energy ball milling increases the sintering rate of the composite powder due to increased diffusion rate. Owing to the finer microstructure, the hardness of the sintered composite produced by using the mechanically milled nanocomposite powder is significantly higher than that of the sintered composite produced by using the as-mixed powder. The mean crystallite size of the matrix has been determined to be 27 nm by Scherrer equation using X-ray diffraction data. The powders have been characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and differential thermal analysis (DTA). The effect of high-energy ball milling and subsequent annealing on a mixture of Al and ZnO has also been investigated. DTA result show that the reaction temperature of Al-ZnO decreases with the increase in the ball milling time.