Reaction between the tetragonal tungsten bronze niobate K2Sr4Nb10O30 and the perovskite Pb(Mg1/3Nb2/3)O3

The search for dielectric materials with a high dielectric constant and ′_r = ƒ(T) curves with a flat profile fitting the X7R specification is still ongoing. Promising results were obtained by mixing compounds with closely related structures, such as the tetragonal tungsten bronze (TTB) niobate K₂Sr₄Nb₁₀O₃₀ and the perovskite Pb(Mg_1/3Nb_2/3)O₃ (PMN). The present study, based on three methods of synthesis, explores the origin of the spreading out of the dielectric curves ′_r = ƒ(T). For the composition 10x K_0.2Sr_0.4NbO₃ (KSN) + (1 − x)Pb(Mg_1/3Nb_2/3)O₃ (PMN) with x = 0.3–0.6, the three synthesis methods provided similar characteristics and for the highest perovskite ratio (x = 0.3), the ′_r = ƒ(T) curve exhibits a flat profile. When lithium is used as a sintering agent, ′_r = ƒ(T) curves present a linear dependency with the temperature. These materials are also characterized by a structural and a microstructural inhomogeneity. Two phases TTB and perovskite type, different from KSN and PMN, are present after calcination and sintering, but not evenly distributed. The PbO loss during sintering also contributes to the evolution of the properties of the material.     

热障涂层陶瓷层材料LnMgAl11O19(Ln=La,Nd)粉体的性能

用共沉淀法制备LaMgAl₁₁O₁₉粉体,证明了提高沉淀温度和pH值可使前驱粉体的性能明显提高。应用差热分析和X射线法研究了磁铅石相的生成温度和粉体的结晶度;使用Scherrer 公式并结合XRD谱计算了晶粒尺寸;用扫描电镜观察了各工艺参数的前驱粉体在1500℃时效5 h后的形貌;使用Malvern ZEN3600粒度仪和Manual measurement软件分析了粉体硬团聚的尺寸分布;用Nd₂O₃, Gd₂O₃, Sm₂O₃替代La₂O₃,研究了制备多种镁基六铝酸盐粉体的可行性。结果表明：在pH值为11.5、沉淀温度为60℃条件下制备的前驱粉体,其完全相变为纯LaMgAl₁₁O₁₉粉体的初始温度为1440℃,比在常温下沉淀的前驱粉体降低了150℃,磁铅石相的生成效率明显提高。在1500℃时效5 h的粉体其晶粒为纳米尺度。提高沉淀温度和pH值有利于减小晶粒尺寸和降低粉体的热导率。采用相同工艺参数可制备出纯NdMgAl₁₁O₁₉粉体,其晶粒尺寸略大于LaMgAl₁₁O₁₉粉体的尺寸。     

Effects of milling time and calcination condition on phase formation and particle size of lead zirconate nanopowders prepared by vibro-milling

Effect of calcination conditions on phase formation and particle size of lead zirconate (PbZrO₃) powders synthesized by a solid-state reaction with different vibro-milling times was investigated. A combination of the milling time and calcination conditions was found to have a pronounced effect on both the phase formation and particle size of the calcined PbZrO₃ powders. The calcination temperature for the formation of single-phase perovskite lead zirconate was lower when longer milling times were applied. The optimal combination of the milling time and calcination condition for the production of the smallest nanosized (∼28 nm) high purity PbZrO₃ powders is 35 h and 750 °C for 4 h with heating/cooling rates of 30 °C/min, respectively.     

Effect of calcination condition on phase formation and particle size of lead titanate powders synthesized by the solid-state reaction

A perovskite-like phase of lead titanate, PbTiO₃, has been synthesized by a solid-state reaction via a rapid vibro-milling technique. Phase formation of the calcined powders has been investigated as a function of calcination temperature, soaking time and heating/cooling rates by DTA and X-ray diffraction (XRD) techniques. Moreover, morphology and particle size evolution have been determined via SEM technique, respectively. It has been found that single-phase PbTiO₃ powders were successfully obtained for calcination conditions of 550 °C for 4 h or 600 °C for 1 h with heating/cooling rates of 20 °C/min. Higher temperatures clearly favoured particle growth and the formation of large and hard agglomerates.     

Effect of vibro-milling time on phase formation and particle size of nickel niobate nanopowders

A columbite-type phase of nickel niobate, NiNb₂O₆, nanopowder was synthesized by a solid-state reaction via a rapid vibro-milling technique. The effect of milling time on the phase formation and particle size of NiNb₂O₆ powder was investigated. Powder samples were characterized using DTA, XRD, SEM and laser diffraction techniques. It was found that the smallest particle size of 32 nm was achieved at 25 h of vibro-milling after which a higher degree of particle agglomeration was observed on continuation of milling to 35 h. In addition, by employing an appropriate choice of the milling time, a narrow particle size distribution curve was also observed.     

放电等离子体烧结制备Mg85Zn6Y9颗粒增强Mg-9Al-1Zn复合材料组织与力学性能

采用高能球磨法和放电等离子体烧结（SPS）技术,以包含100%长周期堆垛有序结构（LPSO）相Mg₈₅Zn₆Y₉镁合金为原料,通过将其球磨成纳米晶颗粒后与Mg-9Al-1Zn（AZ91）镁合金雾化颗粒进行机械混合,并在350℃烧结温度下成功制备出不同质量分数（0~30wt%）的LPSO相Mg₈₅Zn₆Y₉颗粒增强AZ91复合材料（Mg₈₅Zn₆Y₉/AZ91）。采用光学显微镜（OM）、SEM及TEM对Mg₈₅Zn₆Y₉/AZ91复合材料的微观组织结构进行表征;采用XRD分析其固溶处理前后的相转变;与此同时对复合材料进行显微硬度与压缩试验,综合研究其微观组织与力学性能的关系。相关结果表明,Mg₈₅Zn₆Y₉颗粒经3 h高能球磨后颗粒尺寸显著减小,硬度随晶粒细化而提升。Mg₈₅Zn₆Y₉增强颗粒主要分布在AZ91基体颗粒边界处,随着Mg₈₅Zn₆Y₉质量分数的增加,增强相颗粒有相互结合成连续网格状趋势。增强颗粒与基体界面处未见明显过渡层,基体界面处的β相经400℃×24 h固溶处理后进入基体,部分增强颗粒亦转变为Mg相。本实验条件下制备的最佳性能的20wt% Mg₈₅Zn₆Y₉/AZ91复合材料经固溶处理后的室温屈服强度从200 MPa转变为230 MPa,屈服强度均较未添加Mg₈₅Zn₆Y₉的AZ91镁合金有较大的提高。     

Effect of calcination conditions on phase formation and particle size of Zn3Nb2O8 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 Zn₃Nb₂O₈ powders. The formation of the Zn₃Nb₂O₈ 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 ZnO and Nb₂O₅ precursors and the columbite ZnNb₂O₆ phase tend to form together with the Zn₃Nb₂O₈ phase, depending on calcination conditions. It is seen that optimization of calcination conditions can lead to a single-phase Zn₃Nb₂O₈ in a monoclinic phase.     

Effects of milling time and calcination condition on phase formation and particle size of lead titanate nanopowders prepared by vibro-milling

Effect of calcination conditions on phase formation and particle size of lead titanate (PbTiO₃) powders synthesized by a solid-state reaction with different vibro-milling times was investigated. Powder samples were characterized using XRD, SEM, TEM and EDX techniques. A combination of the milling time and calcination conditions was found to have a pronounced effect on the phase formation and particle size of the calcined PbTiO₃ powders. The calcination temperature for the formation of single-phase perovskite lead titanate was lower when longer milling times were applied. More importantly, by employing an appropriate choice of the milling time and calcination conditions, perovskite lead titanate (PbTiO₃) nanopowders have been successfully prepared with a simple solid-state reaction method.     

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.     

类鱼骨结构CoFe2O4纳米纤维的制备与性能

采用静电纺丝与高温煅烧相结合的方法, 以聚乙烯吡咯烷酮(PVP)、九水合硝酸铁(Fe(NO₃)₃·9H₂O)和六水合硝酸钴(Co(NO₃)₂·6H₂O)为原料, 制备出了类鱼骨结构的CoFe₂O₄纳米纤维, 并研究了煅烧温度对CoFe₂O₄纳米纤维形貌、磁性能以及微波吸收性能的影响。结果表明: 随着煅烧温度的升高, CoFe₂O₄纤维的结晶度和晶粒尺寸逐渐增大, 纳米纤维的表面形貌由光滑发展为粗糙多孔, 煅烧温度超过800 ℃时, 纳米纤维呈现类鱼骨结构; 随着煅烧温度增加纤维直径逐渐减小, 900 ℃煅烧的纤维平均直径为80.3 nm。所制备的纳米纤维经振动样品磁强计(VSM)测试结果表明, 饱和磁化强度(M_s)随着煅烧温度的升高而增加, 在900 ℃煅烧条件下纤维的M_s达87.13 A·m²/kg。矢量网络分析仪测试结果表明, 不同煅烧温度下纤维的微波吸收性能差异明显, 800 ℃下煅烧的纤维具有最佳的吸波性能。CoFe₂O₄纳米纤维通过磁滞损耗和涡流损耗机制吸收电磁波, 煅烧产生的孔洞和类鱼骨形貌有利于电磁波在孔道表面多次反射从而增加反射损耗。     

Raman scattering study on ferroelectric (Ba0.32Sr0.68)2Nb2O7 ceramics

Raman scattering technique was applied to examine the Ba-doping effect to the two low temperature phase transitions of Sr₂Nb₂O₇ (SN) in the temperature range from −190 to 600 °C. The line shape of Raman spectra can be well fitted by multidamped harmonic oscillator model. We did not observe any soft mode related to the two low temperature phase transitions corresponding to those of the pure SN. It is correlated to the disappearance of the incommensurate phase in (Ba_0.32Sr_0.68)₂Nb₂O₇ ceramics. However, the temperature dependence behavior of the three low frequency modes indicates another new structural phase transition around 270 °C. It is considered that the reduction of the interlayer interaction caused by partial replacement of Sr-site by Ba-site, whose ionic radius is larger than that of Sr, may be the reason for the disappearance of the incommensurate phase transition in (Ba_0.32Sr_0.68)₂Nb₂O₇ ceramics.     

Nanocrystallization of SrBi2Nb2O9 from glasses in the system Li2B4O7---SrO---Bi2O3---Nb2O5

Transparent glasses in the system (100−x)Li₂B₄O₇–x(SrO---Bi₂O₃---Nb₂O₅) (10≤x≤60) (in molar ratio) were fabricated by a conventional melt-quenching technique. Amorphous and glassy characteristics of the as-quenched samples were established via X-ray powder diffraction (XRD) and differential thermal analyses (DTA) respectively. Glass–ceramics embedded with strontium bismuth niobate, SrBi₂Nb₂O₉ (SBN) nanocrystals were produced by heat-treating the as-quenched glasses at temperatures higher than 500 °C. Perovskite SBN phase formation through an intermediate fluorite phase in the glass matrix was confirmed by XRD and transmission electron microscopy (TEM). Infrared and Raman spectroscopic studies corroborate the observation of fluorite phase formation. The dielectric constant (_r) and the loss factor (D) for the lithium borate, Li₂B₄O₇ (LBO) glass comprising randomly oriented SBN nanocrystals were determined and compared with those predicted based on the various dielectric mixture rule formalism. The dielectric constant was found to increase with increasing SBN content in LBO glass matrix.     

高容量锂电池负极材料TiNb2O7的合成及其机理

将TiNb₂O₇的前驱体在不同温度(400℃、800℃、900℃、1000℃和1100℃)煅烧,用固相合成法制备TiNb₂O₇负极材料并对其样品进行了TG-DSC、XRD和SEM表征和电化学性能测试。结果表明：在900℃煅烧前驱体,锐钛矿与Nb₂O₅反应的主要产物为Ti₂Nb₁₀O₂₉。Ti₂Nb₁₀O₂₉与金红石反应生成了TiNb₂O₇,生成纯单斜相TiNb₂O₇的最佳条件为在1100℃煅烧6 h。TiNb₂O₇负极材料在0.2C电流密度时初始容量为278.4 mAh/g,初始库伦效率为82.9%。TiNb₂O₇具有良好的倍率容量,在1C循环100次后容量保持率为89%。     

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.     

Al2O3颗粒形貌对注凝成型ZrO2/Al2O3陶瓷性能的影响

采用3种不同形貌的Al₂O₃原料对注凝成型制备ZrO₂/Al₂O₃（ZTA）陶瓷工艺中悬浮体的流变性能进行了研究。以低毒的单体N,N-二甲基丙烯酰胺（DMAA）制备了ZrO₂/Al₂O₃坯体和陶瓷。讨论了3种不同形貌的Al₂O₃原浆料的分散剂用量、球磨时间和固含量对浆料流变性的影响。Al₂O₃粉体呈扁平状有利于降低浆料的黏度,Al₂O₃粉体呈棒状对生坯强度的提高有利。制得的3种ZrO₂/Al₂O₃坯体颗粒间结合紧密,抗弯强度分别达到21.45,19.87,25.90 MPa。Al₂O₃粉体呈颗粒状有利于最终陶瓷力学性能的提高,陶瓷的抗弯强度及断裂韧性分别为680 MPa和7.49 MPa·m^1/2,453.1 MPa和6.8 MPa·m^1/2,549.4 MPa和6.34 MPa·m^1/2。     

Enhanced ferroelectric properties of multilayer SrBi2Ta2O9/SrBi2Nb2O9 thin films for NVRAM applications

Ferroelectric SrBi₂Ta₂O₉/SrBi₂Nb₂O₉ (SBT/SBN) multilayer thin films with various stacking periodicity were deposited on Pt/TiO₂/SiO₂/Si substrate by pulsed laser deposition technique. The X-ray diffraction patterns indicated that the perovskite phase was fully formed with polycrystalline structure in all the films. The Raman spectra showed the frequency of the O–Ta–O stretching mode for multilayer and single layer SrBi₂(Ta_0.5Nb_0.5)₂O₉ (SBNT) samples was 827–829 cm⁻¹, which was in between the stretching mode frequency in SBT (813 cm⁻¹) and SBN (834 cm⁻¹) thin films. The dielectric constant was increased from 300 (SBT) to 373 at 100 kHz in the double layer SBT/SBN sample with thickness of each layer being 200 nm. The remanent polarization (2P_r) for this film was obtained 41.7 μC/cm², which is much higher, compared to pure SBT film (19.2 μC/cm²). The coercive field of this double layer film (67 kV/cm) was found to be lower than SBN film (98 kV/cm).     

Effects of vibro-milling time on phase formation and particle size of Zn3Nb2O8 nanopowders

A monoclinic phase of zinc niobate, Zn₃Nb₂O₈, nanopowder was synthesized by a solid-state reaction via a rapid vibro-milling technique. The effect of milling time on the phase formation and particle size of Zn₃Nb₂O₈ powder was investigated. The formation of the Zn₃Nb₂O₈ phase in the calcined powders has been investigated using DTA and XRD techniques. Morphology, particle size and chemical composition have been determined via a combination of SEM and laser diffraction techniques. It was found that an average particle size was achieved at 20 h of vibro-milling after which a higher degree of particle agglomeration was observed on continuation of milling to 30 h. In addition, by employing an appropriate choice of the milling time, a narrow particle size distribution curve was also observed.     

Polymeric precursor synthesis of Ba2Ti9O20

Ba₂Ti₉O₂₀ was synthesized by Pechini method using citric acid as a chelating agent and ethylene glycol as an esterification agent. The effects, of the pH of the starting solutions and the molar ratio of citric acid to total metal cations concentration on the formation of Ba₂Ti₉O₂₀, were investigated. Increasing the pH of the starting solutions enhances the formation of Ba₂Ti₉O₂₀, but the increase of the molar ratio of citric acid to total metal cations concentration retards the formation of Ba₂Ti₉O₂₀ due to increased diffusion distances. Single-phase Ba₂Ti₉O₂₀ was obtained at 1200 °C for 4 h when the molar ratio of citric acid to total metal cations concentration was unity, regardless of the pH of the starting solutions. Increasing the molar ratio of citric acid to total metal cations concentration up to 2, single-phase Ba₂Ti₉O₂ was synthesized at 1200 °C for 6 h for the precursors with pH 3.5 and 6, but not for the precursors with pH 2.0. DTA, TG, XRD, FT–IR spectroscopy and Raman spectroscopy were used to characterize the precursors and the derived oxide powders. Details of the synthesis and characterizations of the resultant products were given.     

Crystal growth and spectral properties of pure and Co-doped Mg3B2O6 crystal

Novel pure and cobalt-doped magnesium borate crystals (Mg₃B₂O₆) have been grown successfully by the Czochralski technique for the first time. Crystal growth, X-ray powder diffraction (XRD) analysis, absorption spectrum, fluorescence spectrum as well as fluorescence decay curve of Co²⁺:Mg₃B₂O₆ (MBO) were described. From the absorption peaks for the octahedral Co²⁺ ions, the crystal-field parameter Dq and the Racah parameter B were estimated to be 943.3 cm⁻¹ and 821.6 cm⁻¹, respectively. The fluorescence lifetime of the transition ⁴T₁(⁴P) → ⁴T₂ centered at 717 nm was measured to be 9.68 ms.     

M3O4(M=FeCoCrMnMg)高熵氧化物粉体的简易制备及超电容性能研究

高熵氧化物以其独特的结构和潜在的应用前景引起了越来越多的关注。本工作采用简单易行的固相反应法制备了M₃O₄(M=FeCoCrMnMg)高熵氧化物粉体, 采用不同手段对粉体进行表征, 并采用涂覆法制备了 M₃O₄/泡沫镍(M₃O₄/NF)复合电极, 研究其超电容性能。结果表明, 随着煅烧温度升高, Fe₂O₃(H)/Co₃O₄(S)/Cr₂O₃(E)和Mn₂O₃(B)相继固溶进入尖晶石主晶相晶格; 在900 ℃煅烧2 h所得M₃O₄粉体的平均粒径为0.69 μm, 具有单一尖晶石结构(面心立方, Fd-3m, a=0.8376 nm), 且Fe、Co、Cr、Mn和Mg五种元素在晶粒内均匀分布, 呈典型的高熵氧化物特征。此外, M₃O₄/NF复合电极在1 mol/L KOH的电解液中, 当电流密度为1 A·g^-1时, 其质量比电容达到193.7 F·g^-1, 可见M₃O₄高熵氧化物在超级电容器电极材料领域具有良好的应用前景。