Effect of gadolinium content on the thermal volume change of Ba4Na2Nb10O30 − Ba3NaGdNb10O30 solid solutions at ferroelectric phase transition temperature

For sintered samples of Ba₃₊ x Na_1+xGd_1–xNb₁₀O₃₀ (1 x 0), the effect of the addition of gadolinium to barium sodium niobate (BNN,x = 1, tungsten bronze type) was examined by differential scanning calorimetry (DSC) and X-ray powder diffractometry. The volume change (i.e. especially the change ofc-axis length) at the ferroelectric phase transition temperature (T _c< 590 dg C) decreased with the increasing gadolinium content. This result suggests that the addition of gadolinium or other lanthanide elements to BNN is possibly effective to obtain an uncracked single crystal with the Czochralski technique. The DSC indicator method is useful to determine the relative magnitude of volume change atT _c for the same type of sample series, a method which is much easier than the dilatometer method. The relation between the DSC peak area and the volume change of unit cell atT _c is discussed from the thermodynamic viewpoint.     

K4Nb6O17光催化分解水产氢活性的研究

通过高温固相反应法合成了层状K4Nb6O17,采用X射线衍射、比表面积测定、扫描电镜等对K4Nb6O17进行了结构和形貌表征.在I-为电子给体、RuO2为助催化剂的情况下研究了RuO2的负载量、I-离子浓度和溶液pH值对K4Nb6O17光催化分解水产氢活性的影响.研究结果表明,表面负载RuO2可以显著提高K4Nb6O17光催化产氢速度.当I-浓度为15mmol/L,pH=9,RuO2负载量为0.7%时,约400nm紫外光辐射下K4Nb6O17光催化产氢的活性最佳,氢气生成的速度为798.9μmol/L·h.     

硬脂酸法制备层状K2La1.8Nb0.2Ti3O10

采用硬脂酸法在相对较低的温度下掺杂Nb制备了K2La1.8Nb0.2Ti3O10层状化合物.通过X射线衍射、透射电子显微镜、紫外-可见吸收光谱、拉曼光谱对产物进行了表征.结果表明,通过硬脂酸法在800℃可获得超细K2La1.8Nb0.2Ti3O10,颗粒尺寸为100～250 nm,经过Nb掺杂后的产物仍然保持层状结构,层间距约1.5nm.紫外-可见光谱表明掺杂前后的产物在紫外区均有较明显的吸收,但经Nb掺杂后的K2La1.8Nb0.2Ti3O10吸光度明显增强.     

Phase Transitions and Ferroelectric and Superionic Properties of K3Nb3B2O12–K3Nb3Si2O13 Single Crystals

Data are presented on K₃Nb₃O₆(B₂O₆)_1–x (Si₂O₇) _x solid solutions in the K₃Nb₃B₂O₁₂–K₃Nb₃Si₂O₁₃ system. The system is shown to contain two partial solid-solution series in the composition ranges 0 < x< 0.2 (KNB:Si) and 0.8 < x< 1 (KNS:B). KNB:Si crystals are grown from off-stoichiometric melts, and their polymorphism and physical properties are studied. Similar to K₃Nb₃B₂O₁₂, KNB:Si crystals exhibit a complex polymorphism and combine ferroelectric, ferroelastic, and superionic properties. Si substitution for B is shown to have a significant effect on the phase-transition temperatures and electrical properties of K₃Nb₃B₂O₁₂ crystals. The results obtained for K₃Nb₃Si₂O₁₃ crystals demonstrate that, in spite of their hexagonal habit, their room-temperature structure possesses orthorhombic or lower symmetry. The room-temperature dielectric permittivity ₃₃ of K₃Nb₃Si₂O₁₃ crystals is as high as 4000.     

Mössbauer studies of O4+-bombarded Nb3Sn

Mössbauer spectra have been taken for Nb₃Sn films on Hastelloy substrate bombarded with 25-MeV O⁴⁺ ions at fluences of 9.6 × 10¹⁵ and 4.0 × 10¹⁶ cm^–2, and annealed at temperatures up to 1050 C. The bombarded samples are found to contain highly damaged Nb₃Sn and Nb₆Sn₅, and show superconducting transitions at 7.3 and 3.3 K, respectively. Annealing at higher temperatures does not restore the properties of the samples to those known for undamaged Nb₃Sn films. The results rather indicate the presence of Nb₃Sn and also Nb₆Sn₅ even after annealing at 850 C. Annealing at 1050 C seems to produce only regions of heavily damaged Nb₃Sn.On leave from North Dakota State University, Fargo, North Dakota.     

Polymorphism of Ferroelectric, Ferroelastic, Superionic Crystals K3Nb3B2O12 and K3– x Na x Nb3B2O12

Data are presented on the phase transitions and physical properties of K₃Nb₃B₂O₁₂ (KNB) and K_{3 –} Na _x Nb₃B₂O₁₂ (KNNB) crystals. Detailed measurements of the dielectric permittivity, nonlinear optical properties, and electrical conductivity, as well as examination of the domain structure, demonstrate that KNB and KNNB exhibit a complex polymorphism: both have eight different polymorphs between –100 and 900°C. The introduction of Na into KNB raises the transition temperatures, which makes it possible to investigate the low-temperature phases at room temperature. The high-temperature phase transition is antiferroelectric, whereas the other transitions are of a ferroelectric–ferroelastic nature. Along with complex polymorphism, KNB and KNNB exhibit superionic conductivity.     

Ni、Co、Mn、Cu掺杂对K4 Nb6 O17光催化活性的影响

通过高温固相反应合成了铌酸盐K4Nb6O17及Ni2 、Co3 、Mn4 、Cu2 (5.0%mol)掺杂的K4Nb6O17并采用X射线衍射、紫外可见漫反射光谱、扫描电镜、比表面积分析等对其进行了结构和形貌表征.在甲醇为电子给体、Pt为助催化剂的情况下,研究了K4Nb6O17及Ni2 、Co3 、Mn4 、Cu2 掺杂的K4Nb6O17作为催化剂在约400nm紫外辐射下分解水产氢的光催化活性,并讨论了引起催化剂活性差异的原因.     

Sol—Gel法合成K（Ta,Nb）O3材料

以金属醇盐乙醇钾［Ｋ（ＯＣ２Ｈ５）］，乙醇铌［Ｎｂ（ＯＣ２Ｈ５）５］和乙醇钽［Ｔａ（ＯＣ２Ｈ５）５］为原料，用Ｓｏｌ－Ｇｅｌ法合成了Ｋ（Ｔａ，Ｎｂ）Ｏ３超细粉末和薄膜，研究了工艺参数如前驱体溶液浓度、热处理温度等因素对材料结构及物性的影响。粉料的粒径为２０￣４０ｎｍ，所需合成温度约为７００℃，比通过传统的固相反应制备同种材料的合成温度低近１００℃；以ＳｒＴｉＯ３（１００）单晶作基片，采用匀胶法获得     

Synthesis of Double Uranyl Phthalates of the M4[(UO2)4(μ3-O)2(C6H4C2O4)4] ⋅ nH2O Type with M = NH4, K, and Cs. Crystal Structure of K4[(UO2)4O2(C6H4C2O4)4] ⋅ 3H2O

Double U(VI) phthalates with NH ₄ ⁺ , K⁺, and Cs⁺ ions in the outer sphere were synthesized. The X-ray phase analysis shows that their structures are similar. Single crystals were prepared and the structure of K₄[(UO₂)₄(μ₃-O)₂(C₆H₄C₂O₄)₄] ? 3H₂O was solved. In the [(UO₂)₄O₂(C₆H₄C₂O₄)₄]^4? anions forming the main structural motif, each bridging oxygen atom μ₃-O combines one pentagonal and two hexagonal bipyramids, which, in turn, are combined in centrosymmetrical tetramers. The phthalate ions have coordination capacity equal to 3; each ligand coordinates U(1) in the bidentate fashion via one carboxy group and U(2) in the bidentate fashion to form a planar seven-membered chelate ring.     

Influence of Nb2O5 on the varistor behavior of TiO2–Cr2O3 system

This work investigated the influence of Nb₂O₅ dopant on the varistor behavior of the ternary system (99.95 ? x)%TiO₂, 0.05 %Cr₂O₃, x%Nb₂O₅, where x = 0.10; 0.15; 0.20; 0.25 % in mol. The processing was carried out using the conventional oxide mixture method. The initial oxides were homogenized in alcoholic media in a ball mill, for 3 h, dried in oven and isostatically pressed at 210 MPa and sintered at 1,400 °C for 2 h in air atmosphere and cooled at 5 °C/min cooling rate, resulting in pellets with high densification. Electrical measurements in continuous current at different temperatures revealed that for the lowest Nb₂O₅ concentration the breakdown electric field, E_B = 4.41 V/cm and non-linear coefficient, α = 4.6 were obtained, and for the highest Nb₂O₅ concentration the breakdown electric field, E_B = 9.71 V/cm and non-linear coefficient, α = 15.3 were obtained. These low values in the breakdown electric field enable these varistor systems to be used in protection systems for low-voltage energy grids. Changes in the potential barrier present in the grain–grain boundaries could also be observed, in which the height increased and the width decreased with the increase in the dopant concentration. However, for x = 0.25 % in mol Nb₂O₅, a significant reduction in the potential barrier height and the voltage per barrier was obtained. Furthermore, the tendency to increase the volume of the unitary cell with the increase of dopant concentration, which was interrupted in the system with 0.25 % Nb₂O₅, was another evidence that suggested the occurrence of Nb₂O₅ segregation in the grain boundaries, or even that the reduction in the average grain size could possibly dilute Nb₂O₅ concentration in the grain boundaries. The average grain size was calculated through SEM micrographs and ranged from 7 to 16 μm, with larger sizes occurring for lower dopant concentrations and presenting higher porosity and lower uniformity in the grains shape.     

高性能(Na0.51K0.44Li0.05)Nb0.92Ta0.08O3-Na5.4Cu1.3Sb10O29无铅压电陶瓷

采用传统的氧化物固溶工艺制备了（Na0.51K0.44Li0.05）Nb092Ta0.08O3和助烧剂Na5.4Cu13Sb10O29.对（Na0.51K044Li0.05）Nb0.92Ta0.08O3添加助烧剂Na5.4Cu1.3Sb10O29的研究表明,助烧剂能大幅度提高（Na0.51K0.44Li0.05）Nb0.92Ta0.08O3的压电和机电耦合性能.质量百分比为4%Na5.4Cu1.3Sb10O29掺杂的（Na051K0.44Li0.05）Nb092Ta0.08O3具有高的压电应变常数（d33=266pC/N）,高的机电耦合系数kt（46.7%）、k33（63.7%）,较低的损耗（tanδ=1.8%）,和高的居里温度（391℃）.这些参数表明,Na5.4Cu1.3Sb10O29掺杂的（Na0.51K0.44Li0.05）Nb0.92Ta0.08O3是替代锆钛酸铅且具有很好的应用前景的无铅压电陶瓷.     

Piezoelectric properties of Nb2O5 doped and MnO2—Nb2O5 co-doped Pb(Zr0.53Ti0.47)O3 ceramics

The effects of Nb₂O₅ addition and MnO₂Nb₂O₅ co-addition on the piezoelectric properties of Pb(Zr_0.53Ti_0.47)O₃ (PZT) ceramics are investigated. When Nb₂O₅ is added to PZT, the planar coupling factor (K _p) significantly increases but the mechanical quality factor (Q _M) as well as the electrical quality factor (Q _E) decreases. When MnO₂ and Nb₂O₅ are co-doped, Q _M increases remarkably while K _p rarely changes. This increase in Q _M is ascribed to the domain pinning by Mn as is the case of previously reported MnO₂-doped PZT, and the negligible change in K _p is ascribed to the barely changed tetragonality. Even though MnO₂-Nb₂O₅ co-doped PZT shows a smaller induced strain than that of Nb₂O₅- doped PZT, excellent temperature stability is obtained. It is shown that MnO₂Nb₂O₅ co-doped PZT may be a very suitable material for high-power piezoelectric actuators because of its high K _p, Q _M and Q _E, its low dielectric constant and its excellent temperature stability.     

Improved microwave dielectric properties of Mg4Nb2O9 ceramics with CaO–B2O3–SiO2 glass additions

The effects of CaO–B₂O₃–SiO₂ (CBS) glass addition on the sintering temperature and dielectric properties of Mg₄Nb₂O₉ ceramics have been investigated using X-ray diffraction, Scanning electron microscopy and Differential thermal analysis. The CBS glass can change to liquid phase at about 750 °C and a small amount of CBS glass addition to Mg₄Nb₂O₉ ceramics can greatly decrease the sintering temperature to about 1,125 °C. It is revealed that the reduced sintering temperature is attributed to the formation of liquid phase. The major phases of the sample are Mg₄Nb₂O₉ and MgNb₂O₆. The relationship between τ _f values and the content of glass additions have the reverse change trends. The Mg₄Nb₂O₉ ceramics with 2wt% glass addition sintered 1,125 °C exhibit good microwave dielectric properties: dielectric constant (ε _r ) of 13 and Q·f value of 69,000 GHz.     

Dielectric properties and high-temperature dielectric relaxation of Ba4Gd2Fe2Nb8−xTaxO30 ceramics

Several ferrum oxides of formula Ba₄Gd₂Fe₂Nb_8?xTa_xO₃₀ (x = 2, 4, 6 and 8) with tetragonal tungsten-bronze structure have been synthesized by the conventional solid state sintering method. Dielectric response of the samples was studied using AC impedance spectroscopy and universal dielectric relaxation law in detail. The dielectric anomaly at high temperature is attributed to the mobility of oxygen vacancies. Arrhenius activation energy associated with the migration of oxygen vacancies is estimated from impedance spectroscopy, which is 0.77, 1.11, 1.26 and 1.02 eV for x = 2, 4, 6 and 8, respectively.     

掺SrLi1／4Nb3／4O3的SrTiO3缺陷化学研究

利用Ｈ２／Ｈ２Ｏ体系获得不同的氧分压,上电极法 掺杂ＳｒＬｉ１／４Ｎｂ３／４Ｏ３的ＳｒＴｉＯ３瓷体在８００－１２００℃,Ｐｏ２＝１０＾１７－１０＾５Ｐａ的电导率。通过ｌｏｇＰｏ２－ｌｏｇσ图,计算出半导化活化焓约为２８７．７ｋＪ／ｍｏｌ,讨论了ＳｒＬｉ１／４Ｎｂ３／４Ｏ３掺杂的ＳｒＴｉＯ３在不同氧分压区域的主ｎ型半导体化向ｐ型半导化转变的特点。     

K（Ta,Nb）O3薄膜中钙钛矿相的形成机理研究

研究了工艺参数和衬底材料对Ｋ（Ｔａ，Ｎｂ）Ｏ３薄膜生长的影响，研究表明钙钛矿相由焦绿石中间相转变而成，热处理时低速升温同样可以获得纯钙钛矿相的Ｋ（Ｔａ，Ｎｂ）Ｏ３薄膜，分析了（１００）ＳｒＴｉＯ３，（１００）ＭｇＯ单晶衬底上钙钛矿相的形成机理，并解释了在硅单晶和石英玻璃衬底上纯钙钛矿结构的Ｋ（Ｔａ，Ｎｂ）Ｏ３薄膜不易形成的原因。     

Influence of processing on the microstructure of Cu–8Cr–4Nb

The particle-strengthened Cu–8 at.%Cr–4 at.%Nb alloy is processed by consolidation of atomized powders followed by extrusion to obtain bars and rolling to produce sheets. Comparison of copper matrix grain and second-phase particle structures in both extruded and rolled Cu–8Cr–4Nb was performed. Extruded material displayed locally banded arrangements of Cr₂Nb particles, while the distribution of particles was more uniform in rolled material. Mean Cr₂Nb particle sizes were found to be essentially the same for both processing methods. Non-spherical particles in the extruded alloy showed some preferred orientation, whereas the rolled material displayed a more uniform particle orientation distribution. Extruded material exhibited a dual grain size distribution with smaller grains in banded regions. The mean grain size of 1.36 μm in extruded material was larger than the 0.65 μm grain size of rolled material. A [101] texture was evident in extruded material, whereas the rolled material was only slightly textured along the [001] and [111] directions. The processing differences for the rolled and extruded forms give rise to different microstructures and hence higher creep strength for the extruded material in the temperature range of 773–923 K.

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佳能发布30英寸IPS面板4K超高清监视器

2013年11月7日．佳能发布了30英寸专业视频监视器DP—V3010．正式宣布进入专业4K视频监视器市场。