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1.
Single crystals of Perovskite-type oxide BaPb 1−xBi xO 3 are grown from BaCO 3-PbO 2-Bi 2O 3 solutions which are weighed in two kinds of mixing ratios: X/2 mol % BaCO 3 − (100− X) mol % PbO 2 − X/2 mol % Bi 2O3 and (10+ X/2) mol % BaCO 3 − (90− X) mol % PbO 2 − X/2 mol % Bi 2O3 These room temperature crystal structures are examined by using an X-ray powder diffraction method. The crystals grown from X/2−(100− X)− X/2 mol % solutions are orthorhombic at room temperature, while the structures are tetragonal with crystals grown from relatively Ba rich and Pb poor ( (10+ X/2)−(90− X)− X/2 mol % ) solutions. This result indicates that the difference in the mixing ratio of the initial materials brings about a drastic structural change. The orthorhombic and the tetragonal crystals of x0.25 exhibit superconducting transition at 10K and 12K, respectively. The transition temperature in the latter is 2K higher than the former. In the light of this result, some difference between orthorhombic and tetragonal crystals is considered to influence superconductivity in this system. 相似文献
2.
Barium hexaferrite (phase M) samples with different nanostructures were studied. Sample M1 is composed of nanocrystals of BaFe 12O 19 produced after milling the elemental oxides (Fe 2O 3 and BaCO 3) and heating in air atmosphere. Two more samples were produced by milling the same oxides and a 20% excess of -Fe. The resulting powder (composed of phase M and a 20% hematite) was heat-treated in different conditions, resulting in samples MF1 (with a partially sintered structure) and MF8 (with almost completely sintered structure). In order to have an insight into the interactions in each sample, Preisach distributions were obtained using first-order reversion curves (FORCs) measurements. The Preisach distribution corresponding to M1 is a Gaussian-shaped one, with a maximum around 4.1 kOe. The distribution of MF1 has a narrow and high peak at 5.3 kOe, a number of overlapping small peaks down to 2.6 kOe and a distinct and low-intensity peak at 2 kOe. MF8 has a Preisach distribution with a succession of equally spaced distinct peaks from 4.2 to 1.5 kOe. The found Preisach distributions suggest that the interactions occur among nanocrystals inside conglomerates with different number of particles. 相似文献
3.
以Eu 2O 3、NH 4H 2PO 4、BaCl 2·2H 2O、BaCO 3为原料,用高温固相法制备出Ba 5(PO 4) 3Cl:Eu 2+荧光粉。用XRD衍射仪和荧光分光光度计分别测试样品的物相结构和荧光性能。结果表明:制备得到的Ba 5(PO 4) 3Cl:Eu 2+为单相,在245~425 nm范围均有较大吸收,具有最强峰在435 nm的窄带发射。该荧光粉的发光强度受Eu 2+浓度的影响较大,其发光随着Eu 2+浓度的增加先增强后减弱。当Eu 2+摩尔分数为3%时,发光强度达到最大。 相似文献
4.
以高温固相法成功合成了一系列Eu 3+离子激活Ba 3WO 6红色荧光粉。分别采用X射线衍射(XRD)和荧光光谱(FL)对样品的晶体结构和发光性能进行了表征。结果表明,样品均具有立方晶系的双钙钛矿结构;Eu 3+离子的激发谱由一个宽带(包括Eu 3+-O 2-和W 6+-O 2-电荷转移带)和若干个窄峰(4f-4f电子跃迁)组成,而跃迁 5D 0→ 7F 1和 5D 0→ 7F 2则构成了发射谱的主要部分。调整原材料中BaCO 3和WO 3的量的比,XRD的主衍射峰位发生红移至与标准谱完全吻合,发光强度有所提升并分析了原因。Eu 3+离子的临界摩尔分数为0.05,临界距离(R c)为1.263 4 nm。在314 nm或394 nm激发光下,样品发出红光(λ max=596 nm),色坐标为(0.618,0.342),在LED照明、显示等领域具备一定潜力。 相似文献
5.
以BaCO_3、SiO_2、Eu_2O_3为原料在还原气氛下采用高温固相法制备了Ba_3SiO_5∶Eu荧光粉体。实验结果表明,制备Ba_3SiO_5的最佳工艺条件是Ba/Si比为3,1 200℃保温4 h。光谱分析表明,Ba_3SiO_5∶Eu荧光粉在254,365,410 nm激发下发射主峰为566 nm(Eu~(2+)的4f~n~(-1)5d→4f~n)宽带发射,量子效率分别为70%、50%、10%,荧光寿命为百纳秒级;以566 nm为监视波长测得激发谱为主峰在250~450 nm范围内的宽带发射,主峰为360 nm,且在410 nm出现小峰; Eu离子最佳掺杂浓度为5%,由发光强度随掺杂离子浓度变化曲线,可以得出Ba_3SiO_5中Eu离子能量传递是基于电四级-电四级作用。 相似文献
6.
本实验以氯化铜 (CuCl 2·2H 2O) 和二硫化碳(CS 2)为原料, 以乙二醇(C 2H 6O 2) 为溶剂, 通过溶剂热法成功制备了具有可见光活性的花状硫化铜(CuS) 级次纳米结构. 并利用X射线粉末衍射技术(XRD)、扫描电子显微镜(SEM)、透射电子显微镜(TEM) 等技术对其进行了表征, 利用紫外可见吸收光谱(Uv-vis)分析了其光学性能, 并以甲基橙为目标降解物对其可见光催化活性进行了研究. 结果表明: 花状CuS级次纳米结构具有很高的可见光催化活性, 与体相CuS粉末相比有很大的提高, 在自然光照射下对甲基橙的降解率可以达到100%. 同时本文对花状级次纳米结构的形成机理进行了分析.
关键词:
硫化铜
溶剂热
级次纳米结构
光催化 相似文献
7.
Degradation processes in 2212 thallium-based superconductors have been investigated using X-ray diffraction and electron microscopy techniques. It has been shown that the formation of amorphous or microcrystalline material by decomposition of the superconducting phase is followed by the crystallization of BaCo 3 and other oxide compounds. The influence of preexisting BaCO 3 on the rate of this degradation process has also been studied, and the results indicate that the removal of this stable precursor compound is an important step in improving the long term stability of the 2212 phase. 相似文献
8.
采用油酸盐法分别制备出均匀的上转换发光裸核纳米粒子及其包覆具有不同Yb 3+浓度掺杂的NaYF 4:Yb 3+,Er 3+核壳纳米结构的上转换纳米粒子。在不同温度下(90~450 K),研究分析了在壳中掺杂不同浓度Yb 3+的NaYF 4:Yb 3+,Er 3+@NaYF 4:x%Yb 3+核壳纳米体系的上转换发光特性。结果表明:在NaYF 4:Yb 3+,Er 3+上转换体系中,惰性壳中的525 nm( 2H 11/2 → 4I 15/2)发射峰呈现出与活性壳中不一样的趋势。壳层中掺杂的Yb 3+通过声子对纳米粒子内部发光与表面及外界之间的相互作用起到了重要的"桥"连作用。 相似文献
9.
We explore the photoluminescence properties of zinc silicate (Zn 2SiO 4) nanostructures synthesized by vapor-liquid-solid (VLS) mode of growth using three different catalysts (Sn, Ag, and Mn). Different catalysts significantly influence the growth rate which in turn has an impact on the structure and hence the photoluminescence of the prepared zinc silicate nanostructures. Zn 2SiO 4 has a wide bandgap of about 5.5 eV and in its pure form, it does not emit in visible region due to its inner shell electronic transitions between the 3d 5 energy levels. However, the incorporation of different catalysts (Sn, Ag and Mn) at different growth temperatures into the Zn 2SiO 4 crystal growth kinetics provides wide visible spectral range of photoluminescence (PL) emissions. PL analysis shows broad multi-band spectrum in the visible region and distinct colors (red, yellow, green, blue, cyan and violet) are obtained depending on the crystalline structure of the prepared nanostructures. The allowed transitions due to the effect of different catalysts on zinc silicate lattice offer a huge cross-section of absorption that generates strong photoluminescence. The correlation between the structural and optical properties of the synthesized nanostructures is discussed in detail. The synthesized photoluminescent nanostructures have potential applications in solid-state lighting and display devices. 相似文献
10.
The optical response of excitons confined in characteristic nanostructures in layered metal tri-iodide crystals introduced by some irregular stackings from the bulk structures is reviewed. In BiI 3 a specific stacking fault takes place during crystal growth constructing macroscopic planar defects. In this space conspicuous localized exciton transitions occur below the intrinsic absorption edge. Another stacking disorder introduced by applying external stress in this crystal brings about a new nanostructure domain of symmetry D 3d different from that of bulk symmetry C 23i. The optical transitions due to new structures appear in the lower energy region as an absorption and luminescence line series. The similar nanostructures are induced in SbI 3 crystals under the hydrostatic pressure. In these nanostructures, the electronic structure is analyzed by a model based on the confined excitons in a nanoscale disk-like shape space. The magnetic field effect confirms the structure in the wave function-size scale. The nanoscale disk-like structure of BiI 3 in CdI 2 matrices is also obtained by a hot wall technique and mixed crystal annealing, which is realized by observing the size distribution with an electron microscope. In a BiI 3 disk in CdI 2 Stokes shifted photoluminescence bands appear. The Stokes shifts of the luminescence bands are understood by considering the size-dependent exciton-phonon interaction. In these nanostructures large optical nonlinearity under the intense laser field was obtained. 相似文献
11.
分别选用四种不同阴离子的镍、钴金属盐作为镍源和钴源,通过简单的水热法合成镍钴双金属氢氧化物,并对双金属氢氧化物的形貌结构及其电化学性能进行表征分析,以研究镍源和钴源阴离子的种类对所得材料形貌结构及其电化学性能的影响.结果表明:不同的镍、钴金属盐不仅影响着双金属氢氧化物的形貌结构,而且对其电化学性能也有很大的影响,其中,以硫酸镍和硫酸钴合成的镍钴双金属氢氧化物具有片层形貌结构和优异的电化学性能,在电位窗口为0.45 V、电流密度为1 A/g时,其比电容值可达1551 F/g. 相似文献
12.
对于稀土离子掺杂的上转换发光,由于稀土离子吸收截面小、吸收范围窄,导致其发光强度受限.最近,在稀土上转换纳米粒子的表面连接近红外染料分子敏化发光,被证实是提高上转换发光强度的有效策略.然而,将染料分子连接经典的稀土Yb掺杂纳米粒子,并不能有效利用染料分子的敏化能力.针对这一问题,本文通过高温热分解法成功制备了Nd3+敏... 相似文献
13.
Novel systems based on colloidal magnetic nanocrystals (NCs), potentially useful as superparamagnetic (SP) contrast agents for magnetic resonance imaging (MRI) have been investigated. The NCs we have studied comprise organic-capped single-crystalline maghemite (γ-Fe 2O 3) cores possessing controlled sizes and shapes. We have comparatively examined spherical and tetrapod-like NCs, the latter being branched particles possessing four arms which depart out at tetrahedral angles from a central point. The as-synthesized NCs are passivated by hydrophobic surfactant molecules and thus are fully dispersible in nonpolar media only. The NCs have been made soluble in aqueous solution by applying a procedure based on the surface intercalation and coating with an amphiphilic polymer shell. NMR relaxivities R1 and R2 were compared with ENDOREM ®, one of the standard commercial SP-MRI contrast agent. We found that the spherical NCs exhibit R1 and R2 relaxivities slightly lower than those of ENDOREM ®, over the whole frequency range; on the contrary, tetrapods show relaxivities about one order of magnitude lower. The physical origin of such difference in relaxivities between tetrapod- and spheres-based nanostructures is under investigation and it is possibly related to different sources of the magnetic anisotropy. 相似文献
14.
采用高温固相合成法制备出BaSi 2O 5:Pb 2+荧光体。考察了BaF 2的加入量对产物紫外发射强度的影响。用差示扫描量热分析,X射线衍射,光致发光光谱研究了掺入助熔剂BaF 2后BaSi 2O 5:Pb 2+紫外发射强度显著增强的机理,并从热力学角度对实验结果作了分析。研究表明少量BaF 2的掺入加快了反应速度;降低了BaSi 2O 5:Pb 2+形成温度,在高温下与SiO 2反应生成SiF 4气体,生成的SiF 4再与BaCO 3反应形成结晶良好的BaSi 2O 5:Pb 2+荧光体。 相似文献
15.
以硝酸锶[Sr(NO 3) 2]和结晶四氯化锡(SnCI 4·5H 2O)为原料,有机碱四甲基氢氧化铵[N(CH 3) 4OH]为矿化剂,采用共沉淀法制备SrSnO 3纳米粒子。用XRD和IR对样品的物相和结构进行表征,并研究了对亚甲基蓝废水的光催化降解性能。结果表明:用该法在500℃煅烧1h时制备的纯立方相SrSnO 3纳米晶粒在可见光照下具有良好的光催化性能。催化剂浓度为60mg/L,反应时间为100min时,降解率可达94%。 相似文献
16.
Among all the known electrode materials, vanadium pentoxide (V 2O 5) has high reversible capacity. It is a very valuable material for research of the complexity, rich structure and morphology. However, it also has some disadvantages, such as poor cycle stability, low discharge voltage, low conductivity and Li + diffusion coefficient. In this regard, researchers have carried out a lot of research, such as using various methods to improve the nanostructures, introducing heterostructures, introducing point defects or cation doping in the crystal structure, etc. The electrochemical performance of V 2O 5 has been significantly improved in reversible capacity, high-rate capacity and long-term cycle stability. In this paper, V 2O 5 based nanostructure with different chemical composition are briefly introduced, and it covers V 2O 5 nanomaterials with different morphology, including 1D nanorods, nanobelts, nanotubes, 2D leaf like nanosheets and other nanosheets, and 3D hollow structures, porous nanostructures, porous eggshell microsphere structures. The composite nanomaterials of V 2O 5 and different carbonaceous supports are also introduced. Finally, the V 2O 5 composite materials doped with cations are discussed. The electrochemical performance of V 2O 5 based electrode can be improved effectively by obtaining appropriate nanostructure and optimized chemical composition. 相似文献
17.
The present study involves co-precipitation method to grow un-doped and Zr-doped bismuth iron oxide with x_(Zr)=0.10–0.30. The molar solutions of ferric chloride(FeCl_3), zirconyle chloride(ZrOCl_2), and bismuth chloride(BiCl_3) are prepared in distilled water, and are allowed to react with sodium hydroxide(Na OH). The synthesized powders are then converted into pellets, which are sintered at 500℃ for two hours in a muffle furnace. X-ray diffraction(XRD) shows multi-phase formation in un-doped and Zr doped samples. Scanning electron microscope(SEM) depicts layered structure at low Zr concentration x_(Zr)= 0.10, while uniform surface with smaller grains and voids is observed at x_(Zr)= 0.20, but at x_(Zr)= 0.30, cracks and voids become prominent. The ferromagnetic nature of the un-doped sample is observed by vibrating sample magnetometer(VSM), while paramagnetic behavior appears due to Zr doping. The ferromagnetism in un-doped sample is lost by Zr doping, which is due to the formation of additional Fe–O–Zr bonds that induce paramagnetic behavior. 相似文献
18.
Magnetic interactions in hexaferrite samples of Ba1-xLax+δFe12-xCoxO19 composition were studied. The precursor powders—barium carbonate (BaCO3), lanthanum oxide (La 2O 3), hematite (Fe 2O 3) and cobalt acetate—were milled for 100 h in air atmosphere and heat-treated for 1 h at . The structural characterization was performed by X-ray diffraction. The FORC distributions show a single peak at high switching fields, indicating that the substituted systems are formed by weakly interacting particles. La excess induces the decoupling of the particles. 相似文献
19.
Mechanochemical effects on the formation of Mg---O---Ti complex and microwave dielectric properties of MgTiO 3 oxides were studied using several different starting materials. Single phase MgTiO 3 powder was obtained after heating (900 °C, 2 h) the mechanically activated precursor from a mixture of two unitary powders, magnesium hydroxide and anatase (MP). Formation of MgTiO 3 on subsequent thermal treatment was significantly accelerated by incipient mechanochemical interaction. The Q value of the ceramics sintered at 1350 °C for 2 h from MP was higher than those of three other ceramics due to the uniformity of the microstructure and phase. 相似文献
20.
The unique plasmon resonance characteristics of nanostructures based on metal clusters have always been the focus of various plasmon devices and different applications. In this work, the plasmon resonance phenomena of polyhedral silver clusters under the adsorption of NH 3, N 2, H 2, and CH 4 molecules are studied by using time-dependent density functional theory. Under the adsorption of NH 3, the tunneling current of silver clusters changes significantly due to the charge transfer from NH 3 to silver clusters. However, the effects of N 2, H 2, and CH 4 adsorption on the tunneling current of silver clusters are negligible. Our results indicate that these silver clusters exhibit excellent selectivities and sensitivities for NH 3 detection. These findings confirm that the silver cluster is a promising NH 3 sensor and provide a new method for designing high-performance sensors in the future. 相似文献
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