Magnetic and electronic properties of nanocrystalline Gd3Fe5O12 garnet

The Gd₃Fe₅O₁₂ nanocrystalline Gadolinium Iron Garnet (GdIG) obtained from a sintered block was milled in a high energy ball mill. We measured the magnetization at 5 K under applied fields up to 12 T. We report here our study of approach to saturation magnetization. The results have been interpreted within the framework of random anisotropy model. From an analysis of the approach to saturation magnetization some fundamental parameters have been extracted. We have determined the anisotropy field H_r and the local magnetic anisotropy constant K_L. In addition, first-principles spin-density functional calculations, using the Full potential Linear Augmented Plane Waves (FLAPW) method are performed to investigate electronic and magnetic structures. All computed parameters are discussed and compared to available experimental data.     

Electrochemical corrosion behavior of nanocrystalline zinc coatings in 3.5% NaCl solutions

The corrosion behavior of electrodeposited nanocrystalline (NC) zinc coatings with an average grain size of 43 nm was investigated in 3.5% NaCl solutions in comparison with conventional polycrystalline (PC) zinc coatings by using electrochemical measurement and surface analysis techniques. Both polarization curve and electrochemical impedance spectroscopy (EIS) results indicate that NC and PC coatings are in active state at the corrosion potentials, and NC coatings have much higher corrosion resistance than PC ones. The corrosion products on both coating surfaces are mainly composed of ZnO and Zn₅(OH)₈Cl₂·H₂O, but the corrosion products can form a relatively more protective layer on NC coating surfaces than on PC coatings. The EIS characteristics and corrosion processes of PC and NC zinc coatings during 330 h of immersion were discussed in detail.     

Phase transformations in nanocrystalline TiO2 milled in different milling atmospheres

The structural evolution of nanocrystalline TiO₂ milled in different milling atmospheres was studied by X-ray diffraction (XRD), Raman spectroscopy and X-ray photoelectron spectroscopy. Rietveld refinements of the XRD data showed that high-energy ball milling induced the transformations from anatase to srilankite and rutile at room temperature and ambient pressure. The milling atmospheres with different oxygen partial pressures had an influence on the transformation kinetics of anatase. When the nanocrystalline TiO₂ powders were, respectively, milled in oxygen, air and nitrogen atmospheres, the transformation rates of anatases in turn increased with a decrease in oxygen partial pressure of the milling atmosphere, due to the reducing concentration of oxygen vacancies in the milled TiO₂ lattice.     

Rational Fabrication of Size Tunable SnO2 Hollow Microspheres

A designed solution route was developed to fabricate size tunable SnO₂ hollow microspheres based on the sol-gel theory. The hydrolysis of SnSO₄ released protons to form SnO₂ particulates and induced the decrease of pH value. To minimize the high surface energy, the SnO₂ particulates tended to assemble into large particles, the size of which was affected by the electrolyte concentration or pH value. Elevating SnSO₄ content aroused the decrease of the pH value that directed to the shrinkage of the aggregated particle size of SnO₂. Size tunable SnO₂ hollow microspheres were then rationally fabricated under solvothermal conditions via Ostwald ripening by simply adjusting the SnSO₄ concentration. The in situ pH decrease directed to the shrinkage of the particle size from 270 nm to 112 nm. The formation mechanism was confirmed and rationally elucidated by the time dependant morphology evolution. Charge-discharge tests revealed that the reduced particle size aroused an improved lithium ion battery performance.     

Rare-earth iron-based intermetallic compounds and their carbides: Structure and magnetic behaviors

The structural and magnetic properties of Sm₂Fe_17-xMo_x, its out of equilibrium precursor SmFe_9-yMo_y and their carbides are investigated by means of powder X-ray diffraction, magnetic measurements and high-resolution transmission electron microscopy. The structure of the nanocrystalline Sm_1-s(Fe,Mo)_5+2s alloys are governed by the s Sm vacancy rate and the x amount of Mo. In this work, the Rietveld analysis shows that for s=0.33 the structure is of Th₂Zn₁₇-type and P6/mmm with the stoichiometry 1/9 for s=0.36. Moreover, it points out a lattice expansion along the c-axis after Mo substitution for Fe and reveals a 6c preferential occupation for Mo atoms in structure, and 2e for the out of equilibrium hexagonal precursor. Upon carbon insertion, the lattice expansion favors the Curie temperature increase up to 35% for Sm₂Fe_16.42Mo_0.58C₂ and 49% for the metastable SmFe_8.7Mo_0.3C carbide. The Curie temperature and the coercive field of the 1/9 carbides are higher than those of 2/17 ones. This makes the out of equilibrium hexagonal precursor a competitive candidate for use as permanent magnet.     

Chemical synthesis of nanocrystalline SnO2 thin films for supercapacitor application

Nanocrystalline SnO₂ thin films were deposited by simple and inexpensive chemical route. The films were characterized for their structural, morphological, wettability and electrochemical properties using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy techniques (SEM), transmission electron microscopy (TEM), contact angle measurement, and cyclic voltammetry techniques. The XRD study revealed the deposited films were nanocrystalline with tetragonal rutile structure of SnO₂. The FT-IR studies confirmed the formation of SnO₂ with the characteristic vibrational mode of Sn-O. The SEM studies showed formation of loosely connected agglomerates with average size of 5-10 nm as observed from TEM studies. The surface wettability showed the hydrophilic nature of SnO₂ thin film (water contact angle 9°). The SnO₂ showed a maximum specific capacitance of 66 F g⁻¹ in 0.5 Na₂SO₄ electrolyte at 10 mV s⁻¹ scan rate.     

Controlled synthesis, characterization and optical properties of CdS nanocrystalline thin films via chemical bath deposition (CBD) route

In this study, the CdS nanocrystalline thin films obtained from an ammonia-free chemical bath deposition process. The crystallites with a size range of 10–20 nm in diameter with zinc blend (cubic) and wurtzite (hexagonal) crystal structure and strong photoluminescence were prepared from the mixture solutions of: cadmium chloride dihydrate as a cadmium source, thiourea as a sulfur source and sodium citrate dihydrate as a complexing agent for cadmium ions. The well-cleaned glass used as a substrate for thin films deposition. The obtained samples were characterized by the techniques such as scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectra (XPS), atomic force microscopy (AFM) and fluorescence spectroscopy. Also, the effect of two parameters such as pH and temperature of reaction on the synthesis of CdS nanocrystals was studied. Finally, it was found the CdS nanocrystals showed sharp excitation features and strong “band-edge” emission.     

ICF物理实验用纳米Cu块体靶材的制备研究

 采用自悬浮定向流法制备了金属纳米粉体并采用真空手套箱专利技术和冷压法在高压（1.5 GPa）作用下保压40 min后，成功制备出了相对密度达97％和显微硬度达1.85 GPa的金属Cu纳米晶材料。经XRD分析，其晶粒大小为20 nm。正电子湮没(PAS)实验结果表明，其空隙大小和数量与采用惰性气体冷凝法原位压制(IGC)的样品相比，空位簇数量较多，微空隙的大小和数量基本相当。激光惯性约束聚变（ICF）模拟实验表明：采用该方法制备的纳米Cu块体材料靶的激光转换效率比常规Cu材料靶高5倍。     

纳米晶ZrO2∶Dy3+的制备与发光性质研究

利用共沉淀法制备了纳米晶ZrO2∶Dy3+发光粉体,对不同掺杂浓度、不同煅烧温度的系列样品,均观测到Dy3+离子的室温强特征发射.样品的晶相与发射性质的研究表明:所制备的样品经600℃~950 ℃热处理后,晶相经历从四方相到以单斜相为主的变化;由于晶相的变化,发现有两个发光中心,分别位于四方相和单斜相.激发Dy3+的6P7/2能级,当稀土离子处在四方相(格位一)时有利于483 nm和583 nm的发射,当稀土离子处在单斜相(格位二)时有利于490 nm和577 nm的发射.基质ZrO2和Dy3+离子之间有能量传递,950℃时能量传递效果最好.荧光强度与掺Dy3+离子浓度关系表明,Dy3+在纳米晶ZrO2中的最适合掺杂浓度与ZrO2的晶相有关,四方相时,最适合掺杂浓度为0.5%,混合相时为1%.