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排序方式: 共有3038条查询结果,搜索用时 15 毫秒
1.
《Ceramics International》2022,48(9):12281-12290
Following the rapid growth of lightning technology, the development of red-emitting phosphors is effective for improving color temperature and color rendering index for w-LEDs devices. Herein, a single phased garnet phosphor with cation and polyhedron substitution modification was firstly prepared. For Mg3Gd2Ge3O12: Bi3+, Eu3+, the intensity has been remarkably improved by about 16% compared to the one without Bi3+ sensitization. The energy transfer mechanism is identified in this work. Based on cation and polyhedron substitution strategies, novel phosphors with different compositions were obtained and further modified the PL properties. With Lu3+ substitution, the bond lengths between Bi3+ ion and anion ligands are decreased and the site symmetry has been strengthened, which leads to a 21 nm blue shift when Lu3+ totally replaced Gd3+ ions. In addition, Lu3+ and [SiO4] substitution strategies both effectively increased symmetric rigid structure, which leads to a significant improvement in thermal stability, indicating the samples own great potential in optical applications This work provides a new insight to synthesis red-emitting phosphors for warm white-LEDs. 相似文献
2.
To investigate the evolution of the structural and enhanced magnetic properties of GdMnO3 systems induced by the substitution of Mn with Cr, polycrystalline GdMn1-xCrxO3 samples were synthesized via solid-state reactions. XRD characterization shows that all GdMn1-xCrxO3 compounds with single-phase structures crystallize well and that Cr3+ ions entering the lattice sites of GdMnO3 induce structural distortion. SEM results indicate that the grain size of the synthesized samples (a few microns) decreases as the Cr substitution concentration increases. Positron annihilation lifetime spectroscopy reveals that vacancy-type defects occur in GdMn1-xCrxO3 ceramics and that the vacancy size and concentration clearly change with the Cr content. The temperature and field dependence of the magnetization curves show that Cr substitution significantly influences the magnetic ordering of the gadolinium sublattice, improving the weak ferromagnetic transition temperature and magnetization of GdMn1-xCrxO3. The enhanced magnetization of GdMn1-xCrxO3 is closely related to the vacancy defect concentration. 相似文献
3.
Su-Il Ri Song-Il Hong Jong-Chol Kim Ju-Hyok Wi 《International Journal of Hydrogen Energy》2021,46(5):3319-3328
We investigated some properties of the hydride Mg2FeH6 substituted with yttrium by a first principles calculation. Some experimental results showed that 4d transition metal, yttrium serves as a good catalyst for magnesium based hydrogen storage alloys, but there are a few theoretical studies about magnesium based hydrides substituted with it. Mg2FeH6 is regarded as a cheaper material than pure MgH2, while it is crystalized into Fm3m structure (space group 225). Although it has high hydrogen storage capacity, many investigations have not been devoted to it due to its extremely high thermodynamic stability. The yttrium substituted Mg2FeH6 exhibits very low energy of formation, and its desorption temperature, 75 °C is very suitable for practical hydrogen storage applications. Our results showed that Mg2FeH6 is destabilized effectively by yttrium substitution and introducing vacancy defects has additive effect to the improvement of dehydrogenation performance. 相似文献
4.
AbstractBa0.95Ca0.05Ti1-xZrxO3 (BCTZO) ceramics were prepared by a solid state reaction method. The samples were characterized by X-ray diffraction (XRD), Scanning electron microscopy (SEM) and X-ray absorption near edge structure (XANES). The ceramics exhibit a pure perovskite structure. The average grain size gradually decreases with increasing Zr concentration. XANES results indicate that the intensities of pre-edge peaks dropped with increasing Zr concentration. The BCTZO ceramic of x?=?0.05 has the optimum electrical properties with the maximum dielectric constant (ε'm), remanent polarization (2Pr), coercive electric field (2Ec) and piezoelectric charge constant (d33) of 7,244, 12.54 (μC/cm2), 5.29 (kV/cm) and 288 (pC/N), respectively. 相似文献
5.
To improve the electrochemical properties of rare-earth–Mg–Ni-based hydrogen storage alloys, the effects of stoichiometry and Cu-substitution on the phase structure and thermodynamic properties of the ... 相似文献
6.
Wenyun Yang Qiwei Hu Guanyi Qiao Liang Zha Shunquan Liu Jingzhi Han Honglin Du Yan Zhang Yingchang Yang Changsheng Wang 《中国稀土学报(英文版)》2019,37(10):1102-1107
In this work, we report the tuning effect of the Si substitution on the magnetic and high frequency electromagnetic properties of R2Fe17 compounds and their paraffin composites. It is found that the introduction of Si can remarkably improve the magnetic and electromagnetic properties of the R2Fe17 compounds, making the R2Fe17–xSix-paraffin composites excellent microwave absorption materials (MAMs). By introducing the Si element, their saturation magnetizations decrease slightly, while much higher Curie temperatures are obtained. Furthermore, better impedance match is reached due to the decrease of the high-frequency permittivity ε′ by about 40%–50%, which finally enhances the performance of the microwave absorption. The peak frequency (fRL) of the reflection loss (RL) curve moves toward high frequency domain and the qualified bandwidth (QB, RL ≤ ?10 dB) increases remarkably. The maximum QB of 3.3 GHz (12.0–15.3 GHz) is obtained for the Sm1.5Y0.5Fe15Si2-paraffin composite (d = 1.0 mm) and the maximum RL of ?53.6 dB is achieved for Nd2Fe15Si2-paraffin composite (d = 2.2 mm), both surpassing most of the reported MAMs. Additionally, a distinguished dielectric microwave absorption peak is observed, which further increases the QB in these composites. 相似文献
7.
首先分析了BMP图像文件格式,然后根据传统LSB算法在BMP图像文件中应用,提出一种改进的LSB隐藏算法,提高了伪装图像质量。最后通过仿真验证了该算法的优越性。 相似文献
8.
用溶胶-凝胶技术在Bi(100)衬底上制备了单层和渐变型多层的BaxSr(1-X)TiO3薄膜,其膜层组分分别为:Ba0.7Sr0.3TiO3,Ba0.8Sr0.2TiO,Ba0.9Sr0.1TiO3,BaTiO3,对生长制备出的多层BaxSr(1-X)TiO3薄膜进行了变角度椭偏光谱测量,通过椭偏光谱解谱分析研究,首次得到了BaxSr(1-X)TiO3多层膜结构不同膜层的膜厚和光学常数,其结果显示:椭偏光谱分析得到的不同膜层的膜厚与卢瑟福背向散射测量得到的结果基本相符;渐变型多层膜中BaTiO3薄膜的折射率比单层BaTiO3薄膜折射率大许多,与体BaTiO3的折射率相接近,这说明渐变型多层膜中BaTiO3薄膜的光学性质与体材料的光学性质接近。 相似文献
9.
阳离子化多元醇防塌剂的研制 总被引:4,自引:0,他引:4
室内研究和现场应用表明,聚乙烯醇类防塌剂表现出较明显的增粘负效应,可引起钻井液粘度的急剧增加,严重影响其推广应用.通过金属盐催化降解和阳离子化反应,研制出了抑制性好且增粘负效应低的阳离子化改性多元醇防塌剂.考察了阳离子化试剂、反应温度、反应时间对取代度、反应效率和产品主要性能的影响,得出了阳离子化多元醇防塌剂最佳制备条件,即:PVA与阳离子化试剂物质的量比为1:1,反应温度为50℃,反应时间为4 h,阳离子度可达0.435. 相似文献
10.