共查询到18条相似文献,搜索用时 312 毫秒
1.
采用基于密度泛函理论的第一性原理方法, 在广义梯度近似(GGA)和GGA+U方法下对尖晶石型LiMn2O4及其Al掺杂 的尖晶石型LiAl0.125Mn1.875O4晶体的结构和电子性质进行了计算. 结果表明: 采用GGA方法得到尖晶石型LiMn2O4是立方晶系结构, 其中的Mn离子为+3.5价, 无法解释它的Jahn-Teller 畸变. 给出的LiMn2O4能带结构特征也与实验结果不符. 而采用GGA+U方法得到在低温下的LiMn2O4和其掺杂 体系LiAl0.125Mn1.875O4的晶体都是正交结构, 与实验一致. 也能明确地确定Mn的两种价态Mn3+/Mn4+的分布并且能够说明Mn3+O6的z方向有明显的Jahn-Teller 畸变, 而Mn4+O6则没有畸变. LiMn2O4的能带结构与实验比较也能够符合. 采用GGA+U方法对Al掺杂体系的LiAl0.125Mn1.875O4的研究表明, 用Al替换一个Mn不会明显地改变晶体的电子性质, 但可以有效地消除Al3+O6 八面体的Jahn-Teller畸变, 从而改善正极材料LiMn2O4的性能, 这与电化学实验的观察结果相一致. 相似文献
2.
利用传统的固相反应法制备了BiFe1-xMnxO3 (x= 0-0.20)陶瓷样品, 研究了不同Mn4+掺杂量对BiFeO3陶瓷密度、物相结构、显微形貌、 介电性能和铁电性能的影响.实验结果表明:所制备的BiFe1-xMnxO3 陶瓷样品的钙钛矿主相均已形成,具有良好的晶体结构, 且在掺杂量x=0.05附近开始出现结构相变.随着Mn4+添加量的增加, 体系的相结构有从菱方钙钛矿向斜方转变的趋势,且样品电容率大幅度增大, 而介电损耗也略有增加;在测试频率为104 Hz条件下, BiFe0.85Mn0.15O3 (εr=1065)的 εr是纯BiFeO3 (εr=50.6)的22倍; 掺杂后样品的铁电极化性能均有不同程度的提高,可能是由于Mn4+稳定性优于 Fe3+,高价位Mn4+进行B位替代改性BiFeO3陶瓷, 能减少Bi3+挥发,抑制Fe3+价态波动,从而降低氧空位浓度,减小样品的电导和漏电流. 相似文献
3.
4.
采用共沉淀法制备了纳米晶ZrO2-Al2O3∶Er3+发光粉体.所制备的粉体室温下具有Er3+离子特征荧光发射,主发射在绿光,其中位于547 nm、560 nm的绿光最强,并得出稀土离子与基质之间有能量传递.对不同煅烧温度下的样品研究表明:因不同温度下所制得的样品晶相不同.研究了纳米晶ZrO2-Al2O3∶Er3+及ZrO2-Al2O3∶Er3+/Yb3+的上转换发光,并分析了上转换的跃迁机制.发现ZrO2-Al2O3∶Er3+的绿光为双光子过程,而ZrO2-Al2O3∶Er3+、Yb3+的上转换光谱中,红光和绿光也为双光子过程,而极弱的蓝光为三光子过程.讨论了Er3+的浓度猝灭现象.最适宜掺杂浓度的原子分数为2%(Er3+/Zr4+). 相似文献
5.
6.
以传统的浸渍法,在不同焙烧温度下制备了用于CO氧化反应的Co3O4/SiO2催化剂.通过激光拉曼光谱(Raman)、X射线光电子能谱(XPS)、X射线衍射(XRD)、程序升温还原(TPR)和X射线吸收精细结构谱(XAFS)表征了该系列催化剂的结构.在所有的催化剂中,XRD和Raman光谱都只检测到了Co3O4晶相的存在.与Co3O4体相相比,XPS结果表明在200 oC焙烧的(Co3O4(200)/SiO2)催化剂中Co3O4表面上存在着过量的Co2+.与XPS的结果一致,TPR结果表明Co3O4(200)/SiO2催化剂中Co3O4表面上存在氧缺陷, 并且XAFS结果也表明Co3O4(200)/SiO2催化剂中Co3O4具有更多的Co2+.提高焙烧温度使得过量的Co2+进一步氧化为Co3+,同时降低了表面氧缺陷浓度,从而得到计量比的Co3O44/SiO2催化剂.在所有的负载催化剂中Co3O4(200)/SiO2催化剂表现出了最好的CO氧化催化性能,表明过量Co2+和表面氧缺陷的存在能够促进Co3O4催化CO氧化反应的活性. 相似文献
7.
本文制备了用于费托合成反应的钴改性Fe3O4-MnO2双功能催化剂,并探究了钴负载量对Fe-Co协同效应的影响以及Fe1CoxMn1催化剂的费托合成反应性能. 实验发现,在Fe3O4-Mn催化剂中加入Co可促进铁氧化物的还原、增加反应过程中铁位点的活性. 此外,Co的加入可增强Fe-Co金属间的电子转移,加强两者的协同作用,提高催化性能. Co负载较高的Fe1CoxMn1催化剂可进一步促进加氢反应能力,使产品分布向短链烃方向转移. 在280 °C、2.0 MPa和3000 h-1的最佳工况条件下,Fe1Co1Mn1催化剂的液体燃料收率最高. 相似文献
8.
通过在碱液中共沉淀Mn2+、Ni2+和Fe2+后制备了棒状的前躯体,前躯体于不同温度煅烧后制得了MnxNi0:5-xZn0:5Fe2O4棒状体. 利用X射线衍射仪和透射电镜对棒状体的物相、形貌及粒径进行了表征,并利用振动样品磁强计对磁性能进行研究. 结果表明长径比大于15的棒状,随着x值的增加,MnxNi0:5-xZn0:5Fe2O4样品的直径增加,长度下降,长径比变小,当x=0.5时其直径在50 nm左右而长径比减小到7~8. 随着x值的增加,样品的矫顽力先增加后减少,x值达到0.4时样品的矫顽力再次增加,当煅烧温度为600 oC,x=0.5时样品的矫顽力最大为134.3 Oe. 饱和磁化强度随着x值的增加先增加后减少,当煅烧温度为800 oC和x=0.2时达到最大为68.5 Oe. 相似文献
9.
10.
采用传统固相法和水热法成功地制备出棒状La2Zr2O7:Eu3+荧光粉. 利用X射线粉末衍射仪、透射电镜和荧光光谱仪等分析了产物的结构、形貌和发光特性. 结果表明红色荧光粉La2Zr2O7:Eu3+有良好的晶相,属于立方结构,空间点群为Fd3m; 其形貌主要为纳米棒, 平均直径约47 nm, 长度为50~700 nm. 并对纳米棒的生长机理进行了探讨. 在466 nm蓝光激发下,La2Zr2O7:Eu3+荧光粉能发射出Eu3+的特征红色荧光,发射主峰位于616 nm处,归属于Eu3+的5DO→7F2超灵敏电偶极跃迁.此外,在产物的发射光谱中能够观察到5D1→7FJ (J=0, 1, 2)跃迁和5D1→7FJ (J=1, 2, 4)跃迁的劈裂峰,这说明Eu3+处在低对称性的晶体场格位中. 相似文献
11.
Monodisperse Au-Fe 3 O 4 heterodimeric nanoparticles (NPs) were prepared by injecting precursors into a hot reaction solution.The size of Au and Fe 3 O 4 particles can be controlled by changing the injection temperature.UV-Vis spectra show that the surface plasma resonance band of Au-Fe 3 O 4 heterodimeric NPs was evidently red-shifted compared with the resonance band of Au NPs of similar size.The as-prepared heterodimeric Au-Fe 3 O 4 NPs exhibited superparamagnetic properties at room temperature.The Ag-Fe 3 O 4 heterodimeric NPs were also prepared by this synthetic method simply using AgNO 3 as precursor instead of HAuCl 4.It is indicated that the reported method can be readily extended to the synthesis of other noble metal conjugated heterodimeric NPs. 相似文献
12.
13.
Fe3O4-based heterostructures, including Fe3O4/MgO/Fe3O4, Fe3O4/MgO/Si and Fe3O4/SiO2/Si, were fabricated by magnetron sputtering to investigate the perpendicular-to-plane magneto-transport properties. In the Fe3O4/MgO/Fe3O4 and Fe3O4/MgO/Si heterostructures, the typical magneto-transport properties of single Fe3O4 films, such as negative magnetoresistance (MR) and extreme values of MR−T curves at 120 K, were observed, suggesting that the spin polarization of conducting electrons conserves through MgO barrier. MR in the Fe3O4/MgO/Fe3O4 heterostructure is larger than that in the Fe3O4/MgO/Si heterostructure, because the spin of electrons is disturbed in the depletion layer of Si and the SiO2 layer introduced by Fe3O4/MgO growth. The Fe3O4/SiO2/Si heterostructure has a positive MR of 2% at 120 K, which may originate from the scattering of conducting electrons in amorphous SiO2 and the spin polarization reversal at the Fe3O4/SiO2 interface. 相似文献
14.
Facile Synthesis of Gd(OH)3‐Doped Fe3O4 Nanoparticles for Dual‐Mode T1‐ and T2‐Weighted Magnetic Resonance Imaging Applications 下载免费PDF全文
Hongdong Cai Xiao An Shihui Wen Jingchao Li Guixiang Zhang Xiangyang Shi Mingwu Shen 《Particle & Particle Systems Characterization》2015,32(10):934-943
The facile hydrothermal synthesis of polyethyleneimine (PEI)‐coated iron oxide (Fe3O4) nanoparticles (NPs) doped with Gd(OH)3 (Fe3O4‐Gd(OH)3‐PEI NPs) for dual mode T1‐ and T2‐weighted magnetic resonance (MR) imaging applications is reported. In this approach, Fe3O4‐Gd(OH)3‐PEI NPs are synthesized via a hydrothermal method in the presence of branched PEI and Gd(III) ions. The PEI coating onto the particle surfaces enables further modification of poly(ethylene glycol) (PEG) in order to render the particles with good water dispersibility and improved biocompatibility. The formed Fe3O4‐Gd(OH)3‐PEI‐PEG NPs have a Gd/Fe molar ratio of 0.25:1 and a mean particle size of 14.4 nm and display a relatively high r2 (151.37 × 10?3m ?1 s?1) and r1 (5.63 × 10?3m ?1 s?1) relaxivity, affording their uses as a unique contrast agent for T1‐ and T2‐weighted MR imaging of rat livers after mesenteric vein injection of the particles and the mouse liver after intravenous injection of the particles, respectively. The developed Fe3O4‐Gd(OH)3‐PEI‐PEG NPs may hold great promise to be used as a contrast agent for dual mode T1‐ and T2‐weighted self‐confirmation MR imaging of different biological systems. 相似文献
15.
利用Sol-Gel法在Pt/Ti/SiO2/Si衬底上制备出Bi4Ti3O12和Bi3.25La0.75Ti3O12薄膜,研究了La掺杂对Bi4Ti3O12薄膜的晶体结构、铁电性能和疲劳特性的影响,发现La掺杂没有改变Bi4Ti3O12薄膜的基本晶体结构,并且提高了Bi4Ti3O12铁电薄膜的剩余极化值和抗疲劳性能,对La掺杂改善Bi4Ti3O12铁电薄膜性能的机理进行了讨论.
关键词:
铁电性能
4Ti3O12薄膜')" href="#">Bi4Ti3O12薄膜
3.25La0.75Ti3O12薄膜')" href="#">Bi3.25La0.75Ti3O12薄膜
sol-gel法
La掺杂 相似文献
16.
通过固相反应法制备了Er3+/Yb3+共掺杂ZrO2-Al2O3粉末的样品,并对样品在980nm激光激发下的上转换发光特性进行了研究.从发射光谱可以发现,在可见光范围内有3个强的发光带,一个位于654nm附近的红光带和两个分别位于545nm、525nm附近的绿光带,分别对应于Er3+离子的以下辐射跃迁:4F9/2→4I15/2、4S3/2→4I15/2、 2H11/2→4I15/2.其中又以Er3+离子的4F9/2→4I15/2跃迁产生的红色荧光辐射最强.对其上转换发光机制进行了分析,发现这三个发光过程都是双光子过程.对样品粉末进行了XRD检测,发现ZrO2主要以立方相为主,并且计算得到了这种立方结构的晶格常数.Al2O3固溶于ZrO2中,Al3+嵌入ZrO2后产生氧空位,导致ZrO2晶体的对称性降低,这种结构变化更有利于提高上转换效率,即上转换发光强度增强.
关键词:
3+/Yb3+')" href="#">Er3+/Yb3+
上转换
2-Al2O3')" href="#">ZrO2-Al2O3
荧光
稀土 相似文献
17.
R. Kita N. Hosoya N. Otawa S. Kawabata T. Nakamura O. Miura M. Mukaida K. Yamada A. Ichinose K. Matsumoto M.S. Horii Y. Yoshida 《Physica C: Superconductivity and its Applications》2009,469(15-20):1157-1160
We investigated the effects of added Tm2O3, Sc2O3, and Yb2O3 on the superconducting properties of sintered Er123 samples. Tm2O3 addition caused the least Tc degradation, exhibiting a Tc above 90 K even for 17 vol% addition. Samples with added Sc2O3 maintained a Tc at above 90 K up to an addition of 7.2 vol%, while Yb2O3-containing samples showed a monotonic decrease in Tc with increased vol% of added Yb2O3. Tm2O3-containing samples exhibited a slight increase in Jc(0.1 T)/Jc(0) and had constant Jc values even for 17 vol% addition. XRD and SEM results indicate that the Tm2O3 is very stable in the superconducting matrix. 相似文献
18.
K.D OskamK.A Kaspers A Meijerink H Müller-BunzTh Schleid 《Journal of luminescence》2002,99(2):101-105
The luminescence properties of Ce3+ in La3F3[Si3O9] are reported. Excitation and emission bands corresponding to 4f1→5d1 transitions of Ce3+ were identified. The center of gravity of the 5d states lies at remarkable high energy (43.2×103 cm−1) for Ce3+ in a silicate compound. This high value is attributed to the combined oxygen/fluoride coordination of the Ce3+ ion. Emission from the lowest 4f5d level to the 2F5/2 and 2F7/2 levels was found at 32.4×103 and 30.4×103 cm−1. These results are compared with literature data on silicates and fluorides. From the values found for Ce3+, predictions are made for the positions of the 4f5d bands of Pr3+ and Er3+ in La3F3[Si3O9]. For both ions, it is concluded that in this host lattice emission is expected from high lying 4fn energy levels. 相似文献