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1.
The effect of cobalt-doping on the magnetic, transport and magnetoresistance characteristics of La1-xSrxMnO3 was investigated. The results show that the magnetoelectric property of
rare-earth doped manganites is greatly affected by substitution of Co for Mn sites. The Curie temperature as well as the magnetic moment decreases with the increase of doping concentration, and the samples exhibit obvious characteristics of the spin glass state. Moreover, the magnetoresistance is evidently modulated by doping concentration,
and the relevant temperature dependence is also suppressed. In addition, low-temperature magnetoresistance is significantly
promoted as doping concentration increases, which renders a value of approximately 50% in the temperature range of 5--200~K and varies within 12.5%. It can be attributed to the effect of spin scattering, induced by cobalt doping, on the itinerant electrons of Mn ions, thus introducing a spin-disorder region into the ferromagnetic region of double-exchange interaction between neighbouring Mn3+ and Mn 3+ ions. 相似文献
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3.
The structural and electronic transport properties of La1−x
Ce
x
MnO3 (x=0.0–1.0) have been studied. All the samples exhibit orthorhombic crystal symmetry and the unit cell volume decreases with
Ce doping. They also make a metal-insulator transition (MIT) and transition temperature increases with increase in Ce concentration
up to 50% doping. The system La0.5Ce0.5MnO3 also exhibits MIT instead of charge-ordered state as observed in the hole doped systems of the same composition. 相似文献
4.
采用柠檬酸溶胶凝胶结合陶瓷烧结工艺制备了Ca位置换Fe的Ca1-xFexMnO3(x=0-0.12)氧化物粉末及块体试样,通过X射线衍射及电参数测试分析了所得试样.实验结果表明:在实验范围内,所有试样呈单一物相,Ca位置换Fe之后随置换量的增加,CaMnO3的晶胞逐渐变小,晶粒长大受到抑制.测试温度范围内所有试样均呈半导体输运特性,电输运机制未发生变化;当x在0-
关键词:
3')" href="#">CaMnO3
Fe置换
电输运 相似文献
5.
P掺杂对绿色荧光粉BaMgAl$lt;sub$gt;10$lt;/sub$gt;O$lt;sub$gt;17$lt;/sub$gt;:Mn$lt;sup$gt;2+$lt;/sup$gt;性能的影响 下载免费PDF全文
采用高温固相法合成P掺杂的BaMgAl10O17:Mn2+荧光粉,其中P通过(NH4)2HPO4引入.利用X射线衍射谱、傅里叶变换红外光谱、扫描电子显微镜、能量色散谱、真空紫外光谱等研究了P掺杂对BaMgAl10O17:Mn2+晶体结构、微观形貌、发光性能等的影响.研究结果表明:(NH4)2HPO4具有助熔剂的作用,它的加入有助于荧光粉的晶化,改善荧光粉的形貌.P掺杂进入晶格,使得晶胞参数变小,从而改变了Mn2+的晶体场环境,引起发射光谱蓝移,色坐标x值降低.P掺杂能有效提高基质对真空紫外线的吸收,从而提高真空紫外激发下的发光强度.
关键词:
P掺杂
10O17:Mn2+')" href="#">BaMgAl10O17:Mn2+
晶体结构
真空紫外 相似文献
6.
Electronic and optical properties of pure and Mo doped anatase TiO2 using GGA and GGA+U calculations
Comparative GGA and GGA+U calculations for pure and Mo doped anatase TiO2 are performed based on first principle theory, whose results show that GGA+U calculation provide more reliable results as compared to the experimental findings. The direct band gap nature of the anatase TiO2 is confirmed, both by using GGA and GGA+U calculations. Mo doping in anatase TiO2 narrows the band gap of TiO2 by introducing Mo 4d states below the conduction band minimum. Significant reduction of the band gap of anatase TiO2 is found with increasing Mo doping concentration due to the introduction of widely distributed Mo 4d states below the conduction band minimum. The increase in the width of the conduction band with increasing doping concentration shows enhancement in the conductivity which may be helpful in increasing electron–hole pairs separation and consequently decreases the carrier recombination. The Mo doped anatase TiO2 exhibits the n-type characteristic due to the shifting of Fermi level from the top of the valence band to the bottom of the conduction band. Furthermore, a shift in the absorption edge towards visible light region is apparent from the absorption spectrum which will enhance its photocatalytic activity. All the doped models have depicted visible light absorption and the absorption peaks shift towards higher energies in the visible region with increasing doping concentration. Our results describe the way to tailor the band gap of anatase TiO2 by changing Mo doping concentration. The Mo doped anatase TiO2 will be a very useful photocatalyst with enhanced visible light photocatalytic activity. 相似文献
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采用密度泛函理论中广义梯度近似对非典型富勒烯C22和过渡金属内掺衍生物M@C22(M=Sc,Ti,V,Cr,Mn,Fe,Co和Ni)的几何结构和电子结构进行计算研究.发现非典型富勒烯C22的基态结构是含有一个四碳环的单重态笼状结构.过渡金属原子的掺入明显提高了体系的稳定性. C-M键既有一定共价性又有一定离子性.磁性、能级图、轨道分布和态密度图分析表明: M原子的3d轨道和碳笼的C原子的原子轨道之间存在较强的轨道杂化. Ti, Cr, Fe和Ni内掺的结构出现磁性完全猝灭现象. Sc和碳笼间是弱反铁磁作用, V,Mn和Co与碳笼间是弱铁磁作用. 相似文献
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10.
ABSTRACTThe blue phase of YBa2Cu3O7- δ (YBCO) family, Y2Cu2O5 (Y202) nanoparticles were prepared and doped into (YBCO) superconductor and the effect of doping on critical current density and critical temperature was investigated. Y202 nanoparticles with particle sizes of 47, 107 and 206?nm were prepared by a sol–gel combustion method and added into the YBCO superconductor by 0.5–2?wt.%. XRD and scanning electron microscope measurements were used to characterize the samples. The measurement of critical current density at 77?K revealed that the doped superconductors had larger critical current density compared to the undoped superconductors. For a fixed dopant concentration, by increasing the size of nanoparticles, the Jc was increased. For the samples including 0.5?wt.% of nanoadditives, Jc was higher. The highest critical current density of 137?A/cm2 was measured for the superconductors containing 0.5?wt.% of 206?nm Y202 nanoparticles. Also, by increasing the nanoparticles concentration, the Tc was reduced. 相似文献
11.
采用基于密度泛函理论(DFT)的第一性原理赝势平面波方法, 通过自旋极化的广义梯度近似(GGA)电子结构计算对梯形化合物NaV2O4F进行了研究. 考虑了四种假想的自旋有序态,计算结果表明该化合物的磁基态具有二维反铁磁(AFM)结构, 即沿梯阶和梯腿方向都表现为AFM作用. 能带结构显示NaV2O4F为绝缘体材料, 带隙约为1.0eV. 方锥体中的晶体场劈裂使得VO4F方锥体中的 V4+
关键词:
2O4F')" href="#">NaV2O4F
梯形化合物
第一性原理计算
电子结构 相似文献
12.
The spin Hamiltonian parameters (SHPs) and the local structures for impurity W5+ in the Zn3(PO4)2ZnO nanopowders doped with WO3 under different concentrations are theoretically investigated using the perturbation calculations of these parameters. The exponential functions of the related quantities (cubic field parameter Dq, covalency factor N, relative tetragonal compression ratio τ and core polarisation constant κ) of concentration x with totally four adjustable coefficients a, b, c and d are adopted to fit the concentration dependences of the experimental d-d transition bands and SHPs. The impurity W5+ centres demonstrate moderate tetragonal compression ratios τ (~3.1%) due to the Jahn–Teller effect. With the increase of WO3 concentration, Dq and N show moderately decreasing rules, while τ and κ exhibit slightly and moderately increasing tendencies with x, respectively. The mechanisms of the above concentration dependences of these quantities are analysed from the modifications of the local crystal-field strength and electron cloud density around the impurity W5+ with the variation of x. Present theoretical studies would be useful to the exploration of the structural properties and optical applications for WO3 doped Zn3(PO4)2ZnO nanopowders. 相似文献
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The electronic structures of doped Sb2O5 by IV-family elements (Si, Ge and Sn) were examined using the density function theory (DFT). Density of states (DOSs) results
showed that the substituted IV-family elements act as acceptors in Sb2O5. Partial DOSs indicates that by substituting Ge(Ge
Sb
) or Sn(Sn
Sb
), there may be a larger contribution to the total DOSs near E
F
than by substituting Si, which suggests that doping Ge or Sn in Sb2O5 produces better ptype doping compared to doping Si. Formation energy results show that IV-family elements are more likely
to exist in the substituted position rather than in the interstitial position in Sb2O5, decreasing any self-compensation effect and making it easier for IV-family elements to realize ptype doping in Sb2O5. Ionization energy results show that Ge
Sb
or SnSb, two among the three impurities considered, act as shallow acceptors in Sb2O5, thus producing a higher concentration of holes.
相似文献
15.
H.H. Wen G. Mu X.Y. Zhu P. Cheng L. Fang F. Han B. Zeng B. Shen 《Physica C: Superconductivity and its Applications》2009,469(15-20):894-897
Bulk superconductivity was observed in the FeAs-based RE1−xSrxFeAsO (RE = La, Pr) when the di-valence element Sr was substituted to the site of the tri-valence element La and Pr. The maximum superconducting transition temperatures Tc for the two systems are 26 K and 16.3 K, respectively. The doping dependence of the electrical properties and structure of these two systems were investigated systematically. A roughly monotonic increase of Tc and the lattice constants (a-axis and c-axis) with Sr concentration and a saturation behavior in the high doping levels were found. We confirmed that conduction in this type of materials is dominated by hole-like charge carriers by the Hall effect measurements. Also the resistive measurements revealed possible higher upper critical field in these systems comparing with the electron-doped ones. 相似文献
16.
使用基于密度泛函理论的CASTEP软件计算了BAM:Eu2+(BaMgAl10O17:Eu2+)荧光粉在SiN掺杂前后的能带、态密度、吸收光谱和Mulliken布居.Eu2+处于BR位置光吸收更强;SiN掺杂使处于BR位置的Eu2+的数量上升,而处于mO位置的Eu2+的数量下降,抵消了SiN掺杂降低Eu的态密度对光谱的影响.所以适量掺杂的SiN提高了BAM:Eu2+荧光粉的吸收发射光谱强度.Si-N键和Eu-N键的Mulliken布居数分别高于Al-O键和Eu-O键, 说明Si-N键和Eu-N键的共价性分别强于Al-O键和Eu-O键.发光中心Eu2+局域结构共价性的增强降低了BAM:Eu2+镜面层的活性,这是SiN掺杂提高BAM:Eu2++荧光粉光学稳定性的主要原因. 相似文献
17.
采用了传统的固相烧结工艺,制备了不同Zr和Hf掺杂量的SrBi4Ti4-xZrxO15(x=000,003, 006,010,020)和SrBi4Ti4-xHfxO15(x=000,0005, 0015,0030,0060)的陶瓷
关键词:
4Ti4-xZrxO15')" href="#">SrBi4Ti4-xZrxO15
4Ti4-xHfxO15')" href="#">SrBi4Ti4-xHfxO15
铁电性能
介电性能 相似文献
18.
成功生长了Co50Ni21Ga29:Si(x=1,2)单晶样品,对其磁性,马氏体相变及其相关性质进行了细致的测量.发现掺Si成分的单晶具有非常迅速的马氏体相变行为、2.5%的大相变应变、大于100 ppm的磁感生应变和4.5%的相变电阻.进一步研究指出,在CoNiGa合金中掺入适量Si元素,能够降低材料的马氏体相变温度,减小相变热滞后,提高材料的居里温度,并使得磁性原子的磁矩有所降低.尤其重要的是Si元素的添加能够增大材料马氏体的磁晶各向异性能,改善马氏体变体的迁移特性,从而获得更大的磁感生应变.
关键词:
铁磁形状记忆合金
Heusler合金
50Ni21Ga29Six')" href="#">Co50Ni21Ga29Six 相似文献
19.
20.
Y. Zhang C.H. Cheng Y.L. Chen Y.J. Cui W.G. You H. Zhang Y. Zhao 《Physica C: Superconductivity and its Applications》2010,470(20):1073-1076
The electronic structures of Fe-based superconductor SmFeAsO1−xFx and SmFe1−yIryAsO are compared through X-ray photoemission spectroscopy in this study. With fluorine or iridium doping, the electronic structure and chemical environment of the SmFeAsO system were changed. The fluorine was doped at an oxygen site which introduced electrons to a reservoir Sm–O layer. The iridium was doped at an Fe site which introduced electrons to a conduction Fe–As layer directly. In a parent material SmFeAsO, the magnetic ordering corresponding to Fe3d in the low-spin state is suppressed by both fluorine and iridium doping through suppressing the magnetism of 3d itinerant electrons. Compared to fluorine doping, iridium doping affected superconductivity more significantly due to an iridium-induced disorder in FeAs layers. 相似文献