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1.
Phase evolution in the Bi---Sr---Ca---Cu---Al---O system was studied. Two Al-containing phases BiSr1.5Ca0.5Al2Oz and (Sr1−xCax)3Al2O6 (x = 0.4 − 0.45) were determined to be chemically compatible with Bi2.18Sr2CaCu2O8+x (Bi-2212) at temperatures of the samples processing. The phase equilibria in the title system were investigated above the solidus temperature. The BiSr1.5Ca0.5Al2Oz was found to be in equilibrium only with the melt and the (Sr1−xCax)3Al2O6 phase. This latter aluminate equilibrated with Ca,Sr cuprates, CaO, the Cu-free phase, and the liquid. The melting and solidification in Bi-2212, doped with the aluminate, corresponded to the reversible reaction Bi-2212 + BiSr1.5Ca0.5Al2Oz ↔ (Sr1−xCax)3Al2O6 + liquid. Two sets of superconducting composite materials with initial compositions Bi-2212 + nBiSr1.5Ca0.5Al2Oz and Bi-2212 + m(Sr1−xCax)3Al2O6 were prepared by solidification from the partial melt. The former material was composed mostly of large Bi-2212 lamellas separated by the BiSr1.5Ca0.5Al2Oz phase, which destroyed superconducting links between Bi-2212 grains. The latter material consisted of a Bi-2212 polycrystalline matrix with high concentration of small (ca. 3 μm) grains of (Sr1−xCax)3Al2O6 imbedded in Bi-2212 lamellas. The Bi-2212 + m(Sr1−xCax)3Al2O6 materials displayed a trend to enhance flux pinning at T = 60 K with the increase of aluminate phase content.  相似文献   

2.
The crystal structures of (Pb0.5Cd0.5)Sr2YCu2O7, (Pb0.5Cd0.5)Sr2(Y0.6Ca0.4)Cu2O7 and (Pb0.5Cd 0.5)Sr2(Y0.5Ca0.5)Cu2O7 have been refined by the Rietveld method for the X-ray diffraction data. The refinement results indicate that both Pb and Cd atoms in the (Pb, Cd)O layers and O(3) atoms are displaced from their ideal sites, and that there is a complicated occupation in the (Pb, Cd)O layers, i.e., other cations, such as Sr2+, Cu2+ and Ca2+, can occupy the (Pb, Cd) site for these samples. This may be the reason why the lattice constants do not vary monotanically with the calcium content, and why there exist broad superconducting transitions in the system (Pb0.5Cd0.5)Sr2(Y1−xCax)Cu2O7. The refinement results also indicate that, as the calcium content increases, the O(2) atoms move close to the CuO2 planes and far from the (Pb, Cd)O layers. Thus, the increase of calcium content results in charge transfer from the charge reservoir layer (Pb, Cd)O to the CuO2 planes. This result is consistent with the bond valence sums of the Cu ions in the CuO2 planes.  相似文献   

3.
A series of rare-earth (RE)-doped nanocrystalline CoFeMn0.9RE0.1O4 thin films were prepared on monocrystalline silicon substrate by a sol–gel process, and the influences of the various RE3+ ions on the microstructure, magnetism and polar magneto-optical Kerr effects of the as-deposited films were examined. The results revealed that both of the magnetism and Kerr effect of CoFeMn0.9RE0.1O4 films could be mediated by doping with various RE3+ ions. The trend of both MS and HC of CoFeMn0.9RE0.1O4 films is similar to that of Bohr magneton across the series of rare-earth ions. The position of Kerr rotation peaks was red-shifted and their intensities increased, especially when doping with La3+, Tb3+, Y3+ or Yb3+ and so on. The enhanced MOKEs in CoFeMn0.9RE0.1O4 nanocrystalline thin films might promise their applications for magneto-optical recording in the future.  相似文献   

4.
黄禹田  王煜  朱敏敏  吕婷  杨洪春  李翔  王秀章  刘美风  李少珍 《物理学报》2018,67(15):154203-154203
为了寻求新的非常规多铁性材料,采用固相合成方法制备具有Ruddlesden-Popper结构的(1-x)Sr_3Sn_2O_7+x Ca_3Mn_2O_7(SSO+CMO)(x=0,0.05,0.10,0.15,0.20)系列陶瓷.通过X射线衍射、紫外可见光谱和磁性测量,发现SSO+CMO陶瓷为单一正交相结构,空间群为A21am.随着掺杂量x的增加,样品的晶胞参数和体积相应地减小;在室温不同频率下,样品的介电常数和介电损耗随着频率增加而减小,且在x=0.1时有弱的铁磁性.  相似文献   

5.
We report normal-state and superconducting properties of the clathrate-type silver-oxide Ag6O8AgHF2. We present electrical resistivity, DC- and AC-susceptibility and specific-heat measurements of single crystalline Ag6O8AgHF2. In the normal state, Ag6O8AgHF2 exhibits metallic conductivity and a phase transition near 110 K, possibly a structural phase transition as observed in the related compound Ag6O8AgNO3. The onset of superconductivity of our samples is observed around 1.2–1.5 K, and the HT phase diagram is determined for the first time. The upper critical field Hc2(0) is estimated to be about 2000–2200 Oe and the coherence length ξGL(0) to be 40 nm.  相似文献   

6.
Sol–gel derived Fe2O3 films containing about 10 wt% of Er2O3 were deposited on porous silicon by dipping or by a spin-on technique followed by thermal processing at 1073 K for 15 min. The samples were characterized by means of PL, SEM and X-ray diffraction analyses. They exhibit strong room-temperature luminescence at 1.5 μm related to erbium in the sol–gel derived host. The luminescence intensity increases by a factor of 1000 when the samples are cooled from 300 to 4.2 K. After complete removal of the erbium-doped film by etching and partial etching the porous silicon, the erbium-related luminescence disappears. Following this, luminescence at 1.5 μm originating from optically active dislocations (“D-lines”) in porous silicon was detected. The influence of the conditions of synthesis on luminescence at 1.5 μm is discussed.  相似文献   

7.
Polarized micro-Raman spectra of different compounds belonging to the Sr14Cu24O41-type structure were studied. In the spectra with parallel polarization along the plane crystal axes of the insulating samples Sr9R5Cu24O41 (R = La, Y) a broad peak near 3000 cm−1, similar to the well-known two-magnon peak in the layered cuprates, was observed. In addition to the Raman lines characteristic for this structure, we observed only in the spectra with parallel to the chains numerous lines between 100 and 1200 cm−1, probably originating from Raman-forbidden infrared-active only LO phonons and their combinations. In the spectra of the conducting compounds Sr14−xCaxCu24O41 (x = 0,7) these features were very weak or disappeared. We interpret these results as Raman evidence for hole doping of the Cu2O3 “spin-ladder” planes and for a redistribution of holes between chains and planes through Ca substitution in the case of the rare-earth-free samples.  相似文献   

8.
c-Axis oriented GaN nanocrystalline thin films were fabricated by nitridation of three different thin films of -GaO(OH), -Ga2O3 or β-Ga2O3 obtained by sol–gel technique on amorphous quartz glass substrates. All these GaN thin films showed near band edge emission at 390 nm and yellow luminescence at 570 nm. The crystalline nature and c-axis orientation as well as luminescence properties of the GaN thin films increased by several times by using a buffer layer of GaN on the substrate.  相似文献   

9.
LiMn2O4 thin films were prepared by a sol–gel method using spin-coating and annealing processes. Anhydrous Mn(CH3COCHCOCH3)3 (manganese acetylacetonate) and LiCH3COCHCO–CH3 (lithium acetylacetonate) were chosen as source materials. The film electrochemical properties depended on the drying temperature even when subjected to the same annealing conditions. The discharge capacity of annealed film increased as the drying temperature was increased. However, the rate of capacity fading during cycling increased as the drying temperature was increased.  相似文献   

10.
The paper represents a detailed insight into the correlation between changes of the phase composition of crystalline YbxZr1−xO2−x/2 solid solutions and their structural, electrical, mechanical and optical properties. Particularly, the effect of the crystal growth conditions and stabilizer amount in the range of 1.5–13.8 mol% of Yb2O3 are studied in terms of Rietveld analysis of powder X-ray diffraction data, electrical conductivity measured by impedance spectroscopy, absorption coefficient and refractive index measurements, Vickers microhardness (classical technique) as well as the plastic microhardness and effective elastic modulus (DSI—depth-sensing indentation technique). Potential applications of the investigated systems are discussed in view of the results obtained.  相似文献   

11.
采用高温固相法在800℃下制备出系列白色长余辉荧光粉Sr3Al2O5Cl2:Eu2+,Tm3+,并研究了它们的结构、形貌及发光性能。样品Sr2.91Al2O5Cl2:0.04Eu2+,0.05 Tm3+具有单一晶相和纳米纤维结构。该样品在紫外光激发下表现出两个很强的宽带发射(分别位于~448 nm和~590 nm)。它的余辉寿命大约是20 min。利用此种荧光粉所制作出的白光LED器件表现出很强的白光发射。  相似文献   

12.
Pure and rare earth doped gadolinium oxide (Gd2O3) waveguide films were prepared by a simple sol–gel process and dip-coating method. Gd2O3 was successfully synthesized by hydrolysis of gadolinium acetate. Thermogravimetric analysis (TGA) and differential thermal analysis (DTA) were used to study the thermal chemistry properties of dried gel. Structure of Gd2O3 films annealed at different temperature ranging from 400 to 750 °C were investigated by Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD) and transmission electron microscopy (TEM). The results show that Gd2O3 starts crystallizing at about 400 °C and the crystallite size increases with annealing temperature. Oriented growth of (4 0 0) face of Gd2O3 has been observed when the films were deposited on (1 0 0) Si substrate and annealed at 750 °C. The laser beam (λ=632.8 nm) was coupled into the film by a prism coupler and propagation loss of the film measured by scattering-detection method is about 2 dB/cm. Luminescence properties of europium ions doped films were measured and are discussed.  相似文献   

13.
费潇  罗炳成  金克新  陈长乐 《物理学报》2015,64(20):207303-207303
利用射频磁控溅射法在(LaAlO3)0.3(SrAl0.5Ta0.5O3)0.7 (001)单晶基底上生长了镧掺杂BaSnO3外延薄膜. 通过Hall效应和热电势测量证实了镧掺杂BaSnO3薄膜具有n型简并半导体特征, 并且基于载流子浓度和Seebeck系数计算出电子的有效质量为0.31m0 (m0为自由电子质量). 镧掺杂BaSnO3薄膜在可见波段具有良好的透明性(透过率大于73%). 基于介电模型对薄膜的透过率曲线进行拟合, 从拟合结果中不仅得到了薄膜的厚度为781.2 nm, 能带宽度为3.43 eV、 带尾宽度为0.27 eV和复光学介电常数随波长的变化规律, 而且也强力地支持了基于电学参数计算电子有效质量的正确性.  相似文献   

14.
为了得到最长有效余辉时间的Sr_2MgSi_2O_7:Eu~(2+),Dy~(3+)荧光粉,应用二次通用旋转组合设计对实验进行全程优化,建立了稀土离子掺杂浓度Eu~(2+),Dy~(3+)和有效余辉时间的二元二次回归方程模型,应用遗传算法计算得到有效余辉时间的理论最大值.采用高温固相法合成了最优掺杂浓度Sr_2MgSi_2O_7:0.5mol%Eu~(2+),1.0mol%Dy~(3+)的荧光粉,在370nm激发下观察到了465nm的特征发射,这归因于Eu~(2+)的4f65d1—4f7跃迁.测量了最优荧光粉的热释发光特性,计算得到了陷阱深度为0.688eV,讨论了长余辉发光的特性.  相似文献   

15.
In this paper we report studies on a range of niobate based tungsten bronzes, with a view to analysing their potential as anode materials in SOFCs. Six systems were studied, (Sr1−xBax)0.6Ti0.2Nb0.8O3, Sr0.6−xLaxTi0.2+xNb0.8−xO3, (Sr0.4−xBax)Na0.2NbO3, (Ba1−xCax)0.6Ti0.2Nb0.8O3, Ba0.5−xAxNbO3 (A=Ca, Sr), and Ba0.3NbO2.8, and the electrical conductivities were examined over a range of oxygen partial pressures (10−20–1 bar). All the systems showed good conductivity in low oxygen partial pressures, with values as high as 8 S cm−1 at 930°C (P(O2)=10−20 bar). As the oxygen partial pressure was raised the conductivity dropped showing in most cases an approximate [P(O2)]−1/4 dependence and good re-oxidation kinetics. Of all the samples studied the (Sr1−xBax)0.6Ti0.2Nb0.8O3 and (Ba1−xCax)0.6Ti0.2Nb0.8O3 systems appear most promising for potential use as anode materials in SOFCs.  相似文献   

16.
The complex electrical impedance of Na3H(SO4)2 along the bm-axis has been measured from 25°C to 316°C in the frequency range 4 kHz–40 MHz. The temperature dependence of the electrical conductivity shows remarkable changes in the temperature range 160°C–260°C. The sample crystal becomes a fast ionic conductor above 260°C. The conduction mechanisms of proton and sodium ions in the different phases are analyzed in detail with respect to the structural features of the sample crystal.  相似文献   

17.
Epitaxial thin films of Fe3O4 and CoFe2O4 on MgO (0 0 1) substrates were grown by molecular beam epitaxy at low temperature growth process. Magnetization and hysteresis loop of both films were measured to investigate magnetic anisotropic properties at various temperatures. Anomalous magnetic properties are found to be correlated with crystalline, shape, and stress anisotropies. The Fe3O4 film below Verwey structural transition has a change in crystal structure, thus causing many anomalous magnetic properties. Crystalline anisotropy and anomalous magnetic properties are affected substantially by Co ions. The saturation magnetization of Co–ferrite film becomes much lower than that of Fe3O4 film, being very different from the bulks. It indicates that the low temperature growth process could not provide enough energy to have the lowest energy state.  相似文献   

18.
In this study, we will develop the influences of the excess x wt% (x=0, 1, 2, and 3) Bi2O3-doped and the different fabricating process on the sintering and dielectric characteristics of 0.95 (Na0.5Bi0.5)TiO3–0.05 BaTiO3 ferroelectric ceramics with the aid of SEM and X-ray diffraction patterns, and dielectric–temperature curves. The 0.95 (Na0.5Bi0.5)TiO3–0.05 BaTiO3+x wt% Bi2O3 ceramics are fabricated by two different processes. The first process is that (Na0.5Bi0.5)TiO3 composition is calcined at 850 °C and BaTiO3 composition is calcined at 1100 °C, then the calcined (Na0.5Bi0.5)TiO3 and BaTiO3 powders are mixed in according to 0.95 (Na0.5Bi0.5)TiO3–0.05 BaTiO3+x wt% Bi2O3 compositions. The second process is that the raw materials are mixed in accordance to the 0.95 (Na0.5Bi0.5)TiO3–0.05 BaTiO3+x wt% Bi2O3 compositions and then calcining at 900 °C. The sintering process is carried out in air for 2 h from 1120 to 1240 °C. After sintering, the effects of process parameters on the dielectric characteristics will be developed by the dielectric–temperature curves. Dielectric–temperature properties are also investigated at the temperatures of 30–350 °C and at the frequencies of 10 kHz–1 MHz.  相似文献   

19.
The comparative study of MgB2 film growth on Al2O3 and glass substrate by electrocrystallization technique is discussed. The precursor magnesium films were deposited by vacuum evaporation method. These magnesium films were then used as electrode for the growth of MgB2 films by electrocrystallization. The structural, morphological and superconducting properties of the electrocrystallized MgB2 films on Al2O3 substrate were examined by using XRD, SEM and electrical resistivity measurement techniques and compared with that of MgB2 films grown on glass substrate. The films deposited on Al2O3 substrates showed enhanced crystallinity and relatively higher Tc value compared to films deposited on glass substrates.  相似文献   

20.
We investigated the effect of an electric-pulse on the insulator–metal phase transition of VO2/Al2O3 films using synchrotron-based infrared microspectroscopy. By monitoring the time-resolved optical response, we could demonstrate that local conducting areas are formed under the influence of the electric-pulse, and the Joule heat generated from the local current flow drives a consecutive thermal phase transition in the adjacent sample area.  相似文献   

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