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1.
The n = 2 Aurivillius phase Bi 2 − xPb xSr 1 − xNd 2O 9 was successfully synthesized as a ceramic material over the whole range of simultaneous, charge compensated substitution x = 0–1.0. Structural investigations were performed by Rietveld refinement applying different space groups Fmmm and A2 1am, and additionally by X-ray absorption spectroscopy (EXAFS) on the Nd L III-edge, confirming the accommodation of Nd on the atomic sites of Sr, which implies the substitution of Bi 3+ by the isoelectronic Pb 2+. The ferroelectric transition temperature Tc = 270 °C of the substituted powders with x = 0.4 and 1.0 is distinctly reduced compared to the unsubstituted sample with Tc = 450 °C. In temperature resolved powder X-ray diffraction patterns no structural phase transition could be detected. 相似文献
2.
Measurements of magnetization and 57Fe Mössbauer spectra have been made for Y(Fe 1−xRu x) 2. The C15 type cubic structure is stabilized for x0.06 and the C14 type hexagonal structure for x 0.7. The C15 compounds is ferromagnetic with Tc200 K and its saturation moment decreases monotonically with increasing x, while the 57Fe hyperfine field decreases only slightly with x. From these results, it is deduced that the Ru atoms have an induced moment of ≈1μ B in the range x 0.2. In the C14 type phase, no magnetic ordering develops even at 4.2 K. 相似文献
3.
Phase evolution in the Bi---Sr---Ca---Cu---Al---O system was studied. Two Al-containing phases BiSr 1.5Ca 0.5Al 2O z and (Sr 1−xCa x) 3Al 2O 6 ( x = 0.4 − 0.45) were determined to be chemically compatible with Bi 2.18Sr 2CaCu 2O 8+x (Bi-2212) at temperatures of the samples processing. The phase equilibria in the title system were investigated above the solidus temperature. The BiSr 1.5Ca 0.5Al 2O z was found to be in equilibrium only with the melt and the (Sr 1−xCa x) 3Al 2O 6 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 + BiSr 1.5Ca 0.5Al 2O z ↔ (Sr 1−xCa x) 3Al 2O 6 + liquid. Two sets of superconducting composite materials with initial compositions Bi-2212 + nBiSr 1.5Ca 0.5Al 2O z and Bi-2212 + m(Sr 1−xCa x) 3Al 2O 6 were prepared by solidification from the partial melt. The former material was composed mostly of large Bi-2212 lamellas separated by the BiSr 1.5Ca 0.5Al 2O z 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 (Sr 1−xCa x) 3Al 2O 6 imbedded in Bi-2212 lamellas. The Bi-2212 + m(Sr 1−xCa x) 3Al 2O 6 materials displayed a trend to enhance flux pinning at T = 60 K with the increase of aluminate phase content. 相似文献
4.
Samples of NbSr 2Gd 2−xCe xCu 2O y have been prepared by solid state reaction. The X-ray powder diffraction patterns show that a single phase can be formed in the composition range of 0.49< x<0.51 that has TaSr 2 (NdCe) 2Cu 2O y structure [1], the cell parameters being a=3.8669±0.0046 Å and c=28.742±0.0048 Å. Superconductivity was found by resistance measurements in the sample of NbSr 2Gd 1.5Ce 0.5Cu 2O y: the onset transition temperature is 27.4 K, and zero resistance appears at approximately 13 K. 相似文献
5.
The effects of Fe-substitution of YBa 2Cu 3O y have been investigated by means of Raman scattering, X-ray diffraction, resistivity and susceptibility measurements. A series of samples of YBa 2(Cu 1 − xFe x) 3O y with different dopant concentration (0 x 0.15) has been prepared in two batches, the second set having undergone twice the heat and mechanical treatment used to produce the first batch. Considerable improvement in the superconducting transition temperature, Tc, is obtained upon reprocessing. A phase transformation from orthorhombic to tetragonal symmetry is observed for x=0.05 from the X-ray measurements in agreement with previous work. Using a micro-Raman technique, all five A g vibrational modes have been measured and their dependence on Fe-concentration is analyzed. There are indications that iron substitutes for copper at both sites and that the structure is a mixture of orthorhombic and tetragonal microdomains for all x. 相似文献
6.
Lattice spacings, as magnetic susceptibilities, ESR, specific heats, and electrical properties have been measured on the cointercalation compounds of 1T-CdI 2 type host TiS 2, Fe xCo
TiS 2 (0 x
) and (Fe yCo 1−y)
TiS 2(0 y 1). While the interlayer spacings are expanded rather smoothly with increasing the cointercalated Fe metals, the magnetic, thermal, and transport properties depend sensitively on a small amount of the added Fe metals, showing the presence of strong magnetic interactions, or guest-guest interactions between the cointercalated Fe and Co 3d metals in these systems. 相似文献
7.
Magnetic transitions in La(Fe 1−xCo x) 11.4Si 1.6 compounds with x=0–0.08, have been studied by DC magnetic measurements and Mössbauer spectroscopy. The temperature dependence of the Landau coefficients has been derived by fitting the magnetization, M(μ 0H), using the Landau expansion of the magnetic free energy. For x0.02 there is a strongly first-order magnetic phase transition between ferromagnetic and paramagnetic (F–P) states in zero external field and a metamagnetic transition from paramagnetic to ferromagnetic (P–F) above Tc. Increasing the cobalt content drives the F–P transition towards second order and eliminates the metamagnetic transition. 相似文献
8.
(Ba 1−xLa x) 2In 2O 5+x, whose end member is Ba 2In 2O 5, is an oxygen-deficient perovskite oxide showing high oxide-ion conductivity. In order to clarify the reason why the high oxide ion conductivity appeared in this system, the electrical conductivity was measured as a function of temperature and La content. With an increasing La content, the discontinuous jump of ion conductivity in the Arrhenius plot, which is related to the disordering of the oxygen vacancies, disappeared for the sample with x0.2. Above x=0.12, the ion conductivity linearly increased with La content, while the activation energy remained constant with respect to the La content. Moreover, the conductivity for x=0.6 was 0.042 (S/cm) at 1073 K, which exceeded that of 8 mol% yttria-stabilized zirconia. The higher oxide-ion conductivity of this system could be dominated by the amount of mobile oxygen ions. 相似文献
9.
The electrical conductivity of the LaY 1−xIn xO 3 ( x=0.0–0.7) system has been studied from the viewpoint of crystal chemistry. The high temperature form of LaYO 3 ( x=0.0) was ascertained to be the Sm 2O 3-type (B-type rare earth) structure, not perovskite-type one. The X-ray diffraction (XRD) experiments revealed that the samples with x=0.05 and 0.10 were the mixed phase of Sm 2O 3-type and perovskite-type structure, and changed to perovskite phase in the range of x0.20. From oxygen partial pressure dependence of the electrical conductivity, it was found that both the Sm 2O 3-type and the perovskite-type single phases showed hole conduction, but the mixed phase did oxide-ion one. The electrical conductivity of the LaY 1−xIn xO 3 ( x=0.0–0.7) system increased with increasing x, and showed the maximum value in the range of x=0.05–0.10, and then decreased with increasing x. The occurrence of oxide-ion conduction was discussed from the viewpoint of lattice distortion in the mixed phase. 相似文献
10.
Magnetic characteristics of Ti-, Zr- and Hf-substituted PrCo 5 alloys have been studied over the temperature range from 77 to 300 K and for applied fields up to 20 kOe. It is established that Ti, Zr and Hf substitute for Pr. Single-phase materials are formed for all values of x up to 0.2 in the system Pr 1−xZr xCo 5 but for x only up to 0.1 for Pr 1−xTi x Co 5 and Pr 1−xHf xCo 5 alloys. Larger amounts of Zr can be substituted if the material is made hyperstoichiometric in Co, e.g., Pr 0.7Zr 0.3Co 5.5. All the alloys show a decrease in magnetic moment and an increase in Curie temperature as x increases. Anisotropy fields decrease as x increases at 295 K. Anomalous behavior is observed at 77 K, suggested that these ternary alloys may have a cone structure at this temperature. 相似文献
11.
用多体势结合分子动力学计算了L1 2型NiAl 3, L1 2型Ni 3Al, L1 0型NiAl和B 2 型NiAl的晶格常数, 结合能以及合金形成热; 分析了结构性点缺陷在上述四种合金中的存在形式; 在此基础上研究了合金化元素Mo, Ta, W在Ni xAl 1-x( x=0.25,0.5,0.75)中的择优占位行为. 计算结果表明: 对于四种结构的Ni-Al合金, 偏离理想化学配比时,主要的结构缺陷形式是反位置; 根据占位能最小化, 第三组元元素Mo, Ta, W在上述四种Ni-Al中都显著优先占据Al格位.
关键词:
多体势
Ni-Al合金
占位 相似文献
12.
R 2(Fe, Co) 14B compounds (R = Y, Nd and Gd) were prepared in high purity. The magnetic behavior of R 2(Fe, Co) 14B compounds is reported over the temperature range 4 to 300 K. The effects of Fe substitution by Co on the saturation magnetization, Curie temperature and anisotropy are presented. The spin-reorientation temperature is lowered as Co replaces Fe. This also results in a reduced cone angle. The R2Fe14−xCoxB alloys crystallize in the tetragonal structure over the entire concentration range of 0 x 14. When Fe is substituted by Co, the Curie temperature increases significantly, the saturation magnetization increases to a maximum value around x = 2, and the anisotropy becomes planar for R = Y and Gd. The Nd2(Fe, Co)14B systems all exhibit uniaxial anisotropy at room temperature and Nd2Co14B is strongly uniaxial at 77 K. The Nd2(Fe, Co)14B systems are conical at 77 K. 相似文献
13.
The appearance of ferromagnetism in Y(Co 1−xAl x) 2 is discussed in terms of a d band model. The approximate d bands for YCo 2 and Y(Co 1−x) 2 are calculated and the decrease in the electronic energy due to magnetization of the spin of estimated. The energy decrease is the largest in YCo 2, and it gradually decreases as the Al content increases, if the lattice constant is fixed, while this energy decrease increases if the lattice constant increases with increasing Al content. These results of calculations give a good account of the appearance of ferromagnetism in Y(Co 1−xAl x) 2 around x = 0.15. The ferromagnetism in Sc(CO 1−xAl x) 2 is also discussed, leading to the appearance of ferromagnetism between x = 0.15 and 0.30. 相似文献
14.
Structure and magnetic properties of the Zr 1−xMn xCo 2+δ alloys were studied for 0 x <0.7, δ=0, 0.45. The cubic C15 Laves phase structure shows Mn solubility up to x≈0.4. The other Laves phase with the hexagonal C36 structure found for x0.5 apparently has a small region of Mn solubility in the vicinity of Zr 0.4Mn 0.6Co 2. Though the parent Mn-free compounds are known to be paramagnetic, the Mn-substituted alloys show ferromagnetic behavior with the Curie temperatures up to 625 K and the room-temperature saturation magnetization of about 100 emu/g. The onset of ferromagnetism with the Mn substitution for Zr may be caused by polarization of itinerant 3d electrons, like it was earlier supposed for the off-stoichiometric ZrCo 2+δ. The universal composition dependencies of the intrinsic magnetic properties for different δ can be obtained, if plotted against the amount of zirconium atoms missing in its sublattice. The room-temperature anisotropy with the noticeable anisotropy field of 24 kOe and the 1 1 0 easy magnetization direction laying in a basal plane was found in the hexagonal Zr 0.5Mn 0.5Co 2. 相似文献
15.
New Scheelite-related solid solutions of the compositions Na x/2Bi 1−x/2Mo xV 1−xO 4 (0≤ x≤1) and Bi 1−x/3 Mo xV 1−xO 4(0≤ x≤0.2) have been synthesised by the substitution of Na and Mo at the A and B sites respectively of the ABO 4 type ferroelastic BiVO 4. The phases were characterised using chemical analysis, powder X-ray diffraction, scanning electron microscopy, EDAX, and Raman spectroscopy. While almost a continuous solid solution is obtained for the series Na x/2Bi 1−x/2Mo xV 1−xO 4, the absence of Na at the A-site results only in a narrow stability region for the other series, Bi 1−x/3 Mo xV 1−xO 4 where 0≤ x≤0.2. Raman spectra of selected samples at room temperature also suggest that vanadium and molybdenum atoms are disordered at the tetrahedral sites. 相似文献
16.
We have made high-temperature (250 K< T<800 K) DC susceptibility measurements in the compounds RuSr 2Eu 2−xCe xCu 2O 10 for x=0.6,0.8, and 1.0 in order to determine the Ru effective magnetic moment. After carefully subtracting all contributions to the magnetic susceptibility except that of the Ru ions, we have been able to fit the Ru susceptibility with a law χ Ru=χ 0+ CRu/( T−Θ Ru). We have found that the Ru effective moment
falls between the values expected for Ru 5+ in spin states
and
. We have also found a dependence of μ eff(Ru) and Θ Ru with the Ce content x. 相似文献
17.
The magnetic phase diagram of La 2(Cu 1−xZn x)O 4 has been determined from zero-field muon-spin-rotation (ZF-μSR) data taken at LAMPF for 0 ≤ x ≤ 0.10. Antiferromagnetic onset temperatures follow TN( x) from susceptibility measurements on the same samples. However, the order becomes long range, as evidenced by a well-defined internal magnetic field, only at temperatures well below TN. Extrapolation of our results yields TN → 0 K at x = 0.11 for a single (Cu 1−xZn x)O 2 plane, and comparison with YBa 2(Cu 1−xZn x) 3O 6 implies identical disruption of magnetism by Zn doping in the single- and double-plane systems. 相似文献
18.
Materials from the Mn (0.5−x)Ca xTi 2(PO 4) 3 (0≤ x≤0.50) solid solution were obtained by solid-state reaction in air at 1000 °C. Selected compositions were investigated by powder X-ray diffraction analysis, 31P nuclear magnetic resonance (NMR) spectroscopy and electrochemical lithium intercalation. The structure of all samples determined by Rietveld analysis is of the Nasicon type with the R
space group. Mn 2+/Ca 2+ ions occupy only the M1 sites in the Ti 2(PO 4) 3 framework. The divalent cations are ordered in one of two M1 sites, except for the Mn 0.50Ti 2(PO 4) 3 phase, where a small departure from the ideal order is observed by XRD and 31P MAS NMR. The electrochemical behaviour of Mn 0.50Ti 2(PO 4) 3 and Mn (0.5−x)Ca xTi 2(PO 4) 3 phases was characterised in Li cells. Two Li ions can be inserted without altering the Ti 2(PO 4) 3 framework. In the 0≤ y≤2 range, the OCV curves of Li//Li yMn 0.50Ti 2(PO 4) 3 cells show two main potential plateaus at 2.90 and 2.50–2.30 V. Comparison between the OCV curves of Li//Li (1+y)Ti 2(PO 4) 3 and Li//Li yMn 0.50Ti 2(PO 4) 3 shows that the intercalation occurs first in the unoccupied M1 site of Mn 0.50Ti 2(PO 4) 3 at 2.90 V and then, for compositions y>0.50, at the M2 site (2.50–2.30 V voltage range). The effect of calcium substitution in Mn 0.50Ti 2(PO 4) 3 on the lithium intercalation is also discussed from a structural and kinetic viewpoint. In all systems, the lithium intercalation is associated with a redistribution of the divalent cation over all M1 sites. In the case of Mn 0.50Ti 2(PO 4) 3, the stability of Mn 2+ either in an octahedral or tetrahedral environment facilitates cationic migration. 相似文献
19.
High field magnetization measurements have been performed to examine the existence of itinerant metamagnetism in exchange-enhanced systems related to YCo 2 together with Fe 1−x Co xSi. In the Y(Co −xFe x) 2 system, the meta magnetism inherent in YCo 2 has been observed in 0.04 x0.07. The transition is not as sharp as in the Y(Co 1−xAl x) 2 system. Other exchange-enhanced paramagnets Y(Co −xCu x) 2 and Y 1−xLa xCo x2 and weakly itinerant ferromagnet Fe 1−xCo xSi exhibit no metamagnetic transition up to 430 kOe. 相似文献
20.
为了研究钙钛矿结构的SrTiO_3固化Y~(3+)(~(90)Y的模拟物)的化学稳定性,以Sr(NO_3)_2,TiO_2及Y_2O_3粉体作为原料,按照化学计量比Sr_(1-1.5x)Y_xTiO_3(0≤x≤0.12)设计配方,采用高温固相法制备一系列固化体.利用X射线衍射、扫描电镜和Raman对制备固化体的物相、结构和微观形貌进行分析表征,并对其抗浸出性能进行了研究.结果表明:当x0.08时,固化体为单一物相,当x≥0.08时,固化体中出现部分烧绿石相;固化体中的Sr~(2+),Y~(3+)的浸出浓度随浸泡时间延长而增大,在浸泡42d时,Sr~(2+)的最大浸出浓度为0.004μg·mL~(-1),Y~(3+)的最大浸出浓度为0.02μg·mL~(-1). 相似文献
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