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1.
Variation of the complex permeability with frequency of Ni 1−xZn xFe 2O 4 ( x=0.5, 0.6 and 0.7) prepared by a combustion method has been measured over a wide range of frequency, up to 1.8 GHz. Zn content improves permeability but moves the onset of resonance to lower frequencies. The influence on some properties of samples prepared by the insertion of small amounts of Ruthenium, Yttrium and rare-earth cations into the Ni0.5Zn0.5MxFe2−xO4 ferrite has been also investigated. Relative losses and Curie temperature of all the samples have been measured. Ferrites substituted with Ru and Gd improve microwave behavior compared to non-substituted samples. 相似文献
2.
Samples of Bi 2Sr 2Ca 1−xPr xCu 2O y have been characterized by resistivity and thermoelectric power measurements. All metallic samples show superconductivity with a maximum Tc = 90 K at X = 0.2. The sample of x = 0.6 shows a crossover from hopping conduction at low temperature above Tc to metallic conduction at high temperature. For the metallic samples below x = 0.6, the results of thermoelectric power are well fitted by both of a phenomenological band spectrum model and the Nagaosa and Lee model. 相似文献
3.
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
4.
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
5.
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
6.
In order to understand the mechanism that gives rise to superconductivity in the ceramic superconductors of the type Ba xK 1 − xBiO 3, we analyze the thermodynamic properties with the use of the Eliashberg equations. For these calculations we used the electron-phonon spectral density function 2(ω) F(ω), calculated by Shirai et al. [1] from first principles for two different K concentrations, x=0.5 and x=0.7. 相似文献
7.
The structural, electrical and magnetic properties of the superconducting ferromagnets, Gd 1.4−xDy xCe 0.6Sr 2RuCu 2O 10 ( x=0–0.6) are systematically investigated as a function of Dy doping and temperature. These compounds are characterized by high temperature superconductivity ( Tc ranging from 20 to 40 K depending upon the Dy content) co-existing with weak ferromagnetism with two magnetic transitions ( TM2 ranging from 95 to 106 K and TM1 around 120 K). Doping with Dy gives no significant structural changes except for a minor change in the c/ a ratio. However the superconducting transition temperature is significantly suppressed and magnetic ordering temperature enhanced on Dy doping. These effects are described and discussed. 相似文献
8.
A series of samples Pr 0.6−xSr 0.4MnO 3 ( x=0, 0.01, 0.05, 0.1, 0.15, 0.2) were synthesized by a solid state reaction method. Pr deficiency at the A site has a great effect on the properties of Pr 0.6−xSr 0.4MnO 3 as the cathode of SOFCs (solid oxide fuel cells). Compared to the commonly used La 0.6Sr 0.4MnO 3 and La 0.55Sr 0.4MnO 3 cathode, Pr 0.6−xSr 0.4MnO 3 is better in the properties of conductivity, overpotential and impedance. In all the samples, the one with x=0.05, Pr 0.55Sr 0.4MnO 3, revealed the best performance in the measured temperature range. 相似文献
9.
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
10.
Oxygen tracer diffusion ( D*) and surface exchange rate constant ( k*) have been measured, using isotopic exchange and depth profiling by secondary ion mass spectrometry (SIMS), in La 1−xSr xFe 0.8Cr 0.2O 3−δ ( x=0.2, 0.4 and 0.6). Measurements were made as a function of temperature (700–1000 °C) and oxygen partial pressure (0.21–10 −21 atm) in dry oxygen, water vapour and water vapour/hydrogen/nitrogen mixtures. At high oxygen activity, D* was found to increase with increasing temperature and Sr content. The activation energies for D* in air are 2.13 eV ( x=0.2), 1.53 eV ( x=0.4) and 1.21 eV ( x=0.6). As the oxygen activity decreases, D* increases as expected qualitatively from the increase in oxygen vacancy concentration. Under strongly reducing conditions, the measured values of D* at 1000 °C range from 10 −8 cm 2 s −1 for x=0.2 to 10 −7 cm 2 s −1 for x=0.4 and 0.6. The activation energies determined at constant H 2O/H 2 ratio are 1.21 eV ( x=0.2), 1.59 eV ( x=0.4) and 0.82 eV ( x=0.6). The surface exchange rate constant of oxygen for the H2O molecule is similar in magnitude to that for the O2 molecule and both increase with increasing Sr concentration. 相似文献
11.
Magnetization and Curie temperature of Y xZr 1−xCo 2.9 decrease with decreasing x. Their hydrides with x0.8 are paramagnetic with an anomaly and those of 0.7 x0.5 become weak ferromagnets. The spin structure is discussed. 相似文献
12.
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
13.
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
14.
By making use of high-temperature series expansions (HTSE) of the correlation functions, we study the thermal and disorder variation of the short-range order (SRO) in the particular B-spinel ZnCr 2xAl 2−2xS 4. We developed the HTSE for the q-dependent static structure factor S( q) to the order 6 in reciprocal temperature including both the nearest- and next-nearest-neighbour interactions J1 and J2, respectively. Respecting the experimental fact that the broad diffuse peak of the neutron is situated at the particular wave vector q0=[0 0 0.79] and is insensitive to the temperature for a given ratio of dilution x, we have estimated the thermal variation of J1 and J2 in the case of the pure compound. The bond percolation threshold xp of the ZnCr2xAl2−2xS4 is determined by studying the disorder variation of the correlation length ξ. The xp is considered as the concentration at which ξ vanishes. The obtained values are xp=0.27 when only J1 is considered and 0.23 when both J1 and J2 are taken into account. 相似文献
15.
Ceramic samples of Ca 1−xY xMnO 3 were synthesized by a liquid-mix method obtaining single phase materials, for 0.1 x1, with orthorhombic structure. The cell volume increases with x indicating that changes in the Mn electronic state overcomes the progressive diminishing of the (Ca, Y) cationic radius, rCa> rY. We observed a continuous broadening of the electronic spin resonance line width with x. This is explained in terms of the increasing orthorhombic distortions. We have measured the DC magnetization for the x=1 compound YMnO 3. Our results are compatible with a G-type antiferromagnet with TN=44 K. 相似文献
16.
The crystallographic, magnetic and magneto-optical properties of Heusler compounds of the type Ni 3-xMn xSn were investigated. The thermal expansion behaviour of a limited number of these compounds was also studied. The cubic L2 1 structure was found to exist in the range 0.6 x 2.2. With increasing x the saturation moment first increases, then decreases again. The main peak in the Kerr rotation spectra measured in the energy range 0.5-4.5 eV shows a similar trend. The Curie temperature and the lattice constant increase with x, both quantities showing a discontinuity near x = 1. All these features are discussed in terms of relative site occupancies of the Mn atoms at the tetrahedral and octahedral sites in the L2 1 structure. 相似文献
17.
The dielectric constant (′) and dielectric loss (tan δ) for hexaferrites BaCo 2−xZn xFe 16O 27 have been studied as a function of frequency ( f), temperature ( T) and composition ( x). The experimental results indicate that ′ and tan δ above the relaxation frequency only decrease as the frequency increases and as the temperature decreases. Tan δ shows the dielectric relaxation at certain critical frequencies which rise as temperature increases. The activation energy for the dielectric relaxation ( ED), ′, and tan δ are found to be minimum for x = 0.8. 相似文献
18.
On the basis of chemical, thermal analysis and Cu K-edge X-ray absorption measurements, oxygen content in the Nd 1+xBa 2−xCu 3O z solid solution was determined between 1000°C in air and 400°C in oxygen for x=0.05–0.9 compositions. It has been observed that the oxygen nonstoichiometry Δ z of the Nd 1+xBa 2−xCu 3O 7+x/2−Δz solid solution decreases 2–2.5 times for a large substitution (Δ z≈0.3–0.33 for x=0.9), despite of the acclaimed higher total oxygen content. The difference in nonstoichiometry is explained by a higher average value of the copper oxidation state (ACV), which is vital for the solid solution with large x even at elevated temperatures (ACV≈2–2.05 for x>0.3 at 1000°C, PO 2=0.21 atm). On the contrary, the ACV after complete oxygenation is almost constant (about 2.25–2.3) for the whole series. The x-dependence of the oxygen content is not monotonous and structural phase transitions can be observed at x=0.3 and x=0.6, as confirmed by the X-ray diffraction and the Raman scattering spectroscopy. The first well-known transition is connected with the oxygen disorder due to the Nd substitution for Ba at random Ba-sites. In the present work, it is proved by the apical oxygen mode broadening in Raman spectra. Ordering of the Nd and Ba atoms with a subsequent orthorhombic distortion of the lattice may occur even at 1000°C in air due to the second transformation at x≈0.6. The invariable orthorhombicity of the Nd-rich solid solution with x>0.6 is not caused by the oxygen absorption as in the x=0.05 case. Existence of high- and low-temperature orthorhombic modifications of this solid solution has been observed for the first time. Finally, a tentative 3D ( z– x– T) diagram is suggested for the Nd 1+xBa 2−xCu 3O z solid solution up to 1000°C in air, including the new x=0.6–0.9 region. 相似文献
19.
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
20.
采用溶胶凝胶法制备Bi 1-xCa xFeO 3 (x=0, 0.05, 0.1, 0.15, 0.2)陶瓷样品. X衍射图谱表明所有样品的主衍射峰均与纯相BiFeO 3相符合且具有良好的晶体结构. 随着x的增大, Bi 1-xCa xFeO 3样品的主衍射峰由双峰(104)与(110) 逐渐重叠为单峰(110), 当x ≥0.15时, 样品呈现正方晶系结构; 扫描电镜形貌分析可知, 晶粒由原来的0.5 μm逐渐增大到2 μm. Bi 1-xCa xFeO 3样品介电常数和介电损耗随着x 的增加先增大而后减小. 当f=1 kHz, Bi 0.9Ca 0.1FeO 3 的介电常数达到最大值, 是BiFeO 3的7.5倍, 而Bi 0.8Ca 0.2FeO 3的介电常数达到最小值, 仅仅是BiFeO 3的十分之一. Bi 1-xCa xFeO 3样品所呈现的介电特性是由偶极子取向极化和空间电荷限制电流两种极化机理共同作用的结果. 随着Ca 2+ 的引入, BiFeO 3 样品的铁磁性显著提高. X射线光电子能谱图表明Fe 2+和Fe 3+ 共存于Bi 1-xCa xFeO 3 样品中, Fe 2+/Fe 3+比例随着Ca 2+ 掺杂量的增加而增大, 证明Ca 2+掺杂增加了Fe 2+的含量, 增强BiFeO 3的铁磁特性. 从 M-T曲线观察到BiFeO 3样品在878 K附近发生铁磁相变, 示差扫描量热法测试再次证明BiFeO 3 在878 K发生相变. Ca 2+掺杂使BiFeO 3样品的 TN略有变化而 TM基本不变, 其主要原因是Fe-O-Fe反铁磁超交换作用的强弱和磁结构相对稳定. 相似文献
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