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1.
The temperature-composition ( T– x) phase diagram and NFL characteristics in the electrical resistivity ρ( T), specific heat C( T), and magnetic susceptibility χ( T) at low temperatures for the systems U 1−xM xPd 2Al 3 (M=Y,Th) are described. The T– x phase diagram, the NFL characteristics, and the underlying mechanism for the NFL behavior are distinctly different for M=Y 3+ and Th 4+, apparently reflecting the difference in valence of the M atom substituents, and suggesting that U is tetravalent in these two systems. 相似文献
3.
The polarized Raman spectra of Nd 1+xBa 2−xCu 3O 7−δ (−0.023≤ x≤0.107) and Pr 1+xBa 2−xCu 3O 7−δ (0.01≤ x≤0.15) single crystals have been investigated. It was found that the Cu(2) Ag mode softens by 6 cm −1 in Nd 1:2:3 and 4 cm −1 in Pr 1:2:3 as x increases. These frequency shifts cannot be explained by the change in the relevant bond lengths due to Nd(Pr)-substitution for Ba. The variations with x of the two low frequency modes may be affected by change of their hybridization and/or change of their force constants. The linewidths of Ba mode in Pr 1:2:3 are broader than those in Y 1:2:3. This result suggests that the Pr substitution on Ba sites occurred even in a very small value of x. In x( yy)
geometry the relative intensity of the Ba and O(4) modes in Nd 1:2:3 is greater than those in Pr 1:2:3. The difference between Nd 1:2:3 and Pr 1:2:3 in the relative intensity of the Ba and O(4) modes may be produced by the chains. 相似文献
4.
In this article we present a concise report on our studies on the magnetic behavior and structural arrangements of the inverse spinel Zn 7−xM xSb 2O 12 system (M=Ni, Co). Studies on the temperature dependence of the magnetization ( M) of several samples in this system showed the occurrence of a spin-glass-like state in temperatures around 10 K. The capability of this system to hold magnetic ions in either octahedral and/or tetrahedral positions is responsible for the occurrence of competing ferromagnetic and antiferromagnetic interactions. This condition is likely to cause the appearance of the observed spin-glass-like behavior. 相似文献
5.
Single crystals with known Tc values of Y 1−xPr xBa 2Cu 3O 7−δ (Y---Pr1:2:3) and YBa 2Cu 3−xZn 3−xZn xO 7−δ (Y---Zn1:2:3) systems are studied by Raman measurements. The Raman spectra for (Y---Pr1:2:3) single crystals show that the frequencies of Ba and O z modes increase as the Pr content increases. The results are consistent with the hole-localization scheme proposed for the suppression of superconductivity in the polycrystalline Y---Pr1:2:3 systems. On the other hand, in the Y---Zn1:2:3 system, all the Raman modes do not change in frequencies. However, the FWHM of the Cu(2) mode increases with the decrease of Tc, indicating strong scattering of charge carriers by the substituted Zn ions in the CuO 2 planes. The induced disorder in the CuO 2 planes may be related with suppression of Tc in the Y---Zn1:2:3 system. Thus, the suppression mechanism in the Y---Zn1:2:3 systems seems to be different from that in the Y---Pr1:2:3 systems. 相似文献
6.
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
7.
The superconductivity of Tl 0.5Pb 0.5Sr 2−xNd xCuO 5−δ was observed for x ≥ 0.3, although the calculated Cu valence assuming Tl 3+ and Pb 4+ is slightly above or below 2.0. The binding energy of the Tl and Pb 4f core levels measured by XPS shifted to higher energy than those of Tl 3+ and Pb 4+ in the reference materials, showing that the Tl and Pb valences are lower than 3 + and 4 +, respectively. These observations strongly suggest that holes in the CuO 2 sheet are created by charge transfer from the (Tl,Pb)O layer, similar to the double-layered Tl---Ba cuprates. In contrast, the temperature variation of electrical conductivity of Tl0.5Pb0.5Sr2CuO5−δ changed from metallic to semiconducting with increasing oxygen deficiency, δ, and no superconductivity was observed through any control of δ. Although XPS measurement also suggested that Tl and Pb valences lowered with increasing oxygen deficiency, δ, the reason why the system did not show superconductivity can be understood by the depletion of oxygen from the CuO2 plane during deoxygenation. 相似文献
8.
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
10.
Magnetic and low temperature specific heat measurements have been performed on iron doped YBa 2(Cu 1−xFe x) 3O 7−δ samples with different oxygen contents (δ0 and δ1). Iron doping induces an orthorhombic to tetragonal transition and a decrease of both Tc and diamagnetic signal. Low temperature specific heat measurements reveal a Schottky type anomaly for δ0 samples with x=0.01 (1.8 K) and x=0.02 (3 K). This anomaly is attributed to magnetic interactions within iron limited chains. A numerical analysis of this effect is proposed. 相似文献
11.
Oxide ion conductivity of the pure and aliovalent ion substituted rare-earth pyrohafnates in the series RE 2−xSr xHf 2O 7 and RE 2Hf 2−xAl xO 7 (RE=Gd and Nd; x=0–0.2) has been explored in the temperature range 400°C–700°C for the first time. It is seen that, conductivity is enhanced by doping 5 atom% Sr at the rare–earth site in these systems. Well defined impedance plots due to grain interior and grain boundary resistances were obtained in the Gd pyrohafnate with Sr substitution. The results of the conductivity variation for the pure, Sr and Al doped phases are explained on the basis of pyrochlore structure. 相似文献
12.
Superconductivity in polycrystalline YBa 2Al xCu (3−x)O 7−δ materials was characterized by dynamic AC and quasistatic DC magnetometry. Intragranular persistent current density and low-loss intergranular critical current density were deduced using DC and AC techniques, respectively. Addition of aluminum produced modest increases in the intragranular persistent current for x < 0.2, but drastically reduced the intergranular critical current density for x = 0.2. The critical temperature Tc for superconductivity decreased only 4% for Al content up to x = 0.2. 相似文献
13.
In this work, luminescence properties of β-(Ga 1−xIn x) 2O 3 solid solutions were investigated with the purpose of making the new thermoluminophors for ultraviolet (UV) dosimetry. The doping of aliovalent cation admixture (Mg, Mo) in the β-Ga 2O 3 ceramic sample brings about the appearance of high-temperature thermoluminescence glow peaks with a maximum at 395 and 435 K. The maximum of the thermoluminophor photosensitivity shifts when the composition of solid solution changes. 相似文献
14.
Perovskite-type La(Cr 1−xMn x)O 3+δ (0.0 x1.0) was synthesized using a sol–gel process. The crystal structure of La(Cr 1−xMn x)O 3+δ changes from orthorhombic to rhombohedral at x=0.6. The Mn 4+ ion content increases monotonically in the range 0.2 x1.0. The magnetic measurement of La(Cr 1−xMn x)O 3+δ indicates that a Mn 3+ ion is a high-spin state with (d ) 3(d γ) 1. The variation of the average (Cr, Mn)-O distance is explained by ionic radii of the Cr 3+, the Mn 3+, the Mn 4+ ions. Since the log σ T–1/ T curve is linear and the Seebeck coefficient ( α) is independent of temperature, it is considered that La(Cr 1−xMn x)O 3+δ is a p-type semiconductor and exhibits the hopping conductivity. 相似文献
15.
Transition temperatures vs. pressure curves of Mn 3Ga 0.9In 0.1C are determined from these results of the temperature dependence of the initial permeability under pressure up to about 7 kbar. For Mn 3Ga 0.98Al 0.02C, the new intermediate magnetic phase appears even in the normal pressure. 相似文献
16.
Based on the singly occupied aiσ picture and the mechanism of charge fluctuation, the effective Hamiltonian of the two-band Hubbard model is derived by using the degeneracy perturbation theory for the noncuprate compound Ba 1−xK xBiO 3. By considering the next-neighbour pairing of two opposite spin holes in coordinate space, the Green's function equation of motion and the superconductivity equation are obtained. Furthermore, how the superexchange interaction and the hopping energy affect the next-neighbour pairing has been reasonably explained, and the superconductivity window is due to the Cooper pairing in coordinate space. 相似文献
17.
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
18.
Layer-type oxide Na xM x/2IITi 1−x/2IVO 2 (M=Co, Ni; 0.60≤ x≤1.0) has been prepared by solid state reactions. In both series, two structural variants of type -NaFeO 2 (O3) and β-RbScO 2 (P2) have been obtained consecutively as x decreases with a borderline composition around xc0.7. With the decrease of x, the ionic conductivity has been found to increase up to 8.4×10 −2 S cm −1 at 770 K (Na 0.67Co 0.33Ti 0.67O 2). Compositions of P2 have been found to exhibit the conductivity values two to five times greater than those of O3, primarily due to the larger rectangular threshold available for the diffusion of Na + ions. Such a structural effect has also been considered to depend on the polarizability of alkali ion. HT-XRD and 23Na-NMR data of Na 0.67Co 0.33Ti 0.67O 2 strongly suggest that the diffusion of Na + ion is deeply related with the local distortion of trigonal prismatic sites, leading to the change of activation energy around 430 K. 相似文献
19.
The flux pinning behavior of a Nd 1+xBa 2−xCu 3O 7−δ (Nd123) single crystal, which exhibited a peak effect, has been studied by monitoring the time decay of the magnetic moment. The apparent pinning energy ( U0*) was deduced from flux creep data on the basis of the Anderson-Kim model. The magnetic field dependence of U0* showed maxima at peak fields which depended on the temperatures, in a similar manner to those of critical current densities. In addition, the temperature dependence of U0* showed several features. To explain the increase in U0* with the field as well as its temperature and field dependence, we made a numerical calculation by introducing an additional pinning energy which increased with increasing field. The results are in good agreement with the experimental data, especially at temperatures above 60 K, where the contribution of field induced pinning centers is believed to be dominant. 相似文献
20.
We present a magnetic study of the insulating perovskite LaMn 1−xTi xO 3+δ (0< x0.2) including measurements of magnetization, susceptibility, and magnetic relaxation. The Curie temperature was found to decrease with increasing content of Ti. Two distinct magnetic transitions, irreversibility, non-exponential relaxation and aging effects confirm a reentrant spin–glass state for x=0.2. The time decay of the magnetization has an algebraic functional form for times up to 2 h. The specific heat also displays characteristic features of a spin–glass system by a linear low-temperature dependence and a broadened peak near the temperature of the reentrant transition. 相似文献
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