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1.
A. M'chirgui 《Solid State Communications》2005,133(5):321-325
A series of polycrystalline samples of Mg1−xPbxB2 (0≤x≤0.10) were prepared by a solid state reaction method and their structure, superconducting transition temperature and transport properties were investigated by means of X-ray diffraction (XRD) and resistivity measurements. Mg1−xPbxB2 compounds were shown to adopt an isostructural AlB2-type hexagonal structure in a relatively small range of lead concentration, x≤0.01. The crystalline lattice constants were evaluated and were found to exhibit slight length compression as x increases. The superconducting transition temperature (Tc) steadily decreases with Pb doping. It is suggested that the mechanism of superconductivity reduction by lead doping can be attributed to the chemical pressure effect. 相似文献
2.
K.J. Syu 《Solid State Communications》2007,141(9):519-522
We have observed superconductivity in the two-phase samples with nominal compositions (Y 1−xThx)NiC2 (x=0.1,0.2,0.3,0.4,0.5). As determined by magnetic, electrical and heat capacity measurements, the superconductivity phase transition temperature Tc increases with Th concentration to . Powder X-ray diffraction data provide the evidence for bulk superconductivity in an orthorhombic CeNiC2-type majority fraction of the sample volume while the minor impurity phase ThC2 has no effect on the superconductivity. The variation of room temperature lattice parameters, a, b, c and v of these substitutional intermetallic samples indicates the systematic substitution of Y 3+ ions by Th4+ ions irrespective of the existence of the 2nd impurity phase. 相似文献
3.
Pseudobinary high Pr-content Tb1−xPrx(Fe0.4Co0.6)1.93 (0.70≤x≤1.00) magnetostrictive alloys have been fabricated by a melt-spinning method. The effects of the composition, spinning, and annealing processes on the structure, thermal stability, and magnetic properties are investigated. At a wheel speed of v≤30 m/s, the as-spun ribbons consist of a mixture of (Tb,Pr)(Fe,Co)2 cubic Laves phase and some non-cubic phases. A single (Tb,Pr)(Fe,Co)2 phase with MgCu2-type structure is formed with the process for the speed of v≥35 m/s and subsequent annealing at 500 °C for 30 min. The lattice parameter of the Tb1−xPrx(Fe0.4Co0.6)1.93 Laves phase increases from 0.7354 nm for x=0.70 to 0.7384 nm for x=1.00 and approximately follows the linear Vegard's law. The Curie temperature decreases, while the saturation magnetization increases as increasing Pr content. The Pr-rich alloys possess the relatively lower coercivity and the faster saturation of magnetostriction as compared with the Tb-rich alloys, which can be understood by their lower magnetic anisotropy. 相似文献
4.
The salt 4-benzyl pyridinium dihydrogenmonophosphate is monoclinic P21/c with the following unit cell dimensions: ; ; ; and β=97.328(11). Also, , Dx=1.403, , F(000)=560; ; and R=0.0495 and Rw=0.0964 for 3733 independent reflections. The structure consists of infinite parallel two-dimensional planes built of H2PO4− anions and C6H5CH2C5H4NH+ cations mutually connected by strong O-H ?O and N-H ?O hydrogen bonding. There are no contacts other than the normal Van der Waals interactions between the layers. The conductivity relaxation parameters associated with some H+ conduction have been determined from an analysis of the spectrum measured in a wide temperature range. 相似文献
5.
We report the effects of partial substitutions of the VIIIa elements: Fe (3d) and Ru (4d) in the intermetallic perovskite superconductor MgCNi3. In both the MgCNi3−xRux and MgCNi3−xFex systems, the superconducting critical temperature (TC) decreases monotonically as x is increased. TC decreases more slowly in the case of Ru, suggesting that the 3d electrons in Fe are magnetically pair breaking. This is supported by the normal state magnetic susceptibility measurements (χ), which shows that χ increases with Fe and decreases with Ru doping. No ferromagnetism is observed in either system. 相似文献
6.
Rajneesh Mohan Kiran Singh Shovit Bhattacharya N.K. Gaur S.K. Gupta 《Solid State Communications》2007,141(11):605-609
Both oxygen and calcium play important roles in inducing superconductivity in Y Ba2Cu3Oy (YBCO), which is an antiferromagnetic insulator at low O and Ca content. O induces superconductivity in Ca-free YBCO, while Ca does similarly in oxygen-deficient YBCO. For doping oxygen HgO was used as it decomposes at 476 °C into Hg, which escapes from the matrix leaving the crystal unaltered, and O, which provide a way to dope O in YBCO. Considering these facts, polycrystalline samples of Y 1−xCaxBa2Cu3Oy with x=0, 0.1 and 0.2 with and without HgO addition were prepared through a solid-state reaction method. The samples were sintered at 950 °C in open atmosphere. These synthesized samples were characterized through using the X-ray diffraction technique (XRD) for phase evaluation, scanning electron microscopy (SEM) for grain morphology, energy dispersive X-ray analysis (EDX) for compositional analysis and the four-contact measurement technique for determining the superconducting transition temperature. 相似文献
7.
F.C. Chou E.T. Abel J.H. Cho Y.S. Lee 《Journal of Physics and Chemistry of Solids》2005,66(1):155-160
We report a detailed study of de-intercalation of Na from the compound NaxCoO2−δ using an electrochemical technique. We find evidence for stable phases with Na contents near the fractions x?1/3, 1/2, 5/8, 2/3, and 3/4. Details regarding the floating-zone crystal growth of Na0.75CoO2 single crystals are discussed as well as results from magnetic susceptibility measurements. We observe the presence of significant oxygen deficiencies in powder samples of Na0.75CoO2−δ prepared in air, but not in single crystal samples prepared in an oxygen atmosphere. The oxygen deficiencies in a Na0.75CoO2−δ sample with δ∼0.08 remain even after electrochemically de-intercalating to Na0.3CoO2−δ. 相似文献
8.
We report a novel, low temperature (450-600 °C) route for the synthesis of highly crystalline and homogeneous nanoparticles of lanthanum calcium manganese oxide La0.67Ca0.33MnO3 (LCMO). The nanocrystallites, with average particle size of 30 nm, possess a ferromagnetic-paramagnetic transition temperature (Tc) of 300 K, which is about 50 K higher than that of a bulk single crystal. The transition temperature was found to be inversely proportional to the particle size. The Rietveld analysis of the powder X-ray diffraction data of the phase-pure nanopowders reveals that the particle size reduction leads to a significant contraction of the unit cell volume and a reduction of the unit cell anisotropy. We propose that these two lattice effects are responsible for the observed enhancement in Tc. 相似文献
9.
J.I. GorinaG.A. Kaljuzhnaia N.N. SentjurinaV.A. Stepanov 《Solid State Communications》2003,126(10):557-561
High-quality undoped Bi2201 single crystals were obtained by free growth in gas-filled cavities formed in the volume of a KCl melt. The superconducting transition temperature Tc was found to be affected by the crystallization temperature Tcryst and varied from 10 to 2 K as Tcryst increased from 840 to 860 °C. The crystals with the highest Tc both in the underdoped and overdoped states were near the maximum of doping curve. 相似文献
10.
S. Sadewasser J.S. Schilling A. Knizhnik G.M. Reisner Y. Eckstein 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,15(1):15-20
Hydrostatic pressure studies on the tetragonal 123 superconductor (La1-xCax) (Ba1.75-xLa0.25+x)Cu3Oy for x
=0.1 and variable oxygen content y show that increases rapidly under pressure (+5 K/GPa) for underdoped, optimally doped and overdoped samples. This points to a common cause for the pressure-induced changes
in the superconductivity at all levels of doping, with negligible effects from charge transfer. Weak relaxation behavior in
is observed only for the most underdoped sample.
Received 26 August 1999 相似文献
11.
We present a systematic study of the structure, magnetization, resistivity, and Hall effect properties of pulsed laser deposited Fe- and Cu-codoped In2O3 and indium-tin-oxide (ITO) thin films. Both the films show a clear ferromagnetism and anomalous Hall effect at 300 K. The saturated magnetic moments are almost the same for the two samples, but their remanent moments Mr and coercive fields HC are quite different. Mr and HC values of ITO film are much smaller than that of In2O3. The ITO sample shows a typical semiconducting behavior in whole studied temperature range, while the In2O3 thin film is metallic in the temperature range between 147 and 285 K. Analysis of different conduction mechanisms suggest that charge carriers are not localized in the present films. The profile of the anomalous Hall effect vs. magnetic field was found to be identical to the magnetic hysteresis loops, indicating the possible intrinsic nature of ferromagnetism in the present samples. 相似文献
12.
13.
M. Kulich P. Ková? M. Eisterer I. Hušek T. Melišek H.W. Weber W. Häßler 《Physica C: Superconductivity and its Applications》2009,469(14):827-831
Effect of 3.4 wt.% C and 5 wt.% SiC doping into the standard in situ (IN) process and mechanically alloyed (MA) MgB2 was studied. Powders of IN and MA process were carried out in air and in argon filled glove box, respectively. Wire samples were prepared by two-axial rolling deformation of IN and MA powders inside the Ti tube. Titanium as sheath material allows to use higher sintering temperatures, we used 700 °C and 800 °C for 30 min in Argon. Critical current densities (Jc) were measured at variable temperatures 4.2 K, 10 K, 15 K and 20 K in the external magnetic fields ranging to 15 T. Critical temperatures, upper critical fields and irreversibility fields of IN and MA with SiC and C additions are compared and discussed. The highest transport properties were observed for wires with MA SiC doped MgB2 in the whole scale of temperatures 4.2–20 K. Upper critical field was rapidly enhanced in the case of carbon doped MA samples at 4.2 K. MA samples have shown decreased Jc values for higher temperatures (15 K, 20 K), in some case even worse than for the not doped reference IN sample. Carbon substitution and grain connectivity of analyzed samples are compared and discussed. Presented results show that for 20 K applications some new ways (additions) have to be found for increasing the Jc substantially. 相似文献
14.
The effect of Cu-doping at Mo-site on structural, magnetic, electrical transport and specific heat properties in molybdates SrMo1−xCuxO3 (0≤x≤0.2) has been investigated. The Cu-doping at Mo-site does not change the space group of the samples, but decreases the structural parameter a monotonously. The magnetic properties change from Pauli-paramagnetism for x=0 to exchange-enhanced Pauli-paramagnetism for x=0.05 and 0.10, and then ferromagnetism for x=0.15 and 0.20. All samples exhibit metallic-like transport behavior in the whole temperature range studied. The magnitude of resistivity increases initially to x=0.10 and then decreases with increasing Cu-doping concentration. The results are discussed according to the electron localization due to the disorder effect induced by the random distribution of Cu at Mo site in the samples. In addition, the temperature dependence of specific heat for the Cu-doped sample has also been studied. 相似文献
15.
The superconducting transition temperatures Tc of face-centered cubic Al1−x-Lix alloys (x=0-0.10) exhibit a minimum near x=0.03 (3 at.% Li). The McMillan strong-coupling Tc equation yields a similar trend of the electron-phonon coupling constant λ. Meanwhile, the density of states at the Fermi level N(0) decreases monotonically with increasing x. It appears that Tc drops initially due to a reduced N(0), which is then overtaken by alloying-enhanced factors of phonon or electron-phonon interaction. 相似文献
16.
Q.Y. Tu X.L. Chen B.K. Ma Z.X. Zhao Y.C. Lan J.K. Liang 《Applied Physics A: Materials Science & Processing》2002,74(1):79-82
An efficient and convenient oxidizing agent, sodium hypochlorite solution, has been used to chemically prepare the superconductor
La2CuO4+δ at room temperature. The crystallographic data show an enhanced orthorhombic distortion and an increase of the unit-cell
volume. The magnetic susceptibility properties reveal a sharp transition beginning at 45 K and the oxidized sample is a homogeneous
and single-phase bulk superconductor. The iodometric titration measurements indicate that the oxidized sample has a higher
excess-oxygen content of 0.11. Scanning electron microscope observations showed that no grain size difference was observed
for the sample before and after oxidation.
Received: 15 September 2000 / Accepted: 19 January 2001 / Published online: 3 April 2001 相似文献
17.
A.G. Kuchin A.S. ErmolenkoYu.A. Kulikov V.I. KhrabrovE.V. Rosenfeld G.M. MakarovaT.P. Lapina Ye.V. Belozerov 《Journal of magnetism and magnetic materials》2006
The magnetic properties have been studied for the series of RNi5−xCux intermetallics with R=Y, La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Lu; x ?2.5. Compositional dependences of magnetic susceptibility for the Pauli paramagnets (R=Y, La, Ce, Lu) and the Curie temperature for ferromagnets (R=Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm) have maximum at x=0.2–0.4 and 1, respectively. The substitution of Cu for Ni is accompanied by decreasing spontaneous magnetic moment and increasing coercive force of all ferromagnetic RNi5−xCux but GdNi5−xCux. These results are explained in the frame of band magnetism, random local crystal field, and domain wall pinning theories. 相似文献
18.
Abhay D. Deshmukh Arti Valechha Animesh Kumar S.J. Dhoble 《Journal of luminescence》2009,129(7):691-162
Nanosized barium aluminate materials was doped by divalent cations (Ca2+, Sr2+) and Eu2+ having nominal compositions Ba1−xMxAl12O19:Eu (M=Ca and Sr) (x=0.1-0.5), were synthesized by the combustion method. These phosphors were characterized by XRD, scanning electron microscopy-energy-dispersive spectrometry (SEM-EDS) and photoluminescence measurement. The photoluminescence characterization showed the presence of Eu ion in divalent form which gave emission bands peaking at 444 nm for the 320 nm excitation (solid-state lighting excitation), while for 254 nm it gave the same emission wavelength of low intensity (1.5 times) compared to 320 nm excitation. It was also observed that alkaline earth metal (Ca2+ and Sr2+) dopants increase the intensity of Eu2+ ion in BaAl12O19 lattice, thus this phosphor may be useful for solid-state lighting. 相似文献
19.
Positron annihilation lifetime (PAL) and Doppler broadening (DB) techniques have been performed to identify structural defects of the bismuth based pyrochlore systems with generic formula (Bi1.5Zn0.5)(Zn0.5−x/3TixNb1.5−2x/3)O7 (x = 0, 0.25, 0.5,1.0, 1.5). We found that all studied compounds contain substantial amount of the lattice vacancy defects, the variation of the annihilation lifetime suggests that the defects structure undergoes significant changes. The complex defects could be produced with increasing content of Ti, resulting in a drop in the intensity I2 in the Ti-rich sample. At 1 MHz their dielectric constant (?′) varies from 150 for Ti-poor system to 210 for Ti-rich system and loss tangent (tan δ) remains rather low level. The high dielectric constant response of the BZTN ceramics is attributed to loosening state of cations located in the center of octahedral, so favor off-center displacement. The occurrence of complex defects help to enhance the dielectric constant. 相似文献
20.
N. Ojha V.K. Malik C. Bernhard G.D. Varma 《Physica C: Superconductivity and its Applications》2009,469(14):846-851
Bulk polycrystalline samples of Eu2O3-doped MgB2 have been synthesized by a standard solid state reaction route and their structural and superconducting properties have been investigated. As a function of Eu2O3 content we have found a significant increase in the critical current density (Jc) and the irreversibility field (Hirr) in the magnetic field range 0–6 T. The XRD results reveal the presence of MgO and EuB6 secondary phases along with the main hexagonal phase of MgB2. The strain values and the lattice distortions have been found to increase almost linearly with the nominal Eu2O3 content. The observed significant improvement in Jc(H) and Hirr in the Eu2O3-doped MgB2 samples, thus is mainly attributed to the lattice distortions introduced by Eu2O3 doping. 相似文献