共查询到20条相似文献,搜索用时 31 毫秒
1.
Y. Xin B. R. Xu W. S. He G. F. Sun R. Farr D. F. Lu K. W. Wong D. Knapp 《Journal of Electronic Materials》1995,24(12):1821-1824
We have developed a technique to produce high quality Tl2Ba2Ca2Cu3O10 powders used for making superconducting wire, tape, lead, shield, and other large scale bulk applications. Starting with
T12O3, BaO2, CaO, and CuO, we mix and grind these chemicals with a machine ball mill and then press the ground mixture into pellets.
The pellets are sintered at about 895‡C for at least 30 h in an oxygen atmosphere. The sintered material is mainly the Tl2Ba2Ca2Cu3O10 compound. To get more homogeneous superconductor powders, we pulverize the sintered material and use a magnetic superconducting
material selector to separate and grade the material. Finally, the top grade material has a phase purity of <98% and a Tc(r < 0) of 123–126K. 相似文献
2.
L.P. Cook W. Wong-Ng P. Schenck Z. Yang I. Levin J. Frank 《Journal of Electronic Materials》2007,36(10):1293-1298
Interfacial reactions between the Ba2YCu3O6+x
superconductor and the CeO2 buffer layers employed in coated conductors have been modeled experimentally by investigating the kinetics of the reaction
between Ba2YCu3O6+x
films and CeO2 substrates. At 810°C, the Ba2YCu3O6+x
-CeO2 join within the BaO-Y2O3-CeO2-CuO
x
quaternary system is nonbinary, thereby establishing the phase diagram topology that governs the Ba2YCu3O6+x
/CeO2 reaction. At a mole ratio of Ba2YCu3O6+x
:CeO2 of 40:60, a phase boundary was found to separate two four-phase regions. On the Ba2YCu3O6+x
-rich side of the join, the four-phase region consists of Ba2YCu3O6 +x
, Ba(Ce1−z
Y
z
)O3−x
, BaY2CuO5, and CuO
x
; on the CeO2 rich side, the four phases were determined to be Ba(Ce1−z
Y
z
) O3−x
, BaY2CuO5, CuO
x
and CeO2. The Ba2YCu3O6+x
/CeO2 reaction is limited by solid-state diffusion, and the reaction kinetics obey the parabolic rule, x = Kt
1/2, where x = thickness of the reaction layer, t = time, and K = a constant related to the rate constant; K was determined to be 1.6 × 10−3 μm/s1/2 at 790°C and 4.7 × 10−3 μm/s1/2 at 830°C. The activation energy for the reaction was determined to be E
act = 2.67 × 105 J/mol using the Arrhenius equation. 相似文献
3.
Chakrapani Varanasi Paul J. Mc Ginn Howard A. Blackstead David B. Pulling 《Journal of Electronic Materials》1995,24(12):1949-1953
YBa2Cu3O7− δ (Y123) samples with excess Nd2O3 and Y2O3 additions in the same molar ratios were melt textured in air. In the Nd-doped samples, in addition to Y ion site substitution,
partial substitution into the Ba2+ sites is anticipated because of the similar ionic sizes of Nd3+ and Ba2+. The microstructure, Tc, and magnetic properties of Nd-doped samples were analyzed and compared with undoped Y123 and samples with excess Y2O3. The Nd2O3 additions lead to significant magnetization improvements, likely due to both rare earth- and Ba-site substitution by the
doped Nd3+ ions, and to increases in Tc. Y2O3 additions resulted in no marked property enhancement. 相似文献
4.
The phase transformation of Bi1.7Pb0.4Sr1.6Ca2.4Cu3.6Oy bulk materials rapidly melted and solidified by a CO2 laser with the scanning speed of 40 mm/s were investigated. Results of x-ray diffraction pattern, scanning electron microscopy
and energy-dispersive x-ray analysis showed the decomposition of the high-Tc phase in the laser irradiated region. Nonsuperconducting phases such as CaO and (Sr1−xCax)CuOy were found to be in the melting zone. On the other hand, (Sr1−xCax)CuOy and 2212 phase were also found in the heat-affected zone. When the irradiated samples were treated with 835‡C for 72 h in
air, the laser treated region changed into the high-Tc as a major phase, in addition to the low-Tc phase and nonsuperconducting phase. However, the high-Tc phases are piled up randomly. The transport critical-current density of the laser treated samples after annealing is lower
than that of the original sintered one, i.e. at 77K and zero magnetic field. 相似文献
5.
Rong Guo Siyu Duan Ze He Xuelian Liang Zihan Niu Ming He Yushun Jiang Jingbo Wu Lu Ji Biaobing Jin Jian Chen Huabing Wang Peiheng Wu 《Advanced functional materials》2021,31(52):2106891
The Josephson plasmon resonance (JPR) offers a valuable probe to investigate the superconductivity in layered cuprate superconductors. However, the coupling between free space radiation and JPR in high-temperature superconductor (HTS) film remains challenging because the excitation of JPR demands the c-axis oriented electric field. The subwavelength resonators in metamaterials can enhance the localized electric field, which can be utilized to resolve this difficulty. Here, a tunable terahertz (THz) metamaterial made from Tl2Ba2CaCu2O8 (Tl-2212) HTS film is developed. The spectral response of Tl-2212 metamaterial has a tunable property at temperatures up to 90 K. The resonant excitation of Josephson plasmon in the metamaterial is observed. Simulation results indicate that the scattering of subwavelength resonators can provide the component of the z-axis electric field for the resonant excitation. The coupling between JPR and resonance modes of metamaterials is observed and explained using coupled mode theory. The temperature dependence of JPR frequency shows accordance with the experimental results of the pure film. This work provides an avenue to excite the JPR and probe superconducting condensate in the layered superconductor. The development of Josephson plasmonic metamaterials may contribute to tunable and nonlinear THz devices. 相似文献
6.
E. Guerrero M. Quintero R. Tovar T. Tinoco J. González J. Woolley P. Conflant 《Journal of Electronic Materials》1993,22(3):297-301
The T(z) diagram of the system Cd1−zMnzGa2Se4 was obtained from x-ray diffraction and differential thermal analysis measurements. It was found that at lower temperatures,
a single phase solid solution occurs across the whole compositional range and values of lattice parameters were determined
as a function of z. At higher temperatures, an order-disorder transition occurs, in the range 0 < z < 0.6 to a partially ordered
tetragonal structure and for 0.6 < z < 1. 0 to a disordered defect zinc-blende structure. In the T(z) diagram, both the ordering
boundary and the solidus curve appear to show discontinuities at z = 0.6, corresponding to the change in the disordered phase.
It is suggested that the symmetries of the terminal compounds are different one from the other. Optical absorption measurements
were made at 300 K to show the variation of the direct optical energy gap Eo with z, and again the values appear to divide into two parts below the above z = 0.6. 相似文献
7.
V. Pavate L. B. Williams E. P. Kvam C. Varanasi P. J. Mc Ginn 《Journal of Electronic Materials》1994,23(11):1131-1134
Transmission electron microscopy examinations have been conducted on undoped and PtO2 doped YBa2Cu3O7−δ, with excess Y2BaCuO5 (211) in the molar ratio of 5∶1 (123/211), processing using the solid liquid melt growth technique. Magnetization hysteresis
suggests that addition of Pt strongly influences the pinning behavior. Considerable differences in dislocation and stacking
fault densities were observed. Dislocation nets and tangles were commonly observed in the Pt doped samples. In both samples,
stacking faults were observed near 211 precipitates, interplatelet boundaries, and dislocations. Dislocations appear to be
formed during high temperature processing, while stacking faults appear to be generated during the final oxygenation step.
The density and distribution of fine precipitates (∼25–100 nm) were comparable in both specimens suggesting that Pt additon
affects the size and acicular morphology of only the coarser 211 (∼1–10 μm). It is proposed that the observed increase in
Jc due to Pt addtion may be attributed to the increase in defect density rather than fine precipitates. 相似文献
8.
Rare-earth-modified ferroelectric crystals with the formula (Sr1−xBax)1− 3y/2 RyNb22O6, where R = La, Nd, Sm, Gd, and Lu, have Been prepared and studied. When R = La, Nd, x ≃ .5 and y = 0.02, the modified material,
at room temperature, exhibited twice the pyroelectric coefficient and four times the dielectric constant of the unmodified
Sr1−xBaxNb2O6 (x ≃ .5). Curie temperatures decreased, dielectric constants increased, while loss factor and detector signal-to-noise ratios
remained nearly the same with the addition of rare earth doping. The calculated response based on the measured properties
agree with the measured response of actual detectors. These properties suggested that the modified SBN are good materials
for small element or array pyroelectric infrared detector applications. 相似文献
9.
Khier Benmahammed Abdelaziz Hamzaoui Najib Essounbouli 《Multidimensional Systems and Signal Processing》2006,17(1):75-87
In this paper, results of the one-dimensional (1D) digital filtering are extended to the two-dimensional (2D) case. It introduces
a technique and an algorithm for the computation of the product H(z1,z2)H(z1−1,z2−1). The technique is used to find a minimum phase transfer function of a 2D system such that the previous product matches a
given correlation sequence. The algorithm requires less arithmetic operations than the traditional methods. The former is
based on a matrix formulation of the product, which is used to investigate the 2D partial fraction decomposition (PFD) and
stability. 相似文献
10.
Mg2Sn compounds were prepared by the modified vertical Bridgman method, and were doped with Bi and Ag to obtain n- and p-type materials, respectively. Excess Mg was also added to some of the ingots to compensate for the loss of Mg during the
preparation process. The Mg2Sn samples were characterized by x-ray diffraction (XRD) and scanning electron microscopy (SEM), and their power factors were
calculated from the Seebeck coefficient and electrical conductivity, measured from 80 K to 700 K. The sample prepared with
4% excess Mg, which contains a small amount of Mg2Sn + Mg eutectic phase, had the highest power factor of 12 × 10−3 W m−1 K−2 at 115 K, while the sample doped with 2% Ag, in which a small amount of eutectics also exists, has a power factor of 4 × 10−3 W m−1 K−2 at 420 K. 相似文献
11.
Ali Saramat Eric S. Toberer Andrew F. May G. Jeffery Snyder 《Journal of Electronic Materials》2009,38(7):1423-1426
Polycrystalline Ba8Ga
x
Ge46−x
exhibits promising thermoelectric performance with the figure of merit ZT close to that of single crystals. Polycrystalline Ba8Ga
x
Ge46−x
is promising for applications, but reproducibility and thermal stability of thermoelectric properties need to be demonstrated.
Polycrystalline samples of Ba8+dGa
x
Ge46−x
-type clathrates (15.0 ≤ x ≤ 16.8 with varied nominal Ga content and d = 0 or 0.2) were prepared by direct reaction of the elements, followed by ball milling and hot pressing. Trace Ge impurity
was observed (<1.0 wt.%) depending on the synthesis method. The electrical resistivity was stable in measurements up to 1000 K,
regardless of Ge impurity. However, measurements to 1050 K resulted in irreversible increase in carrier concentration while
the carrier mobility remained unchanged. 相似文献
12.
We performed thermoelectric characterizations on TlCu3Te2: (Tl1+)(Cu1+)3 (Te2−)2 and TlCu2Te2: (Tl1+)(Tl3+)(Cu1+)4(Te2−)4, in order to understand the relationship between the thermoelectric properties (especially the lattice thermal conductivity
κ
lat) and the valence states of Tl. The thermal conductivity of TlCu2Te2 is high (about 8 W m−1 K−1), while that of TlCu3Te2 is extremely low (around 0.5 W m−1 K−1) like other thallium tellurides. This high κ of TlCu2Te2 was caused not only by its large electronic contribution but also by its intrinsically high κ
lat. The present study implies that the valence states of Tl would play some important roles in determining the magnitude of
κ
lat. 相似文献
13.
Practical superconducting thick films and tapes, manufactured in an industrial process, have microscopic inhomogeneities.
Quantitative magneto-optical imaging (MOI) is one of the most desirable techniques and provides both local and global information
on defects, flux pinning, critical current density J
c, and current distribution. We present, herein, a comparative magneto-optical imaging study of the flux profile in YBa2Cu3O7−δ (YBCO) thick films prepared in two different processes, the laboratory versus the industrial scalable process. The remarkably
different flux propagation patterns are the manifestation of their different defect landscapes within these films. A method
of determining J
c near zero applied field is also given for locally nonuniform superconducting films, using the quantitative MOI technique. 相似文献
14.
M. J. Kramer A. Karion K. W. Dennis M. Park R. W. McCallum 《Journal of Electronic Materials》1994,23(11):1117-1120
Previous work has shown that unlike YBa2 Cu3 O7-δ (Y123), the Nd-Ba-Cu-O system exhibits a solid solution Nd1+xBa2-x Cu3O7+δ (Nd123ss) for 0.04≤ × ≤0.6.1–3) An earlier paper showed that although the superconducting properties decrease nonlinearly for increasing x, Tc can be varied by increasing the annealing temperature without changing the low temperature oxygen soak.2 The changes in microstructure and Tc with increasing x are analogous with Y123 with increasing δ except that the total hole concentration remained constant. Tc was modeled in terms of oxygen disorder resulting from Nd3+ atoms on the Ba sites relocating chain oxygens to anti-chain sites. The variability in Tc as a function of x and processing conditions can be explained by the number of fourfold coordinated coppers on the chain
sites. In this paper, the model has been further substantiated by processing in 1% O2. The annealing in a reduced oxygen partial pressure followed by a 450°C oxygen soak resulted in a marked increase in Tc compared to the 100% PO2 anneal. The low PO2 anneal favors pairing of Nd3+ substituting for Ba2+ to conserve oxygen ions, resulting in fewer disrupted fourfold-coordinated coppers thus increasing charge transfer from the
planes to the chains. 相似文献
15.
Superconducting Properties of (M
x
/YBa2Cu3O7−δy
)N Multilayer Films with Variable Layer Thickness x
T.J. Haugan P.N. Barnes T.A. Campbell N.A. Pierce F.J. Baca M.F. Locke I. Brockman A.L. Westerfield J.M. Evans R. Morgan P. Klenk B.C. Harrison A.D. Chaney I. Maartense 《Journal of Electronic Materials》2007,36(10):1234-1242
The superconducting properties of (M
x
/YBa2Cu3O7−δy
)N multilayer films were studied for varying layer thickness x. Different M phases were examined including green-phase Y2BaCuO5 (211), Y2O3, BaZrO3, CeO2, SmBa2Cu3O7−δ (Sm123), brown-phase La2BaCuO5 (La211), and MgO. Multilayer (M
x
/YBa2 Cu3O7−δy
)N structures were grown by pulsed laser deposition onto SrTiO3 or LaAlO3 single-crystal substrates by alternate ablation of separate YBa2Cu3O7−δ (123) and M targets, at temperatures of 750°C to 790°C. The x layer thickness was varied from 0.1 nm to 4.5 nm, and the y 123 layer thickness was kept constant within a given range of 10 to 25 nm. Different M phase and x layer thicknesses caused large variations of the microstructural and superconducting properties, including superconducting
transition (T
c), critical current density as a function of applied magnetic field J
c(H), self-field J
c(77 K), and nanoparticle layer coverage. Strong flux-pinning enhancement up to 1 to 3x was observed to occur for M additions of 211 and BaZrO3 at 65 to 77 K, Y2O3 at 65 K, and CeO2 for H < 0.5 T. BaZrO3 had a noticeably different epitaxy forming smaller size nanoparticles ∼8 nm with 3 to 4x higher areal surface particle densities than other M phases, reaching 5 × 1011 nanoparticles cm−2. To optimize flux pinning and J
c (65 to 77 K, H = 2 to 3 T), the M layer thickness had to be reduced below a critical value that correlated with a nanoparticle surface coverage
<15% by area. Unusual effects were observed for poor pinning materials including Sm123 and La211, where properties such as
self-field J
c unexpectedly increased with increasing x layer thickness. 相似文献
16.
V. R. Todt S. Sengupta Donglu Shi P. R. Sahm P. J. McGinn R. B. Poeppel J. R. Hull 《Journal of Electronic Materials》1994,23(11):1127-1130
YBa2Cu3Ox domains for levitation applications have been produced by a seeding technology that includes Nd1+x Ba2−x Cu3Oy seeds and melt-processing technologies such as conventional melt-textured growth, melt-texturing with PtO2 and Y2BaCuO5 additions, and the new solid-liquid-melt-growth technology. Large domains (∼20 mm) with high levitation forces (F1 up to 8.2 N) have been produced. The reproducibility of the results is good, and the capability of producing a large number
of pellets in a single batch indicates good potential for the production of large amounts of this material. 相似文献
17.
S.H. Wee A. Goyal J. Li Y. Zhang L. Heatherly 《Journal of Electronic Materials》2007,36(10):1230-1233
NdBa2Cu3O7−δ (NdBCO) films were grown on rolling-assisted biaxially textured substrates (RABiTS) via pulsed laser deposition. c-Axis-oriented epitaxial NdBCO films with high performance were obtained under optimal deposition conditions. Transmission
electron microscopy analysis shows that the NdBCO film grown on RABiTS has a clear interface with a CeO2 cap layer and a nearly perfect lattice structure. The NdBCO film exhibits higher T
c of 93.7 K and better in-field J
c in magnetic fields and at all field orientations, compared to pure YBCO films. 相似文献
18.
G. A. Bordovsky A. V. Marchenko E. I. Terukov P. P. Seregin T. V. Likhodeeva 《Semiconductors》2008,42(11):1323-1326
Tin is stabilized in the bivalent and tetravalent states in the structure of (As2Se3)1 − z
(SnSe2)
z − x
(Tl2Se)
x
and (As2Se3)1 − z
(SnSe)
z − x
(Tl2Se)
x
glasses. The presence of bivalent tin in the structural network of a glass does not give rise to extrinsic conductivity.
Dependences of density, microhardness, and the glass-transition temperature on the composition of the glasses are interpreted
using a model according to which the structure of the glasses is composed of structural units that correspond to As2Se3, AsSe, TlAsSe2, Tl2Se, SnSe, and SnSe2 compounds.
Original Russian Text ? G.A. Bordovsky, A.V. Marchenko, E I. Terukov, P.P. Seregin, T.V. Likhodeeva, 2008, published in Fizika
i Tekhnika Poluprovodnikov, 2008, Vol. 42, No. 11, pp. 1353–1356. 相似文献
19.
K. C. Goretta V. R. Todt D. J. Miller M. T. Lanagan Y. L. Chen U. Balachandran J. Guo J. A. Lewis 《Journal of Electronic Materials》1995,24(12):1961-1966
Three methods were used to introduce flux-pinning centers into Bi2Sr2CaCu2Ox (Bi-2212) and TlBa2Ca2Cu3Ox (Tl-1223) samples. It was found that carbon induced local decomposition, that nanosized Al2O3 additions created stable reaction products, and that second phases could be isolated in Tl-1223 during synthesis. Each of
these defects enhanced flux pinning and was of most benefit at temperatures ≤ 35K. 相似文献
20.
Ohmic contacts have been fabricated on p-type 6H-SiC (1.3×1019 cm−3) using CrB2, W2B, and TiB2. The boride layers (∼100–200 nm) were sputter-deposited in a system with a base pressure of 3×10−7 Torr. Specific contact resistances were measured using the linear transmission line method, and the physical properties of
the contacts were examined using Rutherford backscattering spectrometry. All as-deposited contacts exhibited rectifying characteristics.
Ohmic behavior was observed following short anneals (2–10 min) at 1100°C and 5×10−7 Torr. Current-voltage characteristics were linear for CrB2 and W2B and quasi-linear for TiB2. The lowest values of the specific contact resistance (rc in Ω-cm2) measured at room temperature for CrB2 and W2B were 8.2×10−5 and 5.8×10−5, respectively. The specific contact resistance for TiB2 was not determined accurately. Longer anneals (30 min for W2B and 90 min for CrB2) reduced the room temperature values of rc to 6.1×10−5 for W2B and 1.9×10−5 for CrB2. Backscattering spectra revealed substantial concentrations of oxygen in all as-deposited boride films. The short anneal
cycle removed the oxygen in the CrB2 films and reduced the concentration substantially in the W2B films; however, annealing had no affect on the oxygen concentration in the TiB2 films. The CrB2/SiC interface remained stable during annealing; i.e., Si and carbon were not observed in the boride layers after annealing.
In contrast, W2B and TiB2 reacted with the SiC epilayers, and after annealing, Si and carbon were observed at the surface of each boride layer. 相似文献