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1.
M. Hagiwara T. Shima R. Kitada H. Deguchi K. Koyama 《Physica C: Superconductivity and its Applications》2010,470(20):1052-1055
Intergrain ordering phenomena of frustrated ceramic YBa2Cu4O8 (Y124) and dual phase mixed ceramic containing CuO are studied by both magnetic and resistivity observations. Magnetically estimated intergrain ordering temperature Tc2 and zero-resistivity attainment temperature Tz are both decreased with CuO content. However, it is also revealed that mutual location of Tc2 and Tz is changed. For the mixed ceramic with torn intergrain network structure, Tz stays above Tc2, indicating local dissolution of frustration by cluster structure. On the other side, remaining resistivity tails blow Tc2, indicating intrinsic fluctuation effect on the resistivity caused by frustration in the ordered state. It is known then that, superconductive ceramic samples which is free from structural phase inhomogeneity is essential in order to clarify the frustration effect. 相似文献
2.
Plasma-enhanced MOCVD in which metal-organic compounds are sublimated directly into the growth chamber is studied for the first time as a new low-temperature process for growing superconducting YBa2Cu3O--x thin films. Y(THD)3, Ba(THD)2, Cu(THD)2 and oxygen are used as metal sources and oxydizing agent. Emission spectroscopy reveals that activated metal-organic compounds and activated oxygen species are present during film growth. Superconducting YBa2Cu3O7-x films whose zero-resistivity temperature are 50 K and 82 K are grown at 550°C and 600°C. 相似文献
3.
The oxide responsible for high-temperature superconductivity (onset ∼100 K, zero resistance above liquid N2 temperature) is found to be YBa2Cu3O7±δ.
Contribution No. 432 from the Solid State and Structural Chemistry Unit 相似文献
4.
S. L. Chaplot 《Phase Transitions》2013,86(1-3):49-59
Molecular-dynamics simulation of YBa2Cu3O7 is carried out to study the oxygen-atom distribution at high temperatures as the system undergoes the orthorhombic-to-tetragonal phase transition. While at the transition the one-dimensional arrangement of oxygen atoms in the Cul(0,0,0)-O4(0, 1/2, 0) chains begins to disorder, at temperatures above the transition the simulation also indicates the presence of a few vacancies at the O1(0, 0, z) sites. At still higher temperatures vacancies occur at all the oxygen sites. The simulation utilises an interatomic potential based on an unscreened rigid-ion model which was earlier found to be useful in understanding the structure, phonon density of states, and related properties. The thermal expansion, as obtained from the zero-pressure simulation, is in reasonable agreement with the observations of Jorgensen et al. on the oxygen-deficient system. The melting temperature obtained from the simulation is also in fair agreement with experiment. 相似文献
5.
We have used x-ray photoelectron spectroscopy to investigate the charge state of oxygen found in the basal structural plane
of YBa2Cu3O6+γ.. We have observed a change in this state after thermal treatment, with a transition to the adjacent structural phase region.
We have shown that changes in the charge state of oxygen can be used as an indicator of structural changes occurring in YBa2Cu3O6+δ.. We have found that the rate of structural relaxation yttrium barium cuprate depends on the amount of structural water
it contains.
__________
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 2, pp. 195–198, March–April, 2007. 相似文献
6.
Dhananjai Pandey V. S. Tiwari A. K. Singh V. K. Wadhawan M. S. Somayazulu 《Phase Transitions》2013,86(2-3):165-202
Crystal structures and structural inhomogeneities observed in YBa2Cu3O7-y are reviewed. It is brought out that a proper understanding of the nature of the structural inhomogeneities is essential for exploiting the technological potential of this material. The need for an adequate characterization of specimens used for experiments is emphasized. Practical implications of the ferroelastic nature of the material are discussed. 相似文献
7.
The fine structure of YBaCu3O7 is examined: Twin organization, planar defects, and structural phase co-existence are discussed in the context of the tetragonal to orthorhombic transformation. Heterogeneous nucleation of an insulating phase at the twin boundary and sub-grain boundaries is demonstrated. On the basis of the morphological observations, the transformation is classified as martensitic. Considering the role of twin in relieving the martensitic transformation strain, by producing a low strain energy habit plane, the feasibility of the formation of a twinless structure is discussed. 相似文献
8.
Abstract It is shown that heavy atom disorder resulting from Y ? Ba, Ba ? Cu and Y ? Cu interchanges due to local stoichiometric constraints can cause significant changes in the intensities of X-ray powder diffraction lines of YBa2Cu3O7-y . A comparison of the theoretically predicted intensities with published patterns for specimens prepared by the conventional dry route reveals that Ba ? Cu interchanges involving copper atoms in the CuO2 planes can occur quite frequently and may be mistaken for (00l) texture. 相似文献
9.
Besides ag ≈ 2 signal which disappears on cooling to the superconductingT
c
, YBa2Cu3O7 and related oxides show a near-zero-field signal in the superconducting state with certain unusual features attributable
to a “superconducting glassy state”.
Contribution No. 443 from Solid State and Structural Chemistry Unit. 相似文献
10.
Tadashi Kobayashi Hiratoshi Katsuda Yukio Sakabe Kiyoshi Iwai Seiji Kanba 《Phase Transitions》2013,86(3):215-223
EPR spectra of superconducting YBa2Cu3O7-δ and insulating Y2BaCuO5 have been examined. The intensity of Cu2+ ions in YBa2Cu3O7-δ is about 1/3000 of that in Y2BaCuO5 at room temperature. Owing to the Meissner effect in the superconducting state, the EPR signal of Cu2+ ions in YBa2Cu3O7-δ disappears; moreover the EPR signal of DPPH deposited on the YBa2Cu3O7-δ specimen is shifted. An additional EPR line is found for YBa2(Cu2.94Cr0.06)O7-δ at temperatures below 113K; this can be related to the phenomenon of superconductivity. 相似文献
11.
利用正电子湮没技术,结合X射线衍射和扫描电子显微镜结构分析,对Y-123超导体烧结过程进行了研究,给出了烧结时间、烧结温度对该体系结晶度和晶体结构的影响特征,发现在950℃温度烧结下,随烧结时间的增加,Y-123体系的正交畸变度增加;而就整体而言,正电子平均寿命随烧结温度和烧结时间增加而增加,并趋于饱和.证明在烧结温度为920—950℃、烧结时间为12—72h的实验条件下,Y-123超导材料中的缺陷分布趋于稳定.讨论了烧结过程中材料内部的缺陷变化特征
关键词:
正电子寿命谱
2Cu3O7-δ超导体')" href="#">YBa2Cu3O7-δ超导体
烧结过程
晶体结构 相似文献
12.
Investigations of oxide superconductors by x-ray absorption,photoemission and cognate spectroscopies
X-ray absorption spectra, X-ray photoelectron spectra and Auger spectra of cuprate superconductors are discussed. The studies establish the absence of Cu3+ for all practical purposes, but point out the importance of oxygen holes. X-ray photoelectron spectra of BaBi0.25Pb0.75O3 and related compounds are also examined. 相似文献
13.
R. Teranishi Y. Miyanaga K. Yamada N. Mori M. Mukaida M. Miura M. Yoshizumi T. Izumi M. Namba S. Awaji K. Watanabe 《Physica C: Superconductivity and its Applications》2010,470(20):1246-1248
Tin-compounds were doped into YBa2Cu3O7−δ (YBCO) films as pinning centers to enhance Jc in magnetic fields. YBCO films were grown by a metal organic deposition process using tri-fluoroacetates starting solutions. Tin-acetylacetonate salts were then dissolved into the starting solution as pinning centers. Jc of the YBCO films with tin-acetylacetonates were enhanced in all magnetic field angles. Transmission electron microscopy (TEM) and TEM-EDS (Energy Dispersive X-ray Spectroscopy) observations revealed the existence of tin-compound particles with the size of about 30 nm in the YBCO film. These nano particles were distributed randomly in the film and were considered to act as 3-dimentional pinning centers. 相似文献
14.
Abstract X-ray powder diffraction measurements for YBa2Cu3O7-y and NdBa2Cu3O7-y were made at the intense synchrotron radiation source under high pressure up to 5 GPa. These samples were wrapped tightly in platinum foil to avoid deoxidizing atmosphere. The orthorhombic to tetragonal transition temperature increases with pressure in both samples. These results are discussed on the basis of the disordering of the oxygen atoms on the chain sites. 相似文献
15.
S. Mazumder H. Rajagopal A. Sequeira Jagriti Singh A. K. Rajarajan L. C. Gupta 《Phase Transitions》2013,86(1-3):97-105
Effects of doping YBa2Cu3O7-δ with Mg and Zn on its crystallographic structure and superconducting behaviour have been investigated. Orthorhombic structure is retained upto Mg/Cu ratio of 0.12 (the highest investigated here), but Tc decreases rapidly with the level of Mg-doping. The effects produced by Mg-doping are very similar to those due to Zn-doping investigated by the present authors as well as by others. Neutron diffraction measurements have been carried out on two substituted materials: YBa2Cu2.82Mg0.18O7-δ and YBa2Cu2.82Zn0.18O7-δ. Both Mg- and Zn-dopants show strong tendency of occupying Cu(II)-sites in the unit cell. In the case of Mg-doping, however, a strikingly different feature is the concomitant depletion of oxygen at the O3-sites by an amount nearly equal to the Mg-concentration. 相似文献
16.
A “grain coating” technique was developed to improve the intergranular links in YBa2Cu3O x ceramics. Thin layers of additives such as Ag, SnO2, Bi2O3 were introduced into the grain boundaries by vacuum evaporation. Notable Jc increments due to grain coating were observed. TEM investigation revealed that dislocations accompanied by stacking faults existed in these samples. 相似文献
17.
Abstract The FIR transmission of an YBa2Cu3O7-δ film 1000 Å thick deposited on an MgO plate has been studied from 20 cm?1 to 4000 cm?1 at T = 300 K, and at 120 K, 80 K and 7 K. i) The spectra for the normal state are well fitted if a mid-IR oscillator of high strength and high damping is added to the simplest Drude model. ii) The spectra for the superconductive state do not show significant variations of transmission vs. temperature for ω > 120 cm?1, which should be in agreement with a weak BCS coupling 2Δ = 3.5 kTc . iii) The FIR transmission at 7 K for ω = 20 cm?1 is not zero (around 1%) and seems to confirm that the low-temperature perovskite is made of two phases: a superconducting, and a normal one, the proportion of the first one increasing when the film temperature is decreased. 相似文献
18.
Mössbauer study of orthorhombic and tetragonal YBa2(Cu1-xFex)3O7-σ;x=0.02, 0.04, 0.08 has been done to investigate the two inequivalent Cu-sites. Fe substituting Cu having pyramidal oxygen co-ordination is in Fe3+ state while Fe substituting Cu having square planar co-ordination is in Fe3+ and Fe4+ states in dynamic equilibrium. 相似文献
19.
Hiroshi Yasuoka Susumu Sasaki Takashi Imai Tadashi Shimizu Yutaka Ueda Koji Kosuge 《Phase Transitions》2013,86(4):183-199
The nuclear quadrupole resonance (NQR) technique has been utilized to characterize the local oxygen coordination of inequivalent Cu sites in YBa2Cu3O6+x(0 ≤ x ≤ 0.91). Essentially, four distinct NQR lines which correspond to 2, 3,4 oxygen coordinated Cu sites in the Cu-O chains and 5 oxygen coordinated Cu sites in the Cu-O planes have been observed. The zero-field NQR frequencies of these are centered at about 30.1, 24.0, 22.0 and 31.5 MHz for 63Cu, respectively. For the antiferromagnetic ordered state (x ≤ 0.3), antiferromagnetic nuclear resonance (AFNR) has been observed at 90 MHz with quadrupole splittings associated with the moment-bearing Cu sites in the Cu-O planes. The relative intensities of these resonance lines depend on the oxygen content, and this gives us a microscopic understanding of the Cu chemistry of this system. 相似文献
20.
Sangeeta 《Journal of luminescence》2003,104(4):267-271
The thermally stimulated luminescence from XB2O4 (X=Ca,Sr,Ba) has been investigated. The results on CaB2O4 and SrB2O4 are being reported here for the first time. In both cases, the emission is found to be quite intense, contrary to the case with BaB2O4. The presence of two peaks in the glow curves is noted over the temperature range of 300-570 K. The emission spectra corresponding to both the peaks have been observed to be identical, consisting of two broad emissions, one in the UV and other in the blue-green regions. The emission is apparently quite different from that of BaB2O4 in which case only very weak emission spreading over a broad wavelength range around 410 nm is observed. This result has been understood in terms of the overlap between the excitation and the emission spectra. 相似文献