high-Tc Superconductor YBa2Cu3O7 Research Articles

Mössbauer effect of tin-119 doped in highT c Y−Ba−Cu−O superconductor

Mossbauer measurements at temperatures ranging from 12 K to 300 K have been carried out on highTc superconductor YBa2Cu3O6+δ samples doped with Sn (5,2 and 0.5 wt%). The temperature dependent recoilless fractionf(T) has a narrow and small drop nearby transition temperatureTc which is dependent on the Sn-concentration and has a drop between 200–220 K. This indicates the occurrence of phonon softening at these temperatures. The Debye temperature θD of the samples containing 5, 2 wt% Sn atoms was determined as (290±25) K and (320±13) K respectively. These results show that phonons may play an important role for electron pairing in novel oxide superconductor.

Twinning in ferroelectric and ferroelastic ceramics: stress relief

The regular twinning in ceramics and metals below the temperature of a ferroelastic or ferroelectric structural phase transition is a result of energy minimization. Here homogeneous elastic energy is reduced at the expense of twin wall energy. The twin density depends on the gram sizeg; under homogeneous stress the total elastic energy of a grain increases ∝g 3. Any kind of twin wall, however, increases ∝g 2. Below the intersection of these two curves, stress reduction by twinning cannot lower the total energy. Thus there is a critical grain size below which twinning should not occur. Above this limit the width of the twin lamellae increases ∝g 1/2. The shape of the grain then adjusts to the surroundings in two dimensions only. Above another larger critical grain size more complex interfaces with higher surface energy are created, which allow stress relief in the third dimension. A semi-quantitative model is developed with the example of BaTiO3 ceramic, of which the domain patterns are well known. It is representative for many ceramics. The highT c superconductor YBa2Cu3O7−δ also twins according to the same law. For three-dimensional adjustment here a proper interface is missing.

Theory of internal friction in the high-Tc superconductor YBa2Cu3O7-δ

The internal friction in the high-Tc superconductor YBa2Cu3O7- delta arising from the diffusion of oxygen atoms between the O(1) and O(5) sites under the influence of a periodic mechanical strain is studied microscopically in the linear approximation of the relaxation process. It is analysed for various specific cases in both the tetragonal and the orthorhombic phases as well as in the case of polycrystalline samples.

Electronic Structure of the High-Tc Superconductor YBa2Cu3O7: A detailed description

We present results from a calculation of the electronic structure of the high-Tc superconductor YBa2Cu3O7. In the calculations fully self-consistent standard LMTO method was used in the atomic sphere approximation in connection with the density functional theory. We give a detailed description of the electronic structure of the compound in terms of energy bands, state densities, charge densities and potential parameters. We also give parameters for a simple tight-binding type model based on our first principles band structure.

Valency and covalency in high-Tc-superconductors from x-ray absorption

The local electronic structure of the high-Tc superconductors YBa2Cu3O7−δ and Nd2−xCexCuO4−δ is probed by soft x-ray absorption spectroscopy at the CuLII,III, OK, CeMIV,V, and NdMIV,V thresholds. The near-edge structures provide information on the partial unoccupied density of states above EF as well as on valency and covalency of the constituent elements.

Effect of Oxygen Loss on Densification When Hot Isostatic Pressing YBa2Cu3O7−δ

Hot isostatic pressing of the high‐Tc superconductor YBa2Cu3O7−δ can lead to loss of oxygen and transformation of the material from the high‐Tc orthorhombic phase to the nonsuperconducting tetragonal phase. It is shown that glass encapsulation helps retain the orthorhombic structure, whereas steel encapsulation resulted in formation of the tetragonal phase. Reasons for this phenomenon are discussed. The equilibrium oxygen gas pressure for the oxygen decomposition reaction in YBa2Cu3O7, however, prevents full densification of this material in glass when employing hot isostatic pressing conditions of 200 MPa and 845°C.

A new look at the structure of the high-TC superconductor YBa2Cu3O7−δ

In this communication we show how the structure of orthorhombic YBa 2 Cu 3 O 7−δ can be described as a commensurately modulated structure. The symmetry is characterized by the superspace group P Pmmm 111 (0,0,γ), γ = 1 3 . While retaining the centrosymmetric superspace group symmetry, a possible reduction from Pmmm to Pmm2 symmetry is found, which was not considered previously. The importance of this superspace group analysis for the tetragonal phase and incommensurate YBa 2 Cu 3 O 7−δ phases is discussed briefly.

Positron annihilation anomaly in the high-temperature superconductor YBa2Cu3O7−x

Positron annihilation measurements in the highT c superconductors YBa2Cu3O7−x have been performed. The Doppler broaded annihilation line has been used for determination of theS parameter as a function of temperature between 13 and 100 K. Measurements from 80 to 100 K were performed at close temperature intervals and showed a resonance like change inS in a narrow temperature range near the transition temperatureT c .Such behaviour ofS can be linked to an anomalous change in the lattice parameterc. The second decrease of theS parameter was observed below 30 K.

Ac susceptibility in ceramic and powdered YBa2Cu3O7–δ

The complex susceptibility of high Tc superconductor YBa2Cu3O7–δ is measured as a function of temperature, for different values of ac field amplitude and dc field. The measurements are carried out on ceramic and powdered samples. Moreover, the dependences of lower critical fields upon the temperature measured by the dc susceptometer are presented. It is concluded that the best description of experimental data gives the weak link model, which also predicts a spin glass like behaviour. [Russian Text Ignore]

Nature of contact resistance in high-T c YBa2Cu3O7?? Superconductors

The contacts between various metals and the high-Tc superconductor YBa2Cu3O7−δ are characterized by contact resistance,Rc, andI–V measurements from 300 K to 90 K. The contacts with bulk superconductor were made by vacuum deposition. Four metals, Au, Ag, Al, and Bi were investigated. The current transport across the contact is by carrier tunneling. All contacts were ohmic as theirI–V characteristics were symmetrical with respect to current direction.Rc values range between 10−2 to 101 Ωcm2 and increase linearly as the temperature is lowered. The contact resistance originates from two distinct physical processes. One is the modification of the carrier concentration at the interface by the contact metal. The second is the nature of carrier injection at the free surface of the superconductor. TheRc values depend on the contact metal-oxygen interaction parameter signifying the need for oxygen passivation for obtaining low contact resistances.

ChemInform Abstract: Magnetic and Electrical Properties of High‐Tc Superconductor YBa2Cu3O6.87.

ChemInformVolume 20, Issue 12 Physical Inorganic Chemistry ChemInform Abstract: Magnetic and Electrical Properties of High-Tc Superconductor YBa2Cu3O6.87. D. KIM, D. KIM Dep. Chem., Yonsei Univ., Seoul 120-749Search for more papers by this authorC. K. KANG, C. K. KANG Dep. Chem., Yonsei Univ., Seoul 120-749Search for more papers by this authorK. H. KIM, K. H. KIM Dep. Chem., Yonsei Univ., Seoul 120-749Search for more papers by this authorJ. S. CHOI, J. S. CHOI Dep. Chem., Yonsei Univ., Seoul 120-749Search for more papers by this author D. KIM, D. KIM Dep. Chem., Yonsei Univ., Seoul 120-749Search for more papers by this authorC. K. KANG, C. K. KANG Dep. Chem., Yonsei Univ., Seoul 120-749Search for more papers by this authorK. H. KIM, K. H. KIM Dep. Chem., Yonsei Univ., Seoul 120-749Search for more papers by this authorJ. S. CHOI, J. S. CHOI Dep. Chem., Yonsei Univ., Seoul 120-749Search for more papers by this author First published: March 21, 1989 https://doi.org/10.1002/chin.198912020Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume20, Issue12March 21, 1989 RelatedInformation

A comparative study of the electronic structures of the high-Tc superconductors YBa2Cu3O7 and Bi2Sr2CaCu2O8

Results of the electronic structure calculations for the compound Bi2Sr2CaCu2O8 are discussed and compared to those obtained for YBa2Cu3O7. An analysis of the contribution of the densities of states at different atomic sites shows that the states at the Fermi energy, EF, have a strong two-dimensional character due to the presence of the CuO2 planes. Moreover, for the bismuth compound, the contribution of the Bi-O planes at EF is substantial. The elements Y and Ba in YBa2Cu3O7 and Ca and Sr in Bi2Sr2CaCu2O8 act essentially as electron donors, and their corresponding densities of states at EF are negligible. An analysis of the electronic charges at different atomic sites shows that the CuO3 chain units in YBa2Cu3O7 and the BiO2 plane units in Bi2Sr2CaCu2O8 play the role of electron reservoirs for the creation of holes in the CuO2 planes.

Spectral characteristics of plasma emission during ArF excimer laser ablation of YBa2Cu3O7

In order to characterize the laser ablation process as it relates to the deposition of high Tc superconducting thin films, optical emission spectra produced during ArF excimer laser ablation of the high Tc superconductor YBa2Cu3O7 were studied. The population of excited states within the gas phase blow-off material depends strongly on excimer laser fluence at 193 nm. Ablation using relatively low excimer laser fluences produces a significant fraction of YO in the gas phase. The plasmas derived from ablation of targets made from the high Tc material are similar to plasmas observed from ablation of the individual components BaCO3, CuO, and Y2O3.

High Resolution Stem Images and Nanodiffraction Patterns on High Tc Superconductor YBa2Cu3O7−x

High resolution scanning transmission electron microscopy (HRSTEM) and the nanodiffraction patterns of the high T c superconductor of Yba 2 Cu 3 O 7−x were studied with the use of a dedicated VG-HB5 STEM microscope. STEM imaging on the YBa 2 Cu 3 O 7−x [100] shows atomic resolution image of the heavy atoms. Approximately 750 diffiaction patterns were recorded with the nano-probe electron beam of 3A in diameter scanned over a region of 20A×12A on the specimen. Simulation of the diffraction patterns is employed to recognize the patterns for beams centered on Cu(1), O(4), Ba and Y. The local symmelry around an individual atom can then be studied. STEM images of the Yba 2 Cu 3 O 7−x [001] show the edge dislocations temlinating at the grain boundary and the microdiffraction patterns show the 2-fold symmetry for the core of the dislocation and the (110) plane symmetry for the grain boundary.

Organometallic chemical vapor deposition of high T c superconducting films using a volatile, fluorocarbon-based precursor

Uniform films of the high Tc superconductor YBa2Cu3O7−δ have been prepared by organometallic chemical vapor deposition using the volatile metalorganic precursors Cu(acetylacetonate)2, Y(dipivaloylmethanate)3, and Ba(heptafluorodimethyloctanedionate)2. With argon as a carrier gas and water vapor as a reactant, film growth rates of 10–30 nm/min are achieved. After annealing under oxygen, energy dispersive x-ray analysis, profilometry, and x-ray diffraction data reveal that such YBa2Cu3O7−δ films on [100] single-crystal MgO have good compositional and dimensional uniformity as well as preferential orientation of crystallite c axes perpendicular to the substrate surface. Four-probe resistivity measurements reveal the onset of superconductivity at ∼90 K and zero resistance by 66.2 K.

Critical and supercritical current measurements by a magnetic induction method

Abstract The temperature dependence of the critical current and current-voltage characteristics at supercritical currents have been measured in the low field limit on toroidal samples of the ceramic high Tc superconductor YBa2Cu3O7−δ by a contactless magnetic induction technique that is sensitive to the transport supercurrent but not to any intragrain current loops. The sample constitutes a tertiary winding on a small ferrite transformer core. The secondary voltage provides a very sensitive indication of when the critical current is exceeded, and when it is integrated it yields the supercritical current-voltage characteristic.

Superconductivity classes in YBa2Cu3O7 and the orthorhombic distortion anomaly

The symmetry classification of the possible superconducting states is made for the high-Tc superconductor YBa2Cu3O7 in assumption that the superconductivity is generated in the nearly tetragonal background of the layers of fivefold-coordinated Cu atoms and that the orthorhombic distortion may be considered as a perturbation. The interaction of the order parameter with the orthorhombic splitting b-a, which gives rise to the orthorhombic distortion anomaly at Tc as well as to the possibility of the additional second-order transition slightly below Tc is discussed.

Anomalous change in the photoacoustic phase near superconducting transition in YBa2Cu3O7

Photoacoustic amplitude and phase measurements have been carried out near the superconducting transition temperature in the highTcsuperconductor YBa2Cu3O7. In both the samples investigated, the photoacoustic phase undergoes an anomalous step-like decrease aroundTc≈ 96 K and increases at lower temperatures. A clear temperature hysteresis for the phase change has been noticed. No anomalous variation has been observed in the amplitude values. Neither phase nor amplitude shows any anomaly in a non-superconducting sample of the same composition.

Order-disorder transition in YBa2Cu3O7−x

The orthorhombic-to-tetragonal transition at ≈970K in the high-Tc superconductor YBa2Cu3O7−x is beleived to be an order-disorder transition. The linear ordering of the Cu O in the orthorhombic phase ( <970K ) is destroyed in the tetragonal phase. We have carried out a Monte Carlo simulation on a two-dimensional lattice involving 100×100 oxygen sites, which represents the basal plane of YBa2Cu3O7−x. There are only two parameters; the nearest neighbor O O repulsion energy and the O-site energy. The linear ordering of Cu O, twining along two-dimensional [11] (or three-dimensional [110]) and oxygen nonstoichiometry ( x>0 ) have been obtained in this model.

Superconductivity in Yba2Cu3O7–x in a 100 tesla magnetic field

The upper critical field (Hc2) of the high-Tc superconductor YBa2CU3O7–x (YBCO) is expected to be >100T at 0 K1–6. Because magnetic fields of >100 T can be produced only for a short time and by destructive methods, direct measurements of Hc2 at these field strengths have not so far been performed. Here we report the first observation of superconductivity at >100 T, using a method in which a voltage induced by a magnetization jump is measured in pulsed high magnetic fields. Superconductivity in YBCO was confirmed up to 101 T at 6 K.