YBCO Family Research Articles

Electronic properties of Y-247 ceramic via computational method

Y2Ba4Cu7Ox (Y-247) is one of the phases that came from the YBCO superconductor family. The superconductor has been studied through the computational method by applying the Density Functional Theory (DFT) via the first principles study. The structural of the pure Y-247 have been constructed in the Material Studios software and the electronic properties of the material were calculated and optimized using Generalized Gradient Approximation Perdrew Burke Ernzerhof (GGA PBE) and Local Density Approximation (LDA) exchanged correlation with OTFG Ultrasoft. From the band structure analysis, the pure Y-247 pseudogap observe above the fermi level and overlapped from the valance band to the conduction band. It is also shown that the conduction band and valence band overlapped each other for other phases, showing the conducting properties of the structure. Different pseudogap shown for both of the exchange correlation due to overbinding in GGA exchange correlation. Different phases for YBCO family shown difference in pseudogap due to the temperature dependance for each phases. For density of states, copper 3d orbital state and oxygen 2p state shows important role to maintaining the superconducting properties with electron-hole migration concept.

Enhanced magnetic properties of YBa2Cu3O7−δ bulk superconductors with tailored structure by a novel seeding assembly

YBa2Cu3O7−δ (YBCO) bulk superconductors are regarded as the most promising alternatives for conventional permanent magnets as they provide high field trapping capacity at low temperatures. However, for further improving their superconducting properties, it remains a significant challenge to enlarge the c growth sector by large-sized seeds or multi-seeds while maintaining the microstructure with a low porosity or clean grain boundaries that enables their performance. Here, we report a novel seeding assembly approach by vertically-connecting strip-seeds for inducing potential [110]-oriented overgrowth. Initially, from naturally right-angled corners, YBCO rapidly crystallized to form kite-liked convex areas, which, together with the original seed, effectively functioned as a large-sized seed to generate a sizable c growth sector. The novel-seeded sample exhibited a promising structure not only free of grain boundaries, but also with a favorable porosity of 20.29%. Such a low value is similar to 19.77% of the small-seeded one and much lower than 34.20% of the large-seeded one. Finally, due to structure tailoring towards an enlarged c growth sector with maintained pore characteristics, high and mono-peak trapped fields of 16 mm diameter YBCO bulks were reliably attained, up to a record value of 0.7025 T. This work offers insights into design principles for boosting magnetic properties of other members in the YBCO family.

An in situ self-assembly strategy for exact-(110)-plane-controlled crystallization of high-performance YBa2Cu3O7−δ single grains

YBa2Cu3O7−δ (YBCO) single grain, as a pivotal and popular oxide ceramic, is of great importance in practical applications for its considerable potential in magnetic properties. Normally, sizable YBCO bulk superconductors are fabricated by multi-seeded melt-growth for time saving. However, the performance of such bulks has long suffered from certain methodological barriers related to artificially induced imperfect-seeding, involving unreliable precision in seeding alignment and detrimental impact on grain boundaries. Here, a facile but effective in situ self-assembly (ISSA) strategy is reported for seeding structural design, in which exactly (110)/(110)-aligned twin-seeds naturally arise through the self-replication of crystallographic orientation from one small seed during thermal procedure. Distinctively, after two induced grains impinging, a [110]-oriented growth zone emerges and expands to the edge of the sample, leading to a contamination-free homo-combination. As a result, 25 mm diameter fully-grown bulks with single-grain quality were reliably attained, which exhibited superior levitation forces up to 65.1 N and field trapping capability up to 0.8943 T with a prominent feature of mono-peak. The ISSA seeding strategy in this work, with its nature in achieving exact seeding alignment, is widely applicable for the preparation of other high-performance bulks in the YBCO family.

Механизмы, определяющие гистерезис магнитосопротивления гранулярного ВТСП в присутствии парамагнитного вклада, на примере HoBa-=SUB=-2-=/SUB=-Cu-=SUB=-3-=/SUB=-O-=SUB=-7-delta-=/SUB=-

The hysteretic magnetoresistance of granular high-temperature superconductor (HTSC) HoBa2Cu3O7-δ is investigated. Superconductors of the YBCO family with magnetic rare earth elements (Nd, Ho, Er, Sm, Yb, Dy) in place of yttrium are characterized by a significant paramagnetic contribution to the total magnetization. Impact of this paramagnetic contribution on the magnetotransport properties is analyzed using the concept of an effective field in an intergranular medium. Lines of magnetic induction from paramagnetic moments do not concentrate in intergranular boundaries, and, thus, have an insignificant effect on magnetotransport properties of granular HTSC. At the same time, there are strong concentration of magnetic flux in the intergranular boundaries due to Meissner currents and Abrikosov vortices. This magnetic flux compression determines the magnetotransport properties of granular HTSCs, including YBCO with magnetic rare earth elements.

On the Nature of Magnetic Oscillations in YBCO High-Temperature Superconductors

Possible causes of magnetic oscillations with a low frequency of about 2% of the Brillouin zone, observed in high-temperature superconductors of the YBCO family, are studied. A scenario is proposed in which the observed frequency is proportional to the difference of the bilayer-split closed pockets in the Fermi surface rebuilt due to scattering to charge-density-wave vectors. A method is proposed for experimental determination of which of the four possible scenarios for the rise of these magnetic oscillations is realized in YBCO.

О природе магнитных осцилляций в высокотемпературных сверхпроводниках YBCO

AbstractPossible causes of magnetic oscillations with a low frequency of about 2% of the Brillouin zone, observed in high-temperature superconductors of the YBCO family, are studied. A scenario is proposed in which the observed frequency is proportional to the difference of the bilayer-split closed pockets in the Fermi surface rebuilt due to scattering to charge-density-wave vectors. A method is proposed for experimental determination of which of the four possible scenarios for the rise of these magnetic oscillations is realized in YBCO.

II Tip süperiletkenlerde manyetik kaldırma kuvvetinin bir karşılaştırmalı çalışması

Meissner Effect is, of course, an essential characteristic of a superconductor besides the zero resistivity since the discovery by Meissner and Ochsenfeld in 1933. They showed by experiment that the magnetic field inside a superconductor is always zero. This implies that we can think of a superconductor as being a perfectly diamagnetic material. It is highly attractive for the technological applications of the type-II (High temperature) superconductors as YBa2Cu3O7, Bi2Sr2Ca2Cu3O10 and HgBa2Ca2Cu3O8. One important property is the levitation force and its MagLev application. MagLev systems have become very important in the transportation and other applications. These applications are ranging from in an energy efficient prototype of a cryogen transfer line to in space energy storage systems. In this study, we compared that the effect of magnetic levitation force BSCCO and YBCO superconductors. The results were showed that the BSCCO superconductor’s family is very poor in case of the levitation force compared with the YBCO superconductors. It may be attributed that the YBCO family superconductors have the high critical current density which occurs in the case of the flux pinning and the high magnetization behavior.

Charge Distribution in YBa<sub>2</sub>Cu<sub>3</sub>O<sub>7 </sub> and YBa<sub>2</sub>Cu<sub>4</sub>O<sub>8 </sub>by Density Functional Theory

In this work, we analyze the electronic structure and charge distribution of the YBCO family compounds Y-123 and Y-124 bulk using the density functional theory. The band structures and the density of states of the compounds are shown. The charge transfers between the atoms in the two compounds are compared and discussed in detail. The lattice parameters obtained by Broyden-Fletcher-Goldfarb-Shanno (BFGS) algorithm are compared with the experimental parameters. The critical differences of the charge distribution for these two compounds are discussed.

An Approach to Synthesis a New Superconductor Belonging to the YBCO Family: Y2Ba5Cu7O x

An approach to synthesis a novel high-temperature superconductor, Y2Ba5Cu7O x , is presented. The synthes is method was based on the standard solid-state reaction at ambient pressure. The structural parameters and space group were studied using the X-ray diffraction (XRD) technique and the experimental results were refined by the Rietveld method. The XRD results show that the major phases include peaks corresponding to Y123 and Y124 structures with minor shifts as well as a few small peaks representing BaCuO 3 as an impurity. The electrical transport properties of the sample were investigated in the 60–300 K temperature range in the presence of magnetic fields up to 15 kOe. The electrical resistivity of the synthesized compound shows a transition to a superconducting state at $T_{c}^{on}$ = 98 K and zero resistivity at $T_{c}^{off}$ = 92 K which are higher than those of YBa 2Cu 3O7−δ and comparable to the transition temperatures of Y 3Ba 5Cu 8O y . Application of a magnetic field leads to broadening of the tail part of the resistivity versus temperature plots in the mixed states and causes a reduction in $T_{c}^{offset}$ .

Influence of Ag/Cu Substitution on Structural Effect of New High Temperature Superconductor Y3Ba5Cu8O18

The class of superconductors ceramic materials has been made from copper oxides mixed with rare earth elements such as yttrium. The new Y-based high temperature superconductor Y3Ba5Cu8O18-δ (Y358), Gholipour et al. (2012), Tavana et al. (2010), Khosroabadi et al.(2014), with Ag/Cu substitution was synthesized through the sol-gel technique by making nano oxide Y, Ba, Cu and Ag. The influence of the doping of Ag atoms into the compound Y3Ba5Cu8O18 was studied by employing XRD pattern, SEM and the electrical resistivity measurements. The room temperature electrical measurements have shown that ceramic Y358 has metal behavior in the normal state. The compound of YBCO family was discovered containing the CuO2 planes and the Cu-O chains. It seems that increasing the number of the CuO2 planes and the position of the Cu-O chains have positive effects on the value of the transition temperature in the Y-based compounds. The analysis of the X-ray diffraction pattern was approved by MAUD software which the Ag ions substitute in symmetrical phase of the sample. The substitution of the Ag ions in the CuO2 plane of symmetric phase has been compared with the Ag ions in the Y123 superconductor, which substitute in the Cu-O chain. The electrical resistivity of these superconductors was measured by 4prob method. The electrical resistivity graph approved the start of transition temperature above 100K.

Plane speaking

Small Fermi surfaces have been observed by quantum oscillations in the YBCO family of copper oxide superconductors, but until now it has been unclear whether they are specific to YBCO or universal to all underdoped cuprates.

How Tc can go above 100 K in the YBCO family

We report the results of the electronic structure calculation of a newly discovered member of the YBCO high-Tc family, i.e., Y3Ba5Cu8O18 (Y358) with Tc>100, based on the full-potential linearized augmented plane waves method (FP-LAPW) of density functional theory in the generalized gradient approximation (GGA). The evolution of the number of hole carriers in different sites of the CuO2 planes and CuO chains has been investigated in comparison with the other YBCO family members, i.e., Y123, Pr123, Y124, and Y247. The results suggest that pumping hole carriers out of the chains toward the planes enhances the transition temperature. The band structure calculations have been performed for Y358, and the results show similar features with the other family members. Most notably, a van Hove singularity forms near the X point of the Brillouin zone below the Fermi level and within the energy of the buckling phonon mode, for which the interplay is discussed.

Correlation between incoherent phase fluctuations and disorder inY1−xPrxBa2Cu3O7−δepitaxial films from Nernst effect measurements

Measurements of Nernst effect, resistivity and Hall angle on epitaxial films of Y$_{1-x}$Pr$_x$Ba$_2$Cu$_3$O$_{7-\delta}$(Pr-YBCO, 0$\leq x\leq$0.4) are reported over a broad range of temperature and magnetic field. While the Hall and resistivity data suggest a broad pseudogap regime in accordance with earlier results, these first measurements of the Nernst effect on Pr-YBCO show a large signal above the superconducting transition temperature(T$_c$). This effect is attributed to vortex-like excitations in the phase incoherent condensate existing above T$_c$. A correlation between disorder and the width of the phase fluctuation regime has been established for the YBCO family of cuprates, which suggests a T$_c\approx$110K for disorder-free YBa$_2$Cu$_3$O$_{7-\delta}$.

Pair breaking by chain oxygen disorder in light-ion irradiatedYBa2Cu3Oxthin films

We report on the effect of oxygen disorder in the CuO chains on the superconducting properties of oxygen depleted YBa_(2)Cu_(3)O_(x)(YBCO). While moderate disorder, induced thermally, depresses the critical temperature as a result of a reduced carrier concentration, strong oxygen disorder and chain fragmentation induced by low energy (80 keV) He^(+) irradiation suppresses the critical temperature beyond the values expected from the reduction of the carrier density. This provides an experimental evidence of pair breaking by chain disorder and outlines the importance of chain states in the pairing mechanism in the YBCO family.

89Y NMR SPECTRA AND RELAXATION IN UNDERDOPED AND OVERDOPED REGIMES OF SUPERCONDUCTING Ca-DOPED YBCO6 AND YBCO7

The results of a study of 89 Y NMR line shape and Knight shift, of the spin-echo dephasing time and of spin lattice relaxation time in Ca-doped YBCO compounds are presented. The underdoped and the overdoped regimes are achieved by means of Ca 2+ for Y 3+ substitutions in the parent antiferromagnet YBa 2 Cu 3 0 6.1 and in the chain-full YBa 2 Cu 3 0 7, respectively. The experimental findings are discussed in the light of models of localized Cu 2+ electrons and of delocalized Fermi-like carriers with antiferromagnetic correlation. Insights are obtained in regards of the density of states evolution with doping and of the occurrence, in the underdoped regime, of low-energy magnetic excitations causing a divergence of the relaxation rates on cooling, accompanied by a concurrent broadening of the NMR line. It is argued how a revision of the commonly accepted view for the microscopic magnetic properties in the YBCO family is required in order to attain a comprehensive justification of the variety of experimental data.

A Computer Simulation Study of Lithium Diffusion in the 123 and 124 Superconductors

Atomistic computer modelling has been applied to the structure of the YBCO family of superconductors, and the diffusion profiles of Li+ ions through the barium channels. The calculated structures agree well with the experimental data for both the 123 and 124 structures. However a slight modification to the 124 structure is suggested which we believe is consistent with experimental evidence. The calculated activation energy for Li+ diffusion approximate to 0.8eV in the 124 agrees well with experimental measurements. An hypothesis is suggested for the difficulty encountered in synthesising the 125 structure.

The Pairing State of High Temperature Superconductors: Magnetic, Thermal and Microwave Measurements on a Single Crystal

The pairing state has been studied through measurements of the transvers magnetic moment in the nonlinear Meissner regime. This investigation, which probes properties over a volume determine by the penetration depth, and is thus a bulk measurement, does not support a pure \em{d}-wave picture of the pairing state. The crystal on which much of the data has been obtained was subject to other experimental investigations which reveal it to be of a quality comparable to those of the best cuprate crystals in the YBCO family. These include measurements of the specific heat in magnetic fields, both near the transition temperature and at low temperatures, the measurement of microwave properties leading to the temperature dependences of the penetration depth and the surface resistance at low temperatures. Only the microwave measurements were unequivocally in agreement with the findings of others which have been interpreted as being supportive of $\em{d}$-wave pairing. This suggests that it is necessary to seek alternative explanations for some data interpreted within a \em{d}-wave framework.