Number Of CuO2 Layers Research Articles

Structure and Magnetic Properties of Hydrothermal-Treated Cu–Zn Ferrite/CuO Multilayers

The Cu0.8Zn0.4Fe2O4 ferrite/CuO multilayers (CZF ML) were obtained by RF sputtering. These ML were given hydrothermal heat treatment for phase stabilization. The X-ray diffraction pattern show the CZF spinel ferrite phase in all the multilayered films. The CuO-monoclinic phase appeared as the number of CuO layers (n) increased. The field emission electron micrographs show clear nonmagnetic (NM) CuO separations with columnar growth structure for the multilayers. The micrographs in surface view show uniform cluster distribution. The magnetization (M(H)) plots at 80 and 300 K show anisotropy as a function of angle between applied field (H) and ML surface. The oscillatory magnetization behavior is observed for H perpendicular to ML surface. It is more pronounced when H is perpendicular to ML surface than when it is parallel to it. At low temperature, the increased saturation magnetization is observed due to ferromagnetic cluster formation. The structural-induced magnetic anisotropy is verified using FMR spectra of the ML films with a number of NM separations.

Variation of Isotope Coefficient with Number of CuO2 Layers in High TC Superconductors

In this paper, an effort has been made to study the isotope coefficient in high TC Superconductors by using the variation of isotopic coefficient with the number of CuO2 layers and the variation of isotope coefficients on transition temperature TC . The Hamiltonian for CuO2 layers using BCS type model and extra term of interlayer interaction between CuO2 layers has been considered. Expressions for isotope effect (α) and transition temperature (TC) are obtained and numerically calculated for experimental values by using Green’s function technique.

Low Frequency Raman Modes of Bi<sub>2 −x </sub>Pb<sub>x</sub>Sr<sub>1.6</sub>Ln<sub>0.4</sub>CuO<sub>6</sub> <sub>−δ</sub>

Raman measurements were made on polycrystalline Bi2xPbxSr1:6Ln0:4CuO6 for Ln=fLa,Nd, Sm, Eug with various x and doping states. Our measurements suggest a signi cant Bicontribution to the 118cm1 mode but not to the 70cm1 mode which instead shifts to lowerfrequencies with increasing number of CuO2 layers in the Bi-based family. Shifts in the O(2)Srapical oxygen mode can be attributed to unit cell contraction within experimental error.

Material and Doping Dependence of the Nodal and Antinodal Dispersion Renormalizations in Single- and Multilayer Cuprates

We present a review of bosonic renormalization effects on electronic carriers observed from angle-resolved photoemission spectra in the cuprates. Specifically, we discuss the viewpoint that these renormalizations represent coupling of the electrons to the lattice and review how materials dependence, such as the number of CuO2layers, and doping dependence can be understood straightforwardly in terms of several aspects of electron-phonon coupling in layered correlated materials.

An explanation for a universality of transition temperatures in families of copper oxide superconductors.

A remarkable mystery of the copper oxide high-transition-temperature (T(c)) superconductors is the dependence of T(c) on the number of CuO2 layers, n, in the unit cell of a crystal. In a given family of these superconductors, T(c) rises with the number of layers, reaching a peak at n = 3, and then declines: the result is a bell-shaped curve. Despite the ubiquity of this phenomenon, it is still poorly understood and attention has instead been mainly focused on the properties of a single CuO2 plane. Here we show that the quantum tunnelling of Cooper pairs between the layers simply and naturally explains the experimental results, when combined with the recently quantified charge imbalance of the layers and the latest notion of a competing order nucleated by this charge imbalance that suppresses superconductivity. We calculate the bell-shaped curve and show that, if materials can be engineered so as to minimize the charge imbalance as n increases, T(c) can be raised further.

Calculated Spectral Properties of Bi–Sr–Ca–Cu–O Films

The electronic structure of high-Tc superconducting Bi–Sr–Ca–Cu–O thin films was calculated. On the basis of the results of band calculation, total and projected densities of electronic states as well as X-ray emission OKα and CuLα and photoelectron spectra for each film were calculated. The dependence of the electronic structure and spectra on the number of CuO2 layers in the unit cell of the films is discussed.

The influence of oxygen content on the Tc of HTS Hg-1245

We have observed an extraordinary behavior of the HgBa2Ca4Cu5O12+δ layered HTS (phase 1245) in the overdoped state. Earlier we have synthesized the phase Hg-1245 with different oxygen content and consequently different values of the lattice parameter a. We have observed a coincidence of a values when the Tc(a) cupolas reach their maxima for phases Hg-1223, 1234, and 1245, and a merging of their overdoped parts together with abrupt falling off of the Tc values. The Hg-1245 phase has shown the most unusual behavior. Contrary to other phases, this one contains three types of CuO2 layers in a unit cell. We supposed that, in the case of the Hg-1245 phase, the holes coming from the reservoir, which is the Hg–O plane, cannot reach the “far” CuO2 layer which is notable for this phase. We have calculated the hole concentration for each layer for 1223, 1234, and 1245 phases. The results obtained confirm our assumption. The hole concentration appears negligibly small for the overdoped 1245 phase. We can consider the “fifth” CuO2 layer as not taking part in superconductivity. The analysis of the behavior of the Tc(a) cupolas for the phases with different number of CuO2 layers and of hole density distribution between the layers has been carried out.

Systematics in Bi-2201, -2212 and -2223 superconductors studied by positron annihilation radiation measurements

Positron lifetimes in Bi 2Sr 2Ca ( n−1) Cu n O (2 n+4+ δ) or Bi-22( n−1) n superconducting compounds for n=1, 2 and 3 have been determined from positron annihilation lifetime (PAL) spectroscopy of associated γ-radiations. Bulk lifetime is shown to increase systematically with increase of n, the number of CuO 2-layers in the Bi-22( n−1) n compound. Positron annihilation probing of structural units of this perovskite-like crystal system has thus been demonstrated.

Electronic structure and spectral characteristics of Bi-Sr-Ca-Cu-O films

The electronic structure of high-temperature superconducting films of Bi-Sr-Ca-Cu-O is determined using the linearized augmented plane wave method. Total and local partial densities of states are calculated for each film using the results of band structure calculations. Theoretical OKα and CuLα X-ray emission spectra are found. The dependence of the electronic structure and spectra on the number of CuO2 layers in the unit cell is discussed.

Uniformly layered mixtures of the Bi2Sr2Can−1CunOn+4 phases formed in artificially layered films—structural analysis and superconducting properties

Uniformly layered mixtures of the succeeding members of Bi2Sr2Can−1 CunO2n+4 series were found in the films synthesized by alternating sputter deposition of BiO, SrCu0.5O1.5, and CaCuO2 layers. The uniformly layered intergrowth was caused by the deviation of the CaCuO2 supply amount in each sequence, which is constant throughout the synthesis, from the stoichiometric amount. It is presented that the x-ray diffraction peaks from the films with uniform intergrowth can be indexed by treating them as the satellites of superlattices. In this treatment, the number of CuO2 layers, which varies randomly but uniformly along the c axis, is expressed on average by noninteger n. The superconducting transition temperature (Tc) and concentration of holes in the CuO2 layers in those films decreased with increasing n (2.88≤n≤6) monotonically. From the continuity of the decrease in Tc with n, we conclude that the hole concentration is averaged between the two phases in the intergrowth by the diffusion of the holes.

Acoustic plasmon exchange in multilayered systems: II. application to high-Tc superconductors

For pt.I see ibid., vol.4, p.1799, 1992. A theory for high-Tc superconductivity has been developed using the Eliashberg model on the basis that the attractive interaction is provided by the Plasmon-mediated effective interaction between the charge carriers. Calculation of Tc using these interactions, presented in paper I, shows that Tc should rise, with a saturation effect, with the number of CuO layers per unit cell, which is in agreement with observations in the Tl- and Bi-based compounds. Furthermore, this theory shows that a short coherence length is an essential requirement for superconductivity at high temperature.

The Systematics of Irreversibility in Superconducting Thallium Cuprates

ABSTRACTThe irreversibility lines, Hirr(T), for the series of superconducting compoundsTlmA2CunO2+m+2n, where A is Ba or Sr, are measured between 0 and 1 tesla for m = 1,2 and n = 1,2,3 and 4 and show a marked steepening with decreasing anisotropy i.e. as m is lowered from 2 to 1. In addition, for m=2 material Hlrr(T) is observed to steepen with decreasing number of CuO2 layers. The hole dependence of the irreversibility line is also investigated in TI2Ba2CuO6+6 by changing the oxygen stoichiometry, 6. Hirr(T) progressively steepens with increasing hole concentration on the overdoped sida of Tc(max). These results are consistent with a model of flux motion arising from a crossover from 3-D vortex lines to 2-D pancake vortices which are decoupled in the c-direction, and provide guidance for materials selection and optimum doping.

New polytypoids of the Y-Ba-Cu-O 123 compound

Stoichiometry-induced deviations of the perfect stacking order in Y-Ba-Cu-O 247 samples are investigated. Several new phases are observed which can be described as polytypoids or as shear structures of the 123 structure, and which differ from the known compounds by the number of 123 cells per unit cell, or by the number of CuO layers in an interleaving CuO multilayer.

Resistive transition curves in magnetic fields for Tl2Ba2Can-1CunOy (n=1, 2, 4) compounds: Dependence on the number of Cu-O layers.

A systematic measurement of the superconducting resistive transition curves in magnetic fields has been performed for ${\mathrm{Tl}}_{2}$${\mathrm{Ba}}_{2}$${\mathrm{Ca}}_{\mathit{n}\mathrm{\ensuremath{-}}1}$${\mathrm{Cu}}_{\mathit{n}}$${\mathrm{O}}_{\mathit{y}}$ (n=1, 2, 4) compounds. It is found that the broadening of the transition curves varies systematically with the number of Cu-O layers (i.e., the value n). The slope of the field-versus-temperature curves in fields parallel to the c plane increases with decreasing n, while the slope in perpendicular fields is almost independent of n. This result suggests that the upper critical fields and the coherence lengths of these compounds have a strong correlation with n. It is concluded that the coherence length along the c axis of ${\mathrm{Tl}}_{2}$${\mathrm{Ba}}_{2}$${\mathrm{CuO}}_{\mathit{y}}$ is smaller than the thickness of the Tl-O-layer region. According to the Josephson-coupled layer model, ${\mathrm{Tl}}_{2}$${\mathrm{Ba}}_{2}$${\mathrm{CuO}}_{\mathit{y}}$ is expected to be a two-dimensional superconductor.

Electronic structure of Tl[sbnd]Ba[sbnd]Ca[sbnd]Cu[sbnd]O high Tc superconductors

We discuss the variation of total and projected electronic densities of states at the Fermi level in the TlBa2CaL−1Cu3O2L+3 series for L= 1 to 5. Simple BCS-type theories relating Tc to N(EF) suggest that only the broad CuO bands contribute to superconductivity, since the inclusion of narrow TlO band contributions to N(EF) leads to an irregular variation of N(EF) with the number of CuO2 layers. Other important band structure features are also considered.

Microstructure and superconductivity in a new superconductor series: (Tl,Pb)1Sr2Can−1CunO2n+3−δ

The synthesis procedure and superconducting properties of the first two members of the new series of superconductors of a general formula: (Tl, Pb)1 Sr2 Can−1 Cun O2n+3−δ , are reported. The detailed atomic level microstructure of the compounds have been determined and computer simulated with structural models. Tc increases with n, the number of Cu-O2 layers per unit cell, as in the single Tl-layer Tl-Ba-Ca-Cu-O compounds, but the new materials have higher Tc ’s for the same value of n.

Correlations between the superconducting transition temperatures and the in-plane copper-oxygen bond lengths in the copper-oxide superconductors

Examination of the superconducting temperatures Tc and the in-plane Cu-O bond lengths rCuO of the Tl- and Bi-based copper-oxide superconductors reveals the Tc vs. rCuO characteristics similar to those found for La2−xSrxCuO4. The Tc vs. rCuO correlations are grouped into three major classes according to the size of the cations occupying the 9-coordination sites. The available data strongly suggest that two major classes comprising multi-CuO2 layer phases are each made up of subclasses of Tc vs. rCuO correlations distinguished by the number of CuO2 layers in a formula unit. In each class or subclass of Tc vs. rCuO correlations, there exists an optimum Cu-O distance (i.e., ropt) for which Tc is maximum so that shortening rCuO increases Tc for rCuO >ropt, but decreases Tc for rCuO<ropt. These observations and their implications are examined in terms of the overlap populations of the in-plane Cu-O bonds calculated as a function of the number of electrons in the x2−y2 bands of the CuO2 layers. Several experimental results are discussed on the basis of the Tc vs. rCuO correlations.

Preparation of the bulk superconductor Tl 2Ba 2Ca 3Cu 4O 12

The bulk superconductor Tl 2Ba 2Ca 3Cu 4O 12 with T c (onset) above 112 K has been prepared and structure and chemical composition were examined by X-ray powder diffraction, analytical (EDX) and high resolution electron microscopy. Unit cell dimensions for the tetragonal cell determined by the least squares method are a = 3.853 (1) A ̊ , c=41.98 (3) Å. The transition temperature, T c, of the double layered Tl system increases with the number of Cu-O layers ( n) up to n = 3, while it turns down at n = 4.

New Tl-Ba-Ca-Cu-O (1234 and 1245) superconductors with T/sub c/&amp;lt;117 K

TlBa/sub 2/Ca/sub 3/Cu/sub 4/O/sub 11/ (1234) and TlBa/sub 2/Ca/sub 4/Cu/sub 5/O/sub 13/ (1245) superconductors have been synthesized for the first time. The compounds have T/sub c/ values of 116 approximately 122 K. The highest T/sub c/ value was obtained for the 1234 phase. These are single Tl-O layer compounds with less than half the Tl content of the previous 2223 phase. The structure of the compounds is a simple tetragonal phase with the lattice constants of a=b=3.85 AA and c=19.1 AA for the 1234 phase and a=b=3.85 AA and c=22.3 AA for the 1245 phase. The electron diffraction patterns and the lattice images from a high-resolution TEM have confirmed an oxygen-deficient layered-perovskite structure with the P4/mmm space group. The c-lattice constant follows the c-axis rule of a linear relation of c=6.3+3.2 n (n=the number of Cu-O layers), The T/sub c/ value is strongly related to the valence of Cu ion.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

SUPERCONDUCTIVITY IN THE Tl-Ca-Ba-Cu-O SYSTEM: SYNTHESIS, CHARACTERIZATION AND MECHANISM

Synthesis and characterization of some of the members of the Tl-Ca-Ba-Cu-O system are presented. T c in both the TlCa n−1 Ba 2 Cu n O 2n+3 and Tl 2 Ca n−1 Ba 2 Cu n O 2n+4 series increase with the number of Cu-O layers, n; T c in the latter series with two Tl-O layers are generally higher than in the former with a single Tl-O layer. Tl in the cuprates is in the 3+ state while Cu is in the 1+ and 2+ states, showing the importance of oxygen holes. The concentration of these holes seems to increase with the number of Tl-O layers.