Ion size effect on Tc in RBa2Cu3−χGaχO7−y systems (R=Er, Y, Dy, Eu and Nd)
01 Jul 1993-Physica C-superconductivity and Its Applications (North-Holland)-Vol. 212, Iss: 1, pp 119-127
TL;DR: In this article, the effect of Ga substitution for Cu in RBa2Cu3−χGaχO7−y (R=Er, Y, Dy, Eu and Nd) has been investigated for nominal composition χ=0, 0.05,0.1, 0.,15, 0,2 and 0.3, and at a constant Ga concentration, Tc decreases with increasing radius of the R ions.
Abstract: The effect of Ga substitution for Cu in RBa2Cu3−χGaχO7−y (R=Er, Y, Dy, Eu and Nd) has been investigated for nominal composition χ=0, 0.05, 0.1, 0.15, 0.2 and 0.3. The superconducting transition temperature Tc falls with increasing Ga concentration, and at a constant Ga concentration, Tc decreases with increasing radius of the R ions. We suggest that the decrease of density of states N(EF) or the localization of carriers due to Ga substitution are the possible mechanisms of superconductivity suppression. The superconducting-nonsuperconducting transition accompanied by a transition into the semiconducting phase in these systems is interpreted in terms of the Mott transition.
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TL;DR: In this paper, a comparison study of the calcination conditions for the synthesis of pure ReBa 2 Cu 3 O x phases (Re: Y, Nd, Eu, Gd, Dy, Ho, Er) by solid state reaction from Re 2 O 3, BaCO 3 and CuO was carried out.
Abstract: A comparison study of the calcination conditions for the synthesis of pure ReBa 2 Cu 3 O x phases (Re: Y, Nd, Eu, Gd, Dy, Ho, Er) by solid state reaction from Re 2 O 3 , BaCO 3 and CuO was carried out. X-ray diffraction analysis coupled with differential thermal analysis and hot-stage X-ray diffraction data were employed for this investigation. Thermal events occurring during reaction sequence and intermediate products are thoroughly discussed. It was found that the reaction rate for the ReBCO 123 phase formation depends on Re-ion size, decreasing as this size decreases and that the small Re-ion size powders present an increased instability. Due to their lower decomposition temperature and to their slower reaction rate, calcination of ReBCO systems of small Re ionic radius must be carried out at lower temperatures and at prolonged times. Calcination temperature can be increased when Re-ion size increases.
33 citations
TL;DR: In this article, the superconducting-nonsuperconducting transition accompanied by a transition into the semiconducting phase in these systems is interpreted in terms of a Mott transition, and the reduction of T c by Zn doping in RBa 2 Cu 3− x Zn x O 7− y was found to be strongly dependent on the ionic radius of the rare earth element R.
Abstract: Zn, having a definite valence state and filled 3d levels, is used for substituting Cu sites in RBa 2 Cu 3− x Zn x O 7⇔ y ( R = Yb , Er , Y , Dy , Gd , Eu , Sm and Nd ). Substitution of Zn for Cu in these systems causes a rapid nearly linear suppression of the superconducting transition temperature T c . All the RBa 2 Cu 3− x Zn x O 7− y samples are essentially single phase and retain the orthorhombic structure in the range of substitution (0≤ x ≤0.1). The reduction of T c by Zn doping in RBa 2 Cu 3− x Zn x O 7− y was found to be strongly dependent on the ionic radius of the rare-earth element R. The superconducting-nonsuperconducting transition accompanied by a transition into the semiconducting phase in these systems is interpreted in terms of a Mott transition.
27 citations
TL;DR: In this paper, magnetic susceptibility and resistivity measurements have been performed on 14 Tl(Sr1.5R0.5)CaCu2O7−δ compounds with R=La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu.
Abstract: DC magnetic susceptibility and resistivity measurements have been performed on 14 Tl(Sr1.5R0.5)CaCu2O7−δ compounds with R=La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu. All samples except the Ce-doped compound show superconducting phase transition temperature around 80–90 K. The rare-earth atoms behave as local moments above the superconducting transition temperature of these compounds. Mechanism of filling of holes in the CuO2 plane can be employed to interpret the suppression or enhancement of superconductivity by rare-earth ions in Tl(Sr1.5R0.5)CaCu2O7−δ.
20 citations
TL;DR: In this article, a large Nd1+xBa2−xCu3−yGayO7−δ single crystals measuring up to 22 × 15 × 3 mm have been obtained from an oxide flux which was stepwise cooled from 1030 to 960°C in air.
Abstract: Large Nd1+xBa2−xCu3−yGayO7−δ single crystals measuring up to 22 × 15 × 3 mm have been obtained from an oxide flux which was stepwise cooled from 1030 to 960°C in air. In the crystals the upper solubility limit of Nd is found to be x = 0.35 and that of Ga as high as y = 0.58. The Ga content is linearly related with that present in the molten solution. X-ray single crystal diffraction studies show that the tetragonal symmetry occurs in three states, i.e., (1) x ≥ 0.18, y = 0; (2) x = 0, y > 0.10 and (3) x + y ≥ 0.16. Optical polarizing microscopy reveals the twin domain structure existing in pure Nd1+xBa2−xCu3O7−δ crystals with x = 0.15. Transmission electron microscopy studies provide the evidence of the tweed tetragonal phase in the highly Ga-doped compound. The resistivity measurements reveal superconductivity of all samples with y ≤ 0.08, metallicity with y = 0.09–0.10, and semiconduction with y ≥ 0.15.
10 citations
TL;DR: In this article, the TlSr2(Ca1−xRx)Cu2O7 (Tl-1212) phase with R = Dy, Tb and Ho for x=01-06 has been studied by powder x-ray diffraction method and electrical resistance measurement All the samples showed a metallic normal state behavior.
Abstract: The TlSr2(Ca1−xRx)Cu2O7 (Tl-1212) phase with R = Dy, Tb and Ho for x=01–06 has been studied by powder x-ray diffraction method and electrical resistance measurement All the samples showed a metallic normal state behavior No correlation between ionic radius and Tc onset is observed The three series show the highest volume fraction (>97%) of Tl-1212 phase for x=05 The highest Tc onset does not correspond to the highest volume fraction The above results are explained as due to the mixed valence state of Dy and Tb in the Tl-1212 phase
7 citations
References
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01 Jan 1984
TL;DR: In the last fifteen years, there has been a noticeable shift towards impure semiconductors -a shift which came about because it is precisely the impurities that are essential to a number of major semiconductor devices.
Abstract: First-generation semiconductors could not be properly termed "doped- they were simply very impure. Uncontrolled impurities hindered the discovery of physical laws, baffling researchers and evoking pessimism and derision in advocates of the burgeoning "pure" physical disciplines. The eventual banish ment of the "dirt" heralded a new era in semiconductor physics, an era that had "purity" as its motto. It was this era that yielded the successes of the 1950s and brought about a new technology of "semiconductor electronics." Experiments with pure crystals provided a powerful stimulus to the develop ment of semiconductor theory. New methods and theories were developed and tested: the effective-mass method for complex bands, the theory of impurity states, and the theory of kinetic phenomena. These developments constitute what is now known as semiconductor phys ics. In the last fifteen years, however, there has been a noticeable shift towards impure semiconductors - a shift which came about because it is precisely the impurities that are essential to a number of major semiconductor devices. Technology needs impure semiconductors, which unlike the first-generation items, are termed "doped" rather than "impure" to indicate that the impurity levels can now be controlled to a certain extent."
1,904 citations
AT&T1
TL;DR: In this paper, a gettered annealing technique was employed to obtain homogeneous polycrystalline samples of oxygen deficient Ba/sub 2/YCu/sub 3/O/sub 7-sub delta/ for 0less than or equal todeltaless than and equal to 0.7.
Abstract: Employing a gettered annealing technique, we have prepared homogeneous polycrystalline samples of oxygen deficient Ba/sub 2/YCu/sub 3/O/sub 7-//sub delta/ for 0less than or equal todeltaless than or equal to0.7. Measurements of resistive T/sub c/, resistivity, magnetization, and lattice parameter indicate that a distinct bulk superconducting phase with a T/sub c/ of 60 K occurs in the range of 0.3
726 citations
AT&T1
TL;DR: In this paper, the dependence of both superconducting and normal-state properties on oxygen stoichiometry has been investigated, and it has been shown that the properties of the normal state are strongly affected by the microscopic state of the oxygen subsystem.
Abstract: Probably the most unusual crystal-chemical aspect of the new high-temperature oxide superconductors is their significant variability in oxygen content. For the YBa2Cu3O7–δ family of compounds, the oxygen stoichiometry varies in the range 0 < δ < 1 under normal synthetic conditions, with the optimal 91-K superconductive transitions obtained near δ=0 (see, for example, ref. 1). Work presented so far on the dependence of both superconducting and normal-state properties on oxygen stoichiometry has considered only the value of δ in YBa2Cu3O7–δ. Here we present data that indicate the issue to be considerably more interesting and complex, and propose that the microscopic variables thus far not considered include the distribution of oxygen over the available sets of sites in the structure, with that distribution strongly dependent on synthetic conditions. In addition to the dependence of the bulk transition temperture (Tc), normal-state resistivity and crystallographic symmetry on the microscopic distribution, we find the magnitude of the magnetic susceptibility in the normal state to be strongly affected by the microscopic state of the oxygen subsystem. We also report the existence of a single-phase 60-K bulk superconductor at stoichiometry YBa2Cu3O6.6–6.7, which we postulate to have an ordered array of oxygen vacancies, and two distinct plateau regions in the variation of Tc with x which are either unobserved or only hinted at under other synthetic conditions.
383 citations
TL;DR: In this article, the authors investigated superconductivity in a series of alloyed compounds, YBa2 (Cu1-xMx)3O7-δ with M = Fe, Co, Ni, Zn and Ga, in which metals M are partially substituted for Cu.
Abstract: In spite of an overwhelming amount of research work1 triggered by the discovery2 of superconductivity above 90 K in an Y–Ba–Cu oxide, fundamental questions regarding the origin and mechanism of the high-Tc superconductivity in YBa2Cu3O7–δ remain to be answered. Specifically, it has not been decided which of the two Cu sites mainly carries superconducting electrons. As an approach to the problem, we investigated superconductivity in a series of alloyed compounds, YBa2 (Cu1–xMx)3O7–δ with M = Fe, Co, Ni, Zn and Ga, in which metals M are partially substituted for Cu. The electrical resistivity measurements, as well as the X-ray analysis at low temperatures, show that Tc is not sensitive to the orthorhombic-tetragonal phase transition induced by the impurities, thus strongly suggesting that superconductivity along the one-dimensional Cu–O chains is unlikely.
277 citations
TL;DR: The results indicate that the oxygen-vacancy order, or the linear-chain structure, is not essential, and it is found that the Cu(2) sites are much more crucial than theCu(1) sites in sustaining the high ${T}}_{\mathrm{c}}$.
Abstract: We used Zn and Ga, two unique dopants having definite valence states and filled 3d levels, to substitute preferentially on the Cu(2) and Cu(1) sites in the ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7}$ superconductor. Small doping of Ga induces an orthorhombic-to-tetragonal structural transition, but the values of ${\mathrm{T}}_{\mathrm{c}}$ are as high as 81 K in the tetragonal phase. Our results indicate that the oxygen-vacancy order, or the linear-chain structure, is not essential. We also find that the Cu(2) sites are much more crucial than the Cu(1) sites in sustaining the high ${\mathrm{T}}_{\mathrm{c}}$.
262 citations