B. G. Bagley

Bio: B. G. Bagley is an academic researcher from Telcordia Technologies. The author has contributed to research in topics: Superconductivity & Oxide. The author has an hindex of 19, co-authored 41 publications receiving 1988 citations.

Crystal substructure and physical properties of the superconducting phase Bi4(Sr,Cr)6Cu4O16+x.

Abstract: We have isolated a high-T/sub c/ phase in the Bi-Sr-Ca-Cu-O system of composition Bi/sub 4/(Sr,Ca)/sub 6/Cu/sub 4/O/sub 16/..mu../sub x/. The crystal substructure has a tetragonal unit cell (a = 3.817 A, c = 30.6 A) with similarities to both the oxygen-defect perovskites YBa/sub 2/Cu/sub 3/O/sub 7/..sqrt../sub x/ and the K/sub 2/NiF/sub 4/ structure of La/sub 2/CuO/sub 4/. The oxygen content, determined by titration and thermogravimetric analysis (TGA) experiments, corresponds to a formal oxidation state Cu(2.15). Oxygen can be reversibly depleted in an argon ambient in an amount corresponding to the reduction of the Cu(III) into Cu(II). The compound has a metalliclike resistance above its T/sub c/ near 85 K. Processing this precursor compound by heating to temperatures near its melting point (885 /sup 0/C) produces a sharp resistivity drop near 110 K that we show by ac susceptibility and Meissner effect is due to a superconducting transition.

Preparation, structure, and properties of the superconducting compound series Bi 2 Sr 2 Ca n-1 Cu n O y with n=1, 2, and 3

Abstract: Crystals of the three Bi-based cuprates of general formula ${\mathrm{Bi}}_{2}{\mathrm{Sr}}_{2}{\mathrm{Ca}}_{n\ensuremath{-}1}{\mathrm{Cu}}_{n}{\mathrm{O}}_{y}$ with $n=1,2, \mathrm{and} 3$ have been isolated and their structural and physical properties investigated. The structures are similar, differing only in the number of Cu${\mathrm{O}}_{2}$-Ca-Cu${\mathrm{O}}_{2}$ slabs packed along the $c$ axis. The insertion of one and two slabs increases $c$ from 24.6 to 30.6 and 37.1 \AA{}. Transmission electron microscopy shows there are stacking faults within the crystals in agreement with our x-ray data and its analysis. Resistivity, ac susceptibility, and dc magnetization measurements demonstrate superconductivity in the $n=1,2, \mathrm{and} 3$ phases at 10, 85, and 110 K, respectively. The observed transition temperatures and the stacking fault densities are dependent upon sample processing, in particular, the annealing temperatures and cooling rates. The transition temperature is, within the accuracy of our chemical titration, independent of the average copper valency that was determined to be 2.15 \ifmmode\pm\else\textpm\fi{} 0.03 for each of the three compounds.

Origin of the 110-K superconducting transition in the Bi-Sr-Ca-Cu-O system.

Abstract: Superconducting critical transitions with an onset at 112 K and zero resistance at 107 K are obtained within the Bi-Sr-Ca-Cu-O system. The synthesis and formation of the 110-K superconducting phase using the 85-K material as a precursor is explained. The 110-K phase grows from the 85-K phase such that the resulting faceted crystal (a pseudomorph) can contain some of the 85-K phase in the core. With such a microstructure our magnetic data can be simply explained. A major structural difference between the 85- and 110-K materials is that the 85-K material can grow (relatively) large single crystals having long-range order whereas the 110-K material has only intermediate-range order (cryptocrystalline) of about 100--200 A.

Bulk and thick films of the superconducting phase YBa2Cu3O7−y made by controlled precipitation and sol‐gel processes

Abstract: The synthesis of high‐temperature superconducting oxides using solution chemistry has been investigated and physical properties are compared to ceramics obtained by conventional solid‐state reactions. We report on controlled precipitation and sol‐gel processes, both of which produce materials with particle sizes smaller than 5 μm. We find that the superconducting properties of the high Tc ceramics are affected by their manner of preparation, such that the transitions are slightly lower in temperature, but sharper, for samples made by solution rather than solid‐state chemistry. The ability to prepare stable viscous gels provides an opportunity for obtaining large areas of superconducting coatings. For thick films on alumina or silicon substrates, contamination from the substrate is shown to be a problem. Finally, we observe that the sol‐gel process lowers the synthesis temperature by 100 °C.

Growth, structural, and physical properties of superconducting Nd2-xCexCuO4 crystals.

Abstract: Single crystals of the n-type Nd-Ce-Cu-O superconducting materials have been grown via a flux technique, and their structural and physical properties characterized. Optimum crystal growth conditions were arrived at from a survey of various compositions and temperatures. We determine that the charge composition (50 mol % ${\mathrm{Nd}}_{2}$${\mathrm{O}}_{3}$--${\mathrm{CeO}}_{2}$, 50 mol % CuO) held at a temperature of 1300 \ifmmode^\circ\else\textdegree\fi{}C and followed by a slow cooling to 1000 \ifmmode^\circ\else\textdegree\fi{}C produces plateletlike crystals of the n-type phase ${\mathrm{Nd}}_{2\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{Ce}}_{\mathrm{x}}$${\mathrm{CuO}}_{4}$, which, after being annealed at 900 \ifmmode^\circ\else\textdegree\fi{}C in nitrogen, become superconducting. The limit of the Ce solubility is x=0.18, and only crystals having a Ce content between 0.14 and 0.17 were found to superconductors, with the maximum ${T}_{c}$ occurring at x=0.14. The oxygen uptake and loss in the Nd material is similar to that measured on ${\mathrm{La}}_{2}$${\mathrm{CuO}}_{4}$ but occurs at higher temperatures (750 \ifmmode^\circ\else\textdegree\fi{}C instead of 500 \ifmmode^\circ\else\textdegree\fi{}C). The large Meissner fraction indicates bulk superconductivity. However, due to a complex microstructure or compositional (e.g., oxygen) inhomogeneities in the crystal, zero resistance is difficult to achieve. The resistivity temperature dependence above ${T}_{c}$ is metalliclike, and linear above 150 K, in contrast to bulk ceramics. Finally, no evidence for magnetic ordering over the temperature range 4--350 K was observed for the superconducting Ce-doped ${\mathrm{Nd}}_{2}$${\mathrm{CuO}}_{4}$ phase, whereas signs of magnetic ordering were found at 340 K for the undoped material.

Angle-resolved photoemission studies of the cuprate superconductors

Abstract: The last decade witnessed significant progress in angle-resolved photoemission spectroscopy (ARPES) and its applications. Today, ARPES experiments with 2-meV energy resolution and $0.2\ifmmode^\circ\else\textdegree\fi{}$ angular resolution are a reality even for photoemission on solids. These technological advances and the improved sample quality have enabled ARPES to emerge as a leading tool in the investigation of the high-${T}_{c}$ superconductors. This paper reviews the most recent ARPES results on the cuprate superconductors and their insulating parent and sister compounds, with the purpose of providing an updated summary of the extensive literature. The low-energy excitations are discussed with emphasis on some of the most relevant issues, such as the Fermi surface and remnant Fermi surface, the superconducting gap, the pseudogap and $d$-wave-like dispersion, evidence of electronic inhomogeneity and nanoscale phase separation, the emergence of coherent quasiparticles through the superconducting transition, and many-body effects in the one-particle spectral function due to the interaction of the charge with magnetic and/or lattice degrees of freedom. Given the dynamic nature of the field, we chose to focus mainly on reviewing the experimental data, as on the experimental side a general consensus has been reached, whereas interpretations and related theoretical models can vary significantly. The first part of the paper introduces photoemission spectroscopy in the context of strongly interacting systems, along with an update on the state-of-the-art instrumentation. The second part provides an overview of the scientific issues relevant to the investigation of the low-energy electronic structure by ARPES. The rest of the paper is devoted to the experimental results from the cuprates, and the discussion is organized along conceptual lines: normal-state electronic structure, interlayer interaction, superconducting gap, coherent superconducting peak, pseudogap, electron self-energy, and collective modes. Within each topic, ARPES data from the various copper oxides are presented.

Electronic structure of the high-temperature oxide superconductors

Abstract: Since the discovery of superconductivity above 30 K by Bednorz and M\"uller in the La copper oxide system, the critical temperature has been raised to 90 K in Y${\mathrm{Ba}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7}$ and to 110 and 125 K in Bi-based and Tl-based copper oxides, respectively. In the two years since this Nobel-prize-winning discovery, a large number of electronic structure calculations have been carried out as a first step in understanding the electronic properties of these materials. In this paper these calculations (mostly of the density-functional type) are gathered and reviewed, and their results are compared with the relevant experimental data. The picture that emerges is one in which the important electronic states are dominated by the copper $d$ and oxygen $p$ orbitals, with strong hybridization between them. Photon, electron, and positron spectroscopies provide important information about the electronic states, and comparison with electronic structure calculations indicates that, while many features can be interpreted in terms of existing calculations, self-energy corrections ("correlations") are important for a more detailed understanding. The antiferromagnetism that occurs in some regions of the phase diagram poses a particularly challenging problem for any detailed theory. The study of structural stability, lattice dynamics, and electron-phonon coupling in the copper oxides is also discussed. Finally, a brief review is given of the attempts so far to identify interaction constants appropriate for a model Hamiltonian treatment of many-body interactions in these materials.

Invited review “sol-gel” preparation of high temperature superconducting oxides

Abstract: This review article focuses on the sol-gel preparation of high temperature superconducting oxides wherein different classes of gel technologies were utilized. These involve: 1) the sol-gel route based upon hydrolysis-condensation of metal-alkoxides, 2) the gelation route based upon concentration of aqueous solutions involving metal-chelates, often called as “chelate gel” or “amorphous chelate” route, and 3) the organic polymeric gel route. This paper reviews the current status of these sol-gel processes, and illustrates the underlying chemistry involved in each sol-gel technology. It is demonstrated that the chemical homogeneity of the gel is often disturbed by the differences in the chemistries of the cations. Prior to gelation the starting precursor solution containing various forms of metal-complexes must be chemically modified to overcome this problem. Illustration of a variety of strategies for success in obtaining a homogeneous multicomponent gel with no precipitation is focal point of this review article.

Frustrated electronic phase separation and high-temperature superconductors

Abstract: There is a strong tendency for dilute holes in an antiferromagnet to phase separate. (This is a generic feature of doping into a commensurate correlated insulating state.) We review the general and model-specific theoretical arguments that support this conclusion for neutral holes. In the presence of long-range Coulomb interactions, there is frustrated phase separation leading to large-amplitude, low-energy fluctuations in the hole density at intermediate length scales, provided the dielectric constant is sufficiently large. We describe extensive experimental evidence showing that such “clumping” of the holes is an important feature of the cuprate superconductors. We also summarize theoretical results which suggest that frustrated phase separation may account for the anomalous properties of the normal state and give rise to high-temperature superconductivity.