Publisher Summary This chapter discusses the structural studies performed on superconducting oxides. It focuses primarily on Y 1 Ba 2 Cu 3 O 7–δ , nicknamed the 123 structure, because this structure has been the most extensively studied to date. The chapter describes the basic atomic arrangements in Y 1 Ba 2 Cu 3 O 7–δ and the way these arrangements change as a function of processing. The defects that are commonly found in the 123 structure are discussed, some of which play a dominant role in controlling superconducting properties. The studies of elemental substitutions for Y, Ba, Cu and/or O in 123 are summarized, and 123 with the other families of superconducting oxides is compared. These studies have both theoretical and practical interest because they provide clues to the roles that various structural features play in the mechanism of high-temperature superconductivity, which, in turn, may aid in the discovery of even higher temperature superconductors. It is evident from the variety of behaviors exhibited by 123 after different processing conditions that the structure has considerable flexibility. The oxygen stoichiometry can be varied over a wide range, and different cations can be substituted at least partially into every site.

The Structure of Y1Ba2Cu3O7-δ and its Derivatives

Polysaccharides are renewable biodegradable natural materials and are accounted for to control the formation of hybrid silica nanocomposites by sol gel process. The synthesis of templated silica xerogel essentially includes two critical steps of hydrolysis and polycondensation reaction that are started by catalyst and silica precursor solution. Aside from this Saponification guar-graft-polyacrylonitrile (s-GG-g-PAN) as a copolymer are included in the precursor solution for providing a novel templating environment for silica matrix formation. The s-GG-g-PAN acts as a template for the silica produced in the blended framework because of the hydrogen bonding between the hydroxyl groups at silanols and hydroxyl group and carbonyl groups at the copolymer surface. Connected silanol groups can further hydrolyze and after that take part in the condensation reaction. Accordingly, the s-GG-g-PAN template gets trapped inside the resulting silica system, which on calcining at 900 °C is lost, producing pores of shape and size of the template. The surface area and pore volume of the developed templated silica xerogel have been determined. The surface area and pore volume of the template silica xerogel (H900) were observed to be (240 m2 g−1) and (0.286 ccg−1) respectively. The conditions for the adsorption by adsorbent had been enhanced, and kinetics and thermodynamic studies were performed. The best result in terms of lead adsorption was obtained with templated silica xerogel calcined at 900 °C. The % Pb2+ removal is observed to be 96% when H900 adsorbent was treated under ideal adsorption states of measurements 0.05g dose, 500mgL−1 Pb2+ concentration, time 2 h, pH 5 at 30 °C. The adsorption information fitted satisfactorily to Langmuir isotherms, showing unilayer adsorption. In view of the Langmuir model, Qmax was calculated to be 2000 mgg−1. Theadsorption demonstrated pseudo-second-order kinetics. The thermodynamic study revealed the endothermic and spontaneous nature of the adsorption. The adsorbent demonstrated good thermal stability and high reusability. The present study highlights the possibility of silica xerogel derived from saponified guar gum-grafted poly (acrylonitrile) toward its potential application as superior adsorbent for removal of Pb2+ from aqueous solution.

https://link.springer.com/content/pdf/10.1186%2Fs40543-016-0103-8.pdf

Guar gum-grafted poly(acrylonitrile)-templated silica xerogel: nanoengineered material for lead ion removal

The extraction of engineering properties of pavement layers by dynamic analysis of falling weight deflectometer (FWD) data is demonstrated. FWD data from two in-service highway sections were analyzed. The FWD data consist of time records of surface loading and surface deflections at a range of distances. A Texas Transportation Institute pavement dynamics computer program, SCALPOT, was used to generate predicted responses. Physical properties of the pavement were generated by a trial-and-error backcalculation and a Systems Identification computer program. The pavement surface vertical deflections were characterized by using frequency response functions in the form of magnitude and phase angle plots as a function of frequency. The magnitude plots represent vertical pavement surface deformations resulting from a steady-state sinusoidal surface loading. The phase angle data represent the lag angle between the loading and the surface deflections. The asphaltic concrete surface layer was represented as a three-parameter viscoelastic medium. The base course, subgrade layers, and bedrock layers, if any, were treated as damped elastic solids. These physical properties were backcalculated by matching approximately the frequency-analyzed field data with computed values by varying the SCALPOT input data set. Good agreement between experimental and computer-predicted responses was obtained using the backcalculated pavement layer properties. One site with near-surface bedrock was analyzed and good agreement was obtained.

Comparison of computer predictions and field data for dynamic analysis of falling weight deflectometer data

Constant stoichiometry cooling of YBa2Cu3Ox

On passe en revue diverses theories de polarisation dielectrique incluant les anciens modeles dus a Clausius-Mossotti et Mott-Littleton qui conduisent a des relations entre constantes dielectriques et polarisabilites. L'effet de recouvrement des ions voisins sur ces deux grandeurs est discute en termes de potentiels a plusieurs corps de Lowdin-Lundqvist

Dielectric Constants and Their Pressure and Temperature Derivatives for Ionic Crystals

The positron annihilation technique has been used for studying the high-Tc-superconductor YBa2Cu3O7-x. The Doppler broadening lineshape parameter as a function of temperature between 75 and 300 K, and the positron lifetimes of the normal state and of the superconducting state have been measured. A sharp negative anomaly in the S-parameter was observed near the superconducting transition temperature. In addition, it was found that the S-parameter and mean lifetime decrease below the transition temperature Tc. These phenomena vanish for the samples annealed in vacuum at 800 degrees C. It is suggested that high-Tc superconductivity in the new oxide is probably accompanied by an adjustment in the positions of the oxygen vacancies and the occurrence of 'valence pairs', i.e. an enhancement of the covalent character of the electrons after the superconducting transition.

The positron-annihilation anomaly near the superconducting transition-temperature in single-phase yba2cu3o7-x compounds

Phase transitions of Y1Ba2Cu3O9-x compounds and influencing factors have been studied using an X-ray diffractometer equipped with a high-temperature stage. The results showed that there exist three zones of phase transition from room temperature to 1000 degrees C in the compounds. From 400 to 600 degrees C, the transition from orthorhombic to tetragonal phases occurs accompanied by an oxygen release process. Above 950 degrees C, the tetragonal phase is transformed into another high-temperature phase.

https://iopscience.iop.org/article/10.1088/0022-3719/20/23/005/pdf

Phase-transitions in y1ba2cu3o9-x superconductors

Quenching rates corresponding to both different wheel speeds and different materials during the forming process of amorphous ribbons have been measured directly by an infrared thermal photography technique. The results show that this technique is applicable to the measurement of rapid quenching rates. The critical cooling rates are also determined.

Quenching rate measurement in amorphous alloy formation

The authors report the effects of distortions of crystal lattices on the superconductivity of Y-Ba-Cu-O system compounds under different treatment conditions (cooling rates and aging atmosphere). The results show that with an increase of cooling rate the intensities of three dominant X-ray diffraction peaks in the orthorhombic perovskite phase gradually become inverted, which corresponds to the changes in the superconductivity. It has been found that there exists an intense interaction between Y-Ba-Cu-O compounds and polarisable molecules. The interaction may result in the distortion of crystal structure; therefore the superconductivity vanishes in the range above liquid nitrogen temperature. This suggests that there is a close relationship between the distortion of the crystal structure and the superconductivity of the compounds. Based on the experimental data, a quantitative calculation is obtained. The qualitative explanation is suggested based on polarisation theory and crystal-field theory.

The effects of distortions of crystal lattices on superconductivity in the y-ba-cu-o system

Crystal structures or exposure to polarisable environments determined the superconductivity in the Y-Ba-Cu-O system Based on the sequence of broken symmetry and lattice distortions in perovskite structures, quasi-ferroelectricity (QF) is considered to play an important role in the new superconductive oxide compounds The authors suggest an idea for seeking higher-Tc superconductive systems

Yang Zhongjin

Papers

The positron-annihilation anomaly near the superconducting transition-temperature in single-phase yba2cu3o7-x compounds

Phase-transitions in y1ba2cu3o9-x superconductors

Quenching rate measurement in amorphous alloy formation

The effects of distortions of crystal lattices on superconductivity in the y-ba-cu-o system

Ferroelectricity in high-Tc superconductors