K. Sreedhar

Bio: K. Sreedhar is an academic researcher from Indian Institute of Science. The author has contributed to research in topics: High-temperature superconductivity & Superconductivity. The author has an hindex of 7, co-authored 10 publications receiving 230 citations.

Identification of the phase responsible for high-temperature superconductivity in $Y-Ba-Cu$ oxides

Abstract: The discovery of La–Ba(Sr)–Cu oxides of K2NiF4 structure exhibiting superconductivity in the 30–40 K region was reported early this year1. The recent announcement of superconductivity above the temperature of liquid nitrogen in Y–Ba–Cu oxides2 has belied all expectations. Unfortunately, all the Y–Ba–Cu oxide compositions exhibiting this remarkable feature were biphasic or multiphasic. We have studied various compositions of the Y3–xBa3+xCu6O14 and now report the isolation of the pure oxide phase responsible for high Tc superconductivity. This oxide has the composition Y0.33Ba0.67CuO2.33±δ, with an oxygen defect perovskite structure. The pure oxide shows the onset of superconductivity at 120 K, attaining zero resistance at 87 K. It also exhibits the highest Meissner effect of all the high-Tc oxide superconductors.

Identification of the high-temperature superconducting phase in the Y-Ba-Cu-O system as the perovskite YBa 2 Cu 3 O 7 ±δ

Abstract: The oxide responsible for high-temperature superconductivity (onset ∼100 K, zero resistance above liquid N2 temperature) is found to be YBa2Cu3O7±δ.

High-temperature superconductivity in the 100 K region in perovskite-related oxides of the Ln-Ba-Cu-O (Ln=Y or La) system

Abstract: Oxides of the Y-Ba-Cu-O system are found to show onset of superconductivity in the 100–120 K region.

Structure and Reactivity of Perovskite-Type Oxides

Abstract: Publisher Summary This chapter discusses the structure and reactivity of perovskite-type oxides. Perovskite-type oxides have the general formula ABO 3 (A, cation of larger size) and are structurally similar to CaTiO 3 , the mineral that gave its name to that group of compounds. These materials are first studied because of their important physical properties such as ferro-, piezo-, and pyroelectricity, magnetism and electrooptic effects. The most numerous and most interesting compounds with the perovskite structure are oxides. Some hydrides, carbides, halides, and nitrides also crystallize with this structure. The chapter reviews only the study of oxides and their behavior in the gas solid interface and in heterogeneous catalysis. An important characteristic of perovskites, mentioned in the chapter, is their susceptibility of partial substitution in both A and B positions. This provides a wealth of isomorphic compounds that can easily be synthesized. Given the extensive range of possibilities in the tailoring of their chemical and physical properties, there is no doubt that new reactions can be studied, where these oxides can participate as catalytic agents.

Identification of the phase responsible for high-temperature superconductivity in $Y-Ba-Cu$ oxides

Abstract: The discovery of La–Ba(Sr)–Cu oxides of K2NiF4 structure exhibiting superconductivity in the 30–40 K region was reported early this year1. The recent announcement of superconductivity above the temperature of liquid nitrogen in Y–Ba–Cu oxides2 has belied all expectations. Unfortunately, all the Y–Ba–Cu oxide compositions exhibiting this remarkable feature were biphasic or multiphasic. We have studied various compositions of the Y3–xBa3+xCu6O14 and now report the isolation of the pure oxide phase responsible for high Tc superconductivity. This oxide has the composition Y0.33Ba0.67CuO2.33±δ, with an oxygen defect perovskite structure. The pure oxide shows the onset of superconductivity at 120 K, attaining zero resistance at 87 K. It also exhibits the highest Meissner effect of all the high-Tc oxide superconductors.

Absorption of electromagnetic radiation by superconducting YBa2Cu3O7: an oxygen-induced phenomenon

Abstract: In the superconducting state, YBa2Cu3O7 absorbs electromagnetic radiation over a wide range of frequencies (8 MHz-9 GHz). The absorption is extremely sensitive to temperature, particle size and the magnetic field and depends crucially on the presence of oxygen. A possible explanation for the phenomenon based on the formation of Josephson junctions is suggested.

The Structure of Y1Ba2Cu3O7-δ and its Derivatives

Abstract: 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.