Oxygen Deficiency and Cu Valence States of Superconducting Y-Ba-Cu Oxide

Abstract

D b r i e m e n t d'ktrophysique Relativiste et d e Cosmologie O b m t o i r e , 92190 Meudon, France AbsImacL Slatting from the equations of motion obeyed by fields, as they result from general approximations [they are m!ia to be of the following form [k2n(k)]+ = 0, for quasi bosons, and a similar equation for quasifermions] a lagmgian formalism is derived and, accordingly, consewed quantities are obtained. Next these fields are quantized and general expressions for the main observables are derived. Statistical mechanics of quasiparlicles then follow via the use of covariant Wigner functions.

Characterization of the Local Layer Structure of a Narrow Wall in a Surface Stabilized Ferroelectric Liquid Crystal Using Synchrotron X-Ray Micro-Diffraction

“…93 K and 92 K respectively. The roomtemperature resistances for the oxygen-annealed and furnacecooled samples are 1.35 m and 3.6 m respectively, these results are in agreement with the previous studies [11]. Figure 2 shows the temperature dependence of the resistance for air-quenched…”

“…We note that when x = 0.0 zero resistance was not achieved down to 72 K, although an onset drop in the resistance was observed around 90 K, which agrees with the previous findings that oxygen annealing or slow cooling in air is a prerequisite for obtaining a 90 K phase of YBa 2 Cu 3 O 7−δ [11]. The highest T c (zero) was observed at 90 K when x = 0.02; further increases in the concentration of Sb decreased the zero-resistance temperature.…”

“…YBa 2 Cu 3 O 7−δ crystallizes in the orthorhombic or tetragonal forms depending on the synthesis conditions [1][2][3][4][5][6][7][8][9]. It is well known that the crystal structure and the superconducting properties are strongly interlinked with each other, and depend on the oxygen content [9,10] and the ratio of Cu II and Cu III [11]. To achieve the orthorhombic structure oxygen annealing or slow cooling in air is required [5,6,11]; whereas annealing in argon, nitrogen or rapid cooling (quenching) results in the stabilizing of the tetragonal structure [2][3][4].…”

“…It is well known that the crystal structure and the superconducting properties are strongly interlinked with each other, and depend on the oxygen content [9,10] and the ratio of Cu II and Cu III [11]. To achieve the orthorhombic structure oxygen annealing or slow cooling in air is required [5,6,11]; whereas annealing in argon, nitrogen or rapid cooling (quenching) results in the stabilizing of the tetragonal structure [2][3][4]. From these studies it has been established that for superconductivity of about 90 K materials should have an orthorhombic symmetry.…”

Synthesis and characterization of YBa2Cu3-xSbxO7-δhigh-temperature superconductors

“…YBa 2 Cu 3 O 7−δ crystallizes in the orthorhombic or tetragonal forms depending on the synthesis conditions [1][2][3][4][5][6][7][8][9]. It is well known that the crystal structure and the superconducting properties are strongly interlinked with each other, and depend on the oxygen content [9,10] and the ratio of Cu II and Cu III [11]. To achieve the orthorhombic structure oxygen annealing or slow cooling in air is required [5,6,11]; whereas annealing in argon, nitrogen or rapid cooling (quenching) results in the stabilizing of the tetragonal structure [2][3][4].…”