Magnetic and structural properties ofYBa2Cu3O

Abstract

YBazCu30z -F&, y 0.08 to 1.11, has been prepared by annealing YBazCu30z "(1:2:3)in NF3 gas. X-ray and neutron-diffraction studies show that the fluorine is structurally incorporated into the CuO chains, in the normally vacant O(5) sites along the a axis. Structurally, this results in a decrease in the orthorhombic strain (h -a)l(b+a). This material exhibits significant increases in diamagnetic expulsion and exclusion as a function of fluorine content, but no increase in T,. At sufficiently long anneal times (large y) the material undergoes an orthorhombic-totetragonal phase transition, and no longer superconducts.An amorphous phase also appears.These results tie together the various conflicting reports of fluorination of 1:2:3.

Phase diagrams for the YBa2Cu3O7 family — ANNO 1996

“…Chlorine and bromine, on the other hand, would only enter the vacancies inside the chains. This is in accordance with structural data from PND [597,602].…”

“…It is experimentally well established that fluorine [597,600,601], chlorine and even bromine [602] enter the vacant oxygen sites in the Cu(1) coordination sphere, in concentrations decreasing in the said order. Quantum-chemical calculation [602] of the alternative structures for the thus formed halogenide cuprate anions show that upon the reaction with the molecular halogens only the vacant oxygen sites are reasonable candidates for accommodation of the halogen atoms.…”

“…Also here the feasible synthesis route is the direct halogenation of YBa2Cu306+w at slightly elevated temperatures, preferably [597] by NF3 in case of fluorine. Attempts to introduce halogens as Ba halogenides into the ceramic syntesis yield no reaction [598,599].…”

On rearrangements of the Haar system in the space BMO

“…After an annealing at 300 • C, these authors only observed an increase of the transition width when the fluorine content was increased. In the same conditions, LaGraff et al [12] did not observe any effect on T c but an increase of the diamagnetic expulsion and exclusion.…”

The Dependence of the Flux Pinning Effects on the Au Mole Fraction in Y1Ba2Cu3-3xAu3xO7-? Superconductors

“…As Au is added to the Y 1 Ba 2 Cu 3± ±3x Au 3x O 7± ±d superconductor, the width of the superconductivity transition increases as a result of the formation of a nonuniform superconductivity phase. The T c , the volume fraction (± ±4pc DS ), and the Meissner effect (c ME /c DS ) for Y 1 Ba 2 Cu 3± ±3x Au 3x O 7± ±d at 10 K for various Au mole fractions are summarized in Table 2 [17]. The magnetization (M) is calculated from the ZFC in Fig.…”