Rare-earth Barium Copper Oxide Research Articles

Improved microstructure and enhanced low-fieldJc in(Y0.67Eu0.33)Ba2Cu3O7−δ films

This paper reports a study on mixed rare-earth barium–copper oxide superconducting films(Y0.67Eu0.33)Ba2Cu3O7−δ of different thicknesses grown on single-crystalSrTiO3 substrates by pulsed laser deposition (PLD). X-ray diffraction (XRD), scanning electronmicroscopy (SEM) and cross-sectional transmission electron microscopy (TEM) were employedto investigate film crystallinity, surface morphology and microstructure. Critical currentdensity in self-field as a function of film thickness and in an applied magnetic field as afunction of field strength and direction were also measured. The results show high quality(Y0.67Eu0.33)Ba2Cu3O7−δ films with a smoother and denser surface morphology compared to that of pureYBa2Cu3O7−δ. A thickness-dependent self-field critical current density quantitatively similar to that of pureYBa2Cu3O7−δ was observed, which suggests that the microstructural evolution in terms ofincreasing surface roughness and microporosity as well as crystallinity degradationis not likely to be playing a critical role in the form of the dependence.(Y0.67Eu0.33)Ba2Cu3O7−δ films also exhibit improved magnetic field performance at low fields over a wide range oforientations in the intermediate angle region, indicating that probable additional randompinning sites were introduced by the substitution of europium in one-third of yttrium sites.

Comment on “Implications of Abrikosov-Gor'kov exchange scattering for theories of high temperature superconductivity” by Blackstead and Dow

Experimental data do not support pair breaking as the primary mechanism for the depression of superconducting transition temperature in rare-earth barium copper oxides doped with magnetic rare-earth ions as asserted by Blackstead and Dow [Phys. Lett. A 206 (1995) 107]. Thus the case for locating mobile charges outside the copper oxide planes is not compelling.

Electric-field gradient at oxygen sites in RBCO: Effects from a positive muon

A limited quantum chemistry approach has been used to examine changes to the electric-field gradient at oxygen sites in rare-earth barium copper oxides (RBCO) due to a bonded muon (or hydrogen). Results are reported for an all electron, extended basis set calculation for an OMu− molecule which is embedded in various point charge clusters to simulate the RBCO crystal environment. Differences between the gradients for O2− and OMu− are examined for five likely muon bond sites. In each case the muon significantly modifies the calculated gradient.

Sharp optical lines in rare-earth barium copper oxides.

We report the results of a sensitive technique of optical spectroscopy applied to bulk and thin-film samples of the high-{Tc} superconductor {ital R}Ba{sub 2}Cu{sub 3}O{sub 7{minus}{ital x}} with {ital R}=Er, Ho, and Yb. Sharp crystal electric field lines were observed in these samples at 77 and 4.2 K due to impurities of less than 1% of the so-called green phase,'' {ital R}{sub 2}BaCuO{sub 5}. Expected strong magnetic dipole transitions in the superconductor were not observed, probably because of strain broadening of the energy levels involved. The method can reveal absorption lines corresponding to oscillator strengths of 10{sup {minus}10}, for expected linewidths, in opaque or thin-film samples.

Compounds in mixed phase CeBa2Cu3Oy and TbBa2Cu3Oy systems

An analysis of the composition of Ce and Tb barium copper oxide samples with the nominal composition CeBa2Cu3Oy and TbBa2Cu3Oy, prepared with the same solid state reaction method used for the other superconducting rare earth (R) barium copper oxide RBa2Cu3O7-δ compounds, is described. The analysis indicates that these samples are multiphase and consist mostly of 1) the perovskite phases BaCeO3 or BaTbO3, 2) CuO, and 3) BaCuO2. No trace of the oxygen deficient orthorhombic perovskite type structure of YBa2Cu3O7-δ could be found in the X-ray diffraction patterns. Consequently, the compounds do not display superconductivity. The magnetization measurements indicate that BaCeO3 is weakly paramagnetic which is consistent with tetravalent Ce. The BaTbO3 compound exhibits an antiferromagnetic transition at a Neel temperature TN-35 K, and its magnetic susceptibility above TN can be described by a Curie-Weiss law with an effective moment that corresponds to tetravalent Tb.

Superconducting transitions of the (Yb,Lu,Sc)Ba2Cu3O7−y systems

In the rare earth barium copper oxide system RBa 2 Cu 3 O 7-y , almost all compounds show superconductivity above 90 K (R = Y, La, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, Lu, Th) (1–10). However, no YBa 2 Cu 3 O 7 -type phase or superconductivity was observed in ScBa 2 Cu 3 O 7 (11,12). Whether this is due to smaller ionic radius of the Sc 3+ ion (0.73 A) or difficult sample preparation condition is not clear. In order to check these possibilities, we study two pseudoquaternary systems (Yb 1−x Sc x ) Ba 2 Cu 3 O 7−y and (Lu 1−x Sc x )Ba 2 Cu 3 O 7−y where ionic radii of Yb 3+ (0.86 A) and Lu 3+ (0.85 A) are closer to Sc 3+ ion. Superconducting properties of these two systems from electrical and magnetic measurements as well as crystallographic properties will be discussed in detail.