Observations of twinning in YBa₂Cu₃O_{6  x}, 0 <x< 1, at high temperatures

Abstract

We report here on the nature of the twinning associated with the tetragonal to orthorhombic I (T/OI) phase transition in YBCO, for temperatures between 500 and 600ºC. In situ neutron diffraction measurements show the coexistence of the T and split OI peaks in the vicinity of the transition. However, by direct numerical simulation, we show that this is to be expected from the twinned OI structure when the separation of adjacent twinning planes and the orthorhombicity both approach zero. It is demonstrated that the observed hkl-dependent peak broadening is consistent with this interpretation. A comparison of the measured and simulated peak shapes enables us to make an approximate estimate of the actual twin widths for a given orthorhombicity.

Superconducting properties of the Sr substituted La3Ca1−xSrxBa3Cu7Oysystem

“…The standard Rietveld technique was used for the analysis of the XRD data. The structural analysis reveals a tetragonal triple perovskite structure with the P4/mmm space group without a transition to the orthorhombic structure, as is observed for the Y-123 superconductor [11], for all samples. The lattice parameters which were obtained by fitting the experimental XRD data using the standard Rietveld technique versus the doping level x are plotted in figure 2.…”

“…The substitute of Fe, Co, Ni, Zn, etc, for Cu reduces the T c of Y-123 [7][8][9], while rare-earth substitution for Y has little influence on the superconductivity [10]. It is well known that the high-T c superconducting oxides R-123 (R is a rare-earth element) undergo an orthorhombic to tetragonal transition as a result of a variation in the oxygen content [11], and the oxygen content also affects the T c values, which has made their use in technological applications difficult. As compared with R-123, there was no tetragonal to orthorhombic phase transition in La-3137.…”

Coherence effects in the scattering from domain structures

“…Surprisingly, in spite of the fact that the diffraction theory is well known, the inherent interference effects seem to have been overlooked or ignored in many interpretations of experimental data. This has recently been demonstrated again by Khoshnevisan et al (2002) in a study of the tetragonal to orthorhombic phase transition in YBCO by powder diffraction methods. By analytical and simulation studies they found that for specific values of the domain sizes (lateral extension) and strains, additional peaks between twin-related reflection pairs can show up, which may be misinterpreted as arising from the high-symmetry structure, which is in fact not present in the sample as a separate phase.…”

Structural Changes in YBa2Cu3O7 Thin Films Modified with He+-Focused Ion Beam for High-Temperature Superconductive Nanoelectronics

“…The in-plane a and b lattice parameters were determined from φ-scan and θ – 2θ scans of the twinned peaks 403/043 (Supporting Information, Figure S2). The ⟨110⟩ twinning appears due to a small difference between the in-plane lattice parameters a and b , − which leads to the spitting Δ­(2θ) in the direction of the scattering angle and also to the angular separation of the 403/043 peaks by Δφ = 90° – 2 arctan­( a / b ). This allowed us to determine the symmetry of the YBCO lattice and the values of all three lattice parameters as a function of the ion dose (Figure b,c).…”