Preferred Orientation Contribution to the Anisotropic Normal State Resistivity in Superconducting Melt-Cast Processed Bi2Sr2CaCu2O8+δ

Abstract

We describe how the contribution of crystallographic texture to the anisotropy of the resistivity of polycrystalline samples can be estimated by averaging over crystallographic orientations through a geometric mean approach. The calculation takes into account the orientation distribution refined from neutron diffraction data and literature values for the single crystal resistivity tensor. The example discussed here is a melt-cast processed Bi2Sr2CaCu2O8+δ (Bi-2212) polycrystalline tube in which the main texture component is a <010> fiber texture with relatively low texture strength. Experimentally-measured resistivities along the longitudinal, radial, and tangential directions of the Bi-2212 tube were compared to calculated values and found to be of the same order of magnitude. Calculations for this example and additional simulations for various texture strengths and single crystal resistivity anisotropies confirm that in the case of highly anisotropic phases such as Bi-2212, even low texture strengths have a significant effect on the anisotropy of the resistivity in polycrystalline samples.

Anisotropy of the thermal conductivity of bulk melt-cast Bi-2212 superconducting tubes

“…The resistivity values are comparable to those measured along the axis of bulk melt-cast Bi-2212 bars [29]. The anisotropy behavior depicted in figure 3 qualitatively agrees with results obtained on similar samples [21] in that the normal-state resistivity ratio ρ(axial,azimuthal) / ρ(radial) is very weakly temperature dependent with an average value equal to ~ 1.5, which is smaller than the ratio ~ 2.3 found by Dellicour et al [21] for a similar tube of other dimensions (wall thickness ~7.5 mm) and, thus, different solidification microstructure. As found in [21], however, the normal state resistivity normalized at 300 K, ρ(T) / ρ(300 K), is almost independent of the direction of the current (inset of figure 3).…”

“…A <010> fiber texture with the axis parallel to the radial direction was deduced from XRD and neutrondiffraction studies. Though the texture was rather weak, not exceeding seven multiples of a random distribution, its combination with the extremely high intrinsic anisotropy of the Bi-2212 single grains [22] resulted in a noticeable anisotropy of the normal state resistivity, which was found to be a factor of two lower along the radial direction than along both axial and azimuthal directions of the tube [21]. These results agree with the qualitative picture in which the Bi-2212 platelets are preferentially oriented with their c-axes in a plane perpendicular to the radial direction [9].…”

“…The purpose of the present work is to investigate the anisotropy of the thermal conductivity of bulk Bi-2212 tubes fabricated by melt-cast process. This study is also motivated by recent quantitative texture analysis of these polycrystalline materials [21]. A <010> fiber texture with the axis parallel to the radial direction was deduced from XRD and neutrondiffraction studies.…”

In situ x-ray and neutron diffraction investigation of Bi-2212 in multifilamentary wires during thermal treatment

“…(Figure 10). This result is consistent with previous studies carried out on round wires [27] and melt-cast processed polycrystalline tubes of Bi-2212 [28], where a preferred orientation along [100] or [010] was detected by assuming an orthorhombic structural model (in the orthorhombic structural model the a and b axes are rotated by 45° and these lattice parameters are a factor of 2 longer compared with the tetragonal a and b axes). Conversely, it starts to grow only after more than 9 hours (869 °C) in the air treated sample; also in this sample the preferred orientation along [110] is evident, but in this case the remaining diffraction peaks exhibit noticeable intensities, thus indicating a lower degree of textur-ing.…”

Quantitative phase analysis of Bi2Sr2CaCu2O8+x and competing intergrowth and co-crystallizing phases via a Rietveld refinement study

“…Rietveld refinement with incorporation of the structure alone did not give a very good fit and there is a large deviation of the intensity from the theoretically calculated intensities. The Bi-2212 system suffers from preferred orientation along the {00l} direction (Schmahl et al, 1998;Dellicour et al, 2017;Zhao et al, 1995;Rajak et al, 2018). This effect is expected to be enhanced in our powders since they were obtained by grinding a large number of single crystals and hence are expected to be textured.…”