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

Abstract

We investigate experimentally the anisotropy of the temperature dependence of the thermal conductivity of bulk Bi₂Sr₂CaCu₂O₈ (Bi-2212) cylinders fabricated by the melt-cast process. The thermal conductivity κ(T) along the axial and azimuthal directions are found to be equal within experimental uncertainty, while κ along the radial direction is found to be ~ 40% larger than the other two. The results are in qualitative agreement with the weak texture of such tubes, corresponding also to an anisotropy of the resistivity ρ(T) above the critical temperature T_c. This resistivity anisotropy in the normal state is responsible for an anisotropy of the electronic contribution of thermal conductivity (Δκ_e), which is much smaller than the anisotropy Δκ of the total thermal conductivity. This indicates an anisotropic contribution of the phonons. The temperature dependence of the specific heat C(T) is also measured and shows that C(T)/T exhibits a well-defined maximum close to T_c. The combination of these experimental data can be used for assessing the thermal effects in bulk melt-cast Bi-2212, and underline the importance of taking the anisotropy of κ into account, e.g. for predicting the self-heating when the material is subjected to losses.