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

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 kappa(T) along the axial and azimuthal directions are found to be equal within experimental uncertainty, while kappa along the radial direction is found to be ~ 40% larger than the other two. The results are in qualitative agreement with the weak partial texture of such tubes, corresponding also to an anisotropy of the resistivity rho(T) above the critical temperature Tc. This resistivity anisotropy in the normal state is responsible for an anisotropy of the electronic contribution of thermal conductivity (delta_kappa_e), which is much smaller than the anisotropy delta_kappa 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 Tc. 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 the thermal conductivity into account, e.g. for predicting the self-heating when the material is subjected to losses.