NONEQUILIBRIUM EFFECTS IN THE THERMAL-CONDUCTIVITY OF BI-BASED HIGH-TEMPERATURE SUPERCONDUCTORS

Thermal conductivity of two Bi-based high temperature superconducting ceramics, 2212 and 2223, with a markedly different microstructure have been examined. A pulse technique has been used. Depending on the heating pulse duration, the more weak-links-containing 2223 sample shows either equilibrium or nonequilibrium behavior. The temperature dependence of the thermal conductivity between 110 K and 180 K is found to obey the Arrhenius law. The experimental observations are interpreted as a thermally activated heat flux motion through the polycrystalline grain boundaries with an energy barrier of nearly 10meV. It is likely due to a phase slip mechanism. An extra relaxation process due to the pore content/structure is thus emphasized in such regimes.