THERMAL-CONDUCTIVITY OF PURE OR IRON-DOPED YBA2CU3O7-DELTA WITH OR WITHOUT AN EXCESS OF CUO

The thermal conductivities of YBa2(Cu1-xFex)3O7-delta + y% CuO ceramics for 0 < x < 0.03 and 0 < y < 5 have been measured. The thermal conductivities of all samples exhibit a minimum in the vicinity of the critical temperature T(c) and a maximum near T(c)/2. These results are interpreted with the help of an electronic model, i.e. supposing that the main contribution to the thermal conductivity below T(c) is due to electron scattering in the CuO2 planes. Within a simple two-fluid model derived from kinetic theory, taking into account the temperature dependence of the electronic relaxation time and the normal charge carrier concentration, we obtain theoretical curves which reproduce the experimental results quite well. We also take into account the porosity of the samples (in term of an intergrain contribution) to derive the electronic thermal conductivity. The parameter values of the model and the observed minimum are explained in terms of physical properties. In particular, the contribution of superconductivity fluctuations to the thermal conductivity is shown to be negligible with respect to other mechanisms.