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 ceramic s for 0 < x < 0.03 and 0 < y < 5 have been measured. The thermal condu ctivities of all samples exhibit a minimum in the vicinity of the crit ical temperature T(c) and a maximum near T(c)/2. These results are int erpreted with the help of an electronic model, i.e. supposing that the main contribution to the thermal conductivity below T(c) is due to el ectron scattering in the CuO2 planes. Within a simple two-fluid model derived from kinetic theory, taking into account the temperature depen dence of the electronic relaxation time and the normal charge carrier concentration, we obtain theoretical curves which reproduce the experi mental results quite well. We also take into account the porosity of t he samples (in term of an intergrain contribution) to derive the elect ronic thermal conductivity. The parameter values of the model and the observed minimum are explained in terms of physical properties. In par ticular, the contribution of superconductivity fluctuations to the the rmal conductivity is shown to be negligible with respect to other mech anisms.