Effect of boron doping in the microwave surface resistance of neutron irradiated melt-textured Y_1.6Ba_2.3Cu_3.3O_7-x samples

摘要

We report on the microwave surface resistance of melt-texturedY_1.6Ba_2.3Cu_3.3O_7-x samples, doped with different amount of B_2O_3 and,subsequently, irradiated by thermal neutrons at the fluence of 1.476 \times10^17 cm^-2. The microwave surface resistance has been measured as a functionof temperature and DC magnetic field. The experimental results arequantitatively discussed in the framework of the Coffey and Clem theory,properly adapted to take into account the d-wave nature of cupratesuperconductors. By fitting the experimental data at zero DC field, we havehighlighted the effects of the induced defects in the general properties of thesamples, including the intergranular region. The analysis of the resultsobtained at high DC fields allowed us to investigate the fluxon dynamics anddeduce the depinning frequency; in particular, we have shown that the additionof B_2O_3 up to 0.1 wt% increases the effectiveness of the defects to hinderthe fluxon motion induced by the microwave current.