Effect of boron doping in the microwave surface resistance of neutron irradiated melt-textured Y(1.6)Ba(2.3)Cu(3.3)O(7-x) samples

We report on the microwave surface resistance of melt-textured Y(1.6)Ba(2.3)Cu(3.3)O(7-x) samples, doped with different amount of B2O3 and, subsequently, irradiated by thermal neutrons at the fluence of 1.476 x 10^17 cm^ 2. The microwave surface resistance has been measured as a function of temperature and DC magnetic field. The experimental results are quantitatively discussed in the framework of the Coffey and Clem theory, properly adapted to take into account the d-wave nature of cuprate superconductors. By fitting the experimental data at zero DC field, we have highlighted the effects of the induced defects in the general properties of the samples, including the intergranular region. The analysis of the results obtained at high DC fields allowed us to investigate the fluxon dynamics and deduce the depinning frequency; in particular, we show that the addition of B(2)O(3) up to 0.1 wt.% increases the effectiveness of the defects to hinder the fluxon motion induced by the microwave current.