GRAIN-BOUNDARIES CONTRIBUTION TO THE COMPLEX SUSCEPTIBILITY OF KCU-DOPED YBCO HIGH-TEMPERATURE SUPERCONDUCTORS

We present results concerning the effect of adding potassium and exces s copper (1 divided by 5 wt.%) to the initial powder Y(1-0.2x)Ba(2-0.2 x)KxCu3Oy, (x = 0 divided by 0.95) on the a.c. complex susceptibility and the development of the microstructure within the YBCO high-tempera ture superconducting system. The a.c. complex susceptibility chi(ac) = chi'-j chi '' of KCu-doped YBCO was measured as a function of the tem perature, the magnetic field amplitude and the KCu concentration. The behavior of the intergrain loss temperature T-m was analyzed through t he relationship h = a(1 - t)''. The results obtained showed that the p resence of K3CuO2 on the grain boundaries changes drastically the inte rgranular coupling and, within certain concentration limits, improves the critical HTSC characteristics.