Time evolution of the magnetic properties of La0.5R0.5Ba2Cu3O6+x (R = rareearth) high-T-c superconductors

The magnetic properties of the mixed high-T-c superconductors La0.5R0.5Ba2C u3O6+3 (R - rare earth)are studied after prolonged 'aging' at room temperat ure (RT) for 1 year. Enhancement of the superconducting properties comprisi ng the increase of the inhomogeneous diamagnetic signal for members of the series with the larger R-ion radius is detected after RT 'aging'. For the m embers with the larger R-ion radius the diamagnetic signal has been come mo re stronger whereas for the members with the smaller R-ion radius the time evolution of the superconducting properties remained almost the unchanged a nd the diamagnetic signal slightly decreases after 'aging'. The growth of t he EPR intensity of localized Cu2+ centers complying with the rise of the n ormal-state magnetic susceptibility after prolonged storage at RT, is detec ted. The time evolution effects are related to slow ion diffusion processes that can be induced by stress-relaxation in the mixed La0.5R0.5Ba2Cu3O6+x structure, most pronounced for large R-ion radius. (C) 1999 Elsevier Scienc e B.V. All rights reserved.