INTERGRANULAR ACTIVATION-ENERGIES IN YBA2CU3O7 BULK SUPERCONDUCTORS

Ac susceptibility is used to measure a small shift of the coupling pea k of the imaginary part of the ac susceptibility (chi'') to a higher t emperature as the frequency is increased. Applying the Bean model one obtains the zero-field and zero-temperature intergranular pinning pote ntial U(0,0) and the critical, integranular current density J(c)(0,0) from the data. Here it is shown how one can calculate the intergranula r flux creep activation energy E(a)(T,H) as a function of the applied magnetic field H and the temperature T if the average grain radium R(g ) and the zero temperature London penetration depth lambda(L)(0) are k nown. We arrive at E(a)(T,H) values between 0 and 26 meV for a range o f temperatures between 0 and T(c) and a range of ac fields between 0 a nd 20 Oe.