Intergranular activation energies in YBa2Cu3O7 bulk superconductors

Ac susceptibility is used to measure a small shift of the coupling peak of the imaginary part of the ac susceptibility (χ'') to a higher temperature as the frequency is increased. Applying the Bean model one obtains the zero-field and zero-temperature intergranular pinning potential U(0,0) and the critical, integranular current density Jc(0,0) from the data. Here it is shown how one can calculate the intergranular flux creep activation energy Ea(T,H) as a function of the applied magnetic field H and the temperature T if the average grain radius Rg and the zero temperature London penetration depth λL(0) are known. We arrive at Ea(T,H) values between 0 and 26 meV for a range of temperatures between 0 and Tc and a range of ac fields between 0 and 20 Oe. (orig.)