Harmonic susceptibilities of polycrystalline (La1-xCax)(Ba1.75-xLa0.25+x)Cu3O7+d synthesized by amorphous metal-complex method

Single-phase tetragonal (La1-xCax)(Ba1.75-xLa0.25+x)Cu3O7+d polycrystals with the composition range 0.1 less than or equal to x less than or equal to 1.0 were synthesized by the amorphous metal-complex method, The fundamental and the higher-harmonic complex susceptibilities chi(n) = chi(n)(') - ichi(n)(n) (n = 1, 2, 3, 5, and 7) were measured by means of Hartshorn bridge. The ac-magnetic field superimposed on the earth's field was applied to the specimen. We observed nonzero values of chi(n) for all n in the temperature range of the superconducting transition. The observed chi(n)-T curves were analyzed by the Kim-Anderson critical-state model. We found that the pinning force density increases up to x = 0.5 and decreases over x = 0.5 with increasing the Ca content x, and is proportional to two kinds of the power of the elemental pinning force. (C) 2002 Elsevier Science B.V. All rights reserved.