INFLUENCE OF MICROSTRUCTURE ON POWER DISSIPATION IN BULK Y-BA-CU-O STRUCTURES

The relatively low values of critical current density (J(c)) in bulk h igh T-c materials are a problem for many applications, but these mater ials are now finding use in developmental fault current limiters of va rious design. Intended primarily for AC power applications, these devi ces rely on materials that transition quickly between a state of effec tively lossless conduction and a state which dissipates significant po wer directly or significantly changes the magnetic coupling between ot her circuit elements, Most bulk material processes have been adjusted to maximize the value of J(c) rather than to provide the well defined, sharp transition just mentioned, This study compares the dissipative properties of sintered YBCO with equiaxed, unoriented grains to that o f two different types of melt-processed thick film material with plate -like grains in c-axis orientation. Dissipative properties are measure d under current densities of 10 times J(c) or more. Isothermal conditi ons are maintained through the use of submillisecond feedback-controll ed current pulses. Significant differences are noted in the high-curre nt flux flow properties, with the sintered samples developing Ohmic be havior and the samples with oriented microstructures developing voltag es proportional to I-2 Sharp transitions at J(c) and extreme dependenc e on applied magnetic field were noted in all cases.