EFFECT OF LA SUBSTITUTION ON T-C AND ELECTRONIC-STRUCTURE OF BI-2201 PHASE

The critical temperature T-c of Bi-2(Sr1-xLax)(2)CuOy increased with i ncreasing x, reached a maximum of 30 K at x = 0.19 and decreased. Dete rmination of the excess oxygen content Delta y by chemical analysis re vealed that Delta y decreased with increasing x. The oxygen content an d conductivity sigma of Bi-1.96(Sr0.81La0.19)(2)Cu1.02Oy were measured as a function of T and P(O-2) at high temperatures and sigma at const ant y was determined as a function of T. It was found that sigma incre ases with the increase in excess oxygen Delta y. Assuming that one exc ess oxygen atom creates two holes, the carrier density n and the mobil ity were calculated. The extension of high-temperature conductivity li nked smoothly with the low-temperature one with the same oxygen conten t when y is high. From the results, an electronic-structure model wher eby the conduction behavior can be interpreted was proposed.