Fluctuation-induced excess conductivity in the compounds CaREBaCu3O7−y (RE=La and Sm)

Abstract

The compounds CaREBaCu3O7−y (RE=La and Sm) are tetragonal at room temperature withT c between 60 and 70 K. The single-phase compounds were prepared by solid-state reaction. The resistivity was measured by a four-probe technique in a continuous flow cryostat with the temperature being controlled to an accuracy of 10 mK. The resistivity vs temperature showed a break in slope around 180 K in CaLaBaCu3O7−y and around 220 K in CaSmBaCu3O7−y . The results were analysed for fluctuation conductivity from 180 K downwards. A plot of dρ/dT vsT showed a sharp peak atT m =69·69 K for La compound and 66·00 K for the Sm compound. Detailed analysis of the resistivity in the regionT on to 180 K was carried out using the procedure due to Veira and Vidal. The results are discussed in this paper.