Preparation, structure, and properties of the superconducting compound series Bi2Sr2Can-1CunOy with n=1,2, and 3

Crystals of the three Bi-based cuprates of general formula Bi2Sr2Can-1CunOy with n=1,2, and 3 have been isolated and their structural and physical properties investigated. The structures are similar, differing only in the number of CuO2-Ca-CuO2 slabs packed along the c axis. The insertion of one and two slabs increases c from 24.6 to 30.6 and 37.1. Transmission electron microscopy shows there are stacking faults within the crystals in agreement with our x-ray data and its analysis. Resistivity, ac susceptibility, and dc magnetization measurements demonstrate superconductivity in the n=1,2, and 3 phases at 10, 85, and 110 K, respectively. The observed transition temperatures and the stacking fault densities are dependent upon sample processing, in particular, the annealing temperatures and cooling rates. The transition temperature is, within the accuracy of our chemical titration, independent of the average copper valency that was determined to be 2.15 0.03 for each of the three compounds.