Influence of strontium vacancies on the superconductivity of Bi2Sr2−z−xLaxCuO6+y

Abstract

Ceramic samples in the series Bi2Sr2-z-x LaxCuO6 + y (0.1 ≤ x ≤ 1) have been prepared and investigated by chemical analysis, X-ray diffraction and low-field AC magnetic susceptibility. Elemental analysis shows that the maximum (Sr + La) incorporated per formula unit is 1.9. Comparison of two series with a different concentration of Sr vacancies shows that To is highly dependent on the Sr content, decreasing as z increases. The maximum To value corresponds to a hole concentration in the planes of 0.15, in agreement with other HTSC families. A full correlation is found among To and the diamagnetic shielding ratio of the powders, for the two investigated series. The origin of the reduced shielding capability of these superconductors, when moving far from the optimal hole concentration, is discussed.