Homogeneity area of Bi₂Sr₂CaCu₂O₈ - based solid solutions with substitution of alkaline earth elements by Nd and La

Abstract

Creation of precipitates in bulk matrix to act as pinning centres is a prospective way to improve critical current density in high temperature superconductors. It is possible to generate such precipitates via partial decomposition of the supersaturated solid solution derived from a superconducting phase. To control this process one should go by a knowledge of stability field for these solutions. The objective of present work was determination of the homogeneity area of Bi₂Sr₂Ca_1−xR_xCu₂O_8+d and Bi₂Sr_2−xCaR_xCu₂O_8+d (R = Nd, La). Semi-quantitative XRD analysis was used to evaluate phase composition of specimens quenched from various temperatures. It was found that solubility limits of Nd and La in Bi-2212 for cases of alkaline earth element substitution by rare earth elements with smaller ionic radii (substitution Ca by Nd; Sr by Nd and La) were the same (values of x are about 0.8). These limits are determined by fraction of Cu⁺ ions in lattice site attributed to Cu²⁺. In case of substitution of Ca by La stability area of 2212 was found to be much narrower (values of x about 0.3) compared to other substitutions. One ca n deduce this fact from the difference of Ca²⁺ and La³⁺ ionic radii.