Homogeneity area of Bi2Sr2Ca(1-x)R(x)Cu2O(8+d) (R = Nd, La) solid solutions.

A.V. Knotko, D.V. Korolyov, A.V. Garshev, V.I. Putlayev

Abstracts of MRS'99 Fall Meeting, 29.11 - 3.12.99, Boston, USA, II3.15, p. 603

ABSTRACT. Creation of precipitates in bulk matrix to act as pinning centers is a perspective way to improve critical current density in high temperature superconductors. It is possible to generate such precipitates via partial decomposition of 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 consisted in determination of homogeneity area of Bi2Sr2Ca(1-x)R(x)Cu2O(8+d) (R = Nd, La). Semi-quantitative XRD analysis was used to determine phase composition of specimens quenched from various temperatures. Annealing time appropriate to attain equilibrium in powder mixture was evaluated through kinetics measurements. It was found that lower temperature limit of stability field of Bi-2212 based solid solutions in multiphase mixture is 750 C. Monophase solid solutions exist in relatively narrow temperature interval. This interval is significantly larger in the case of Nd-doped Bi-2212. It stretches to x=0.45 while temperature is within 825 - 880 C. Solubility limit of Nd corresponds to x=0.75 at 850 C. In the case of Bi2Sr2Ca(1-x)La(x)Cu2O(8+d) solid solutions the maximum substitution was achieved at x = 0.3 and 875 C.
Features of homogeneity fields for both solutions are discussed in terms of ionic radii of the dopants.

Laboratory of Inorganic Materials Science