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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