Abstract
Phase evolution in the BiSrCaCuAlO system was studied. Two Al-containing phases BiSr 1.5Ca 0.5Al 2O z and (Sr 1− x Ca x ) 3Al 2O 6 ( x = 0.4 − 0.45) were determined to be chemically compatible with Bi 2.18Sr 2CaCu 2O 8+ x (Bi-2212) at temperatures of the samples processing. The phase equilibria in the title system were investigated above the solidus temperature. The BiSr 1.5Ca 0.5Al 2O z was found to be in equilibrium only with the melt and the (Sr 1− x Ca x ) 3Al 2O 6 phase. This latter aluminate equilibrated with Ca,Sr cuprates, CaO, the Cu-free phase, and the liquid. The melting and solidification in Bi-2212, doped with the aluminate, corresponded to the reversible reaction Bi-2212 + BiSr 1.5Ca 0.5Al 2O z ↔ (Sr 1− x Ca x ) 3Al 2O 6 + liquid. Two sets of superconducting composite materials with initial compositions Bi-2212 + nBiSr 1.5Ca 0.5Al 2O z and Bi-2212 + m(Sr 1− x Ca x ) 3Al 2O 6 were prepared by solidification from the partial melt. The former material was composed mostly of large Bi-2212 lamellas separated by the BiSr 1.5Ca 0.5Al 2O z phase, which destroyed superconducting links between Bi-2212 grains. The latter material consisted of a Bi-2212 polycrystalline matrix with high concentration of small (ca. 3 μm) grains of (Sr 1− x Ca x ) 3Al 2O 6 imbedded in Bi-2212 lamellas. The Bi-2212 + m(Sr 1− x Ca x ) 3Al 2O 6 materials displayed a trend to enhance flux pinning at T = 60 K with the increase of aluminate phase content.
Published Version
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