Detailed Study of the
Process of Biomimetic Formation
of YBCO Platelets from Nitrate Salts in the Presence of the Biopolymer
Dextran and a Molten NaCl Flux
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Abstract
A novel method of achieving microscopic morphological
control during
the bulk synthesis of the high temperature superconducting ceramic
YBa<sub>2</sub>Cu<sub>3</sub>O<sub>7</sub> (YBCO) has been studied.
By incorporating appropriate amounts of the additives dextran (a biopolymer)
and NaCl (a high melting point ionic salt) into the synthesis protocol,
it is proven possible to engineer high aspect ratio (platelet) growth
of the YBCO crystallites together with localized orientational ordering
between adjacent densely packed crystallites. In the optimized protocol,
both additives are fully consumed during the synthesis by decomposition
(dextran) and vaporization (NaCl), leaving phase-pure YBCO as the
final synthesis product. The individual effects of the two additives
are separately described and their optimal quantities determined.
Routes toward improving the yield and increasing the aspect ratio
of the resulting
crystallites are outlined. The method is likely applicable to the
synthesis of other ceramic materials as an alternative to the conventional
solid state synthesis route, where a higher degree of connectivity
between crystallites is required than can be achieved through sintering