A model for texture development in BSCCO high-Tcsuperconductors

Abstract

Textured BSCCO superconductors are studied and the variousmechanisms for alignment of BSCCO grains addressed. To date, surface energyeffects leading to texture development of BSCCO superconductors have beenconsidered only with respect to the free surface of melt-processed Bi-2212thick films. However, these previous efforts have not included the surfaceinteractions between BSCCO crystals and other solid surfaces present in theBSCCO system. In the present work, a model based on an interfacial energyrelation is proposed. In order to verify the model a variety of experimentshave been performed. The observation of the microstructure in different BSCCOsamples corroborates this model. The following discussion offers a plausibleexplanation for the various observed phenomena during the partial meltprocess. During the early stages of solidification, when the peritectic liquidis abundant, BSCCO crystals are rather mobile, facilitating their contact andinteraction. As a result, if a crystal has its wide planar c-surface incontact with a foreign surface (e.g. silver substrate, secondary phases, freesurface or another BSCCO crystal), it can minimize its surface energy and islikely adhere to that surface. This mechanism, applied to a system with planarconstraints, such as a 2212-Ag film, will result in a textured sample,depending on the thickness of the superconducting layer. In a bulk samplehowever, BSCCO crystals may only minimize their surface energy by adhering toother BSCCO crystals, which will consequently form clusters of locally alignedcrystals, i.e. colonies, with no long-range texture. In this fashion, we mayalso address the role of silver in promoting texture development in BSCCOsuperconductors.