A model for texture development in BSCCO high-Tc superconductors

Textured BSCCO superconductors are studied and the various mechanisms for alignment of BSCCO grains addressed. To date, surface energy effects leading to texture development of BSCCO superconductors have been considered only with respect to the free surface of melt-processed Bi-2212 thick films. However, these previous efforts have not included the surface interactions between BSCCO crystals and other solid surfaces present in the BSCCO system. In the present work, a model based on an interfacial energy relation is proposed. In order to verify the model a variety of experiments have been performed. The observation of the microstructure in different BSCCO samples corroborates this model. The following discussion offers a plausible explanation for the various observed phenomena during the partial melt process. During the early stages of solidification, when the peritectic liquid is abundant, BSCCO crystals are rather mobile, facilitating their contact and interaction. As a result, if a crystal has its wide planar c-surface in contact with a foreign surface (e.g. silver substrate, secondary phases, free surface or another BSCCO crystal), it can minimize its surface energy and is likely adhere to that surface. This mechanism, applied to a system with planar constraints, such as a 2212-Ag film, will result in a textured sample, depending on the thickness of the superconducting layer Tn a bulk sample however, BSCCO crystals may only minimize their surface energy by adhering to other BSCCO crystals, which will consequently form clusters of locally aligned crystals, i.e. colonies, with no long-range texture. In this fashion, we may also address the role of silver in promoting texture development in BSCCO superconductors.