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Why does the alignment of grains matter in ceramic superconductors?

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conductive ceramics Figure 1: Schematic diagram of a zirconia oxygen sensor used to monitor automobile exhaust gases. The sensor, approximately the size of a spark plug, is fitted into the exhaust manifold of an automobile engine. The thimble-shaped zirconia sensor, sandwiched between thin layers of porous platinum, is exposed on its interior to outside air and on its exterior to exhaust gas passing through slits in the sensor shield. The two platinum surfaces serve as electrodes, conducting a voltage across the zirconia that varies according to the difference in oxygen content between the exhaust gas and the outside air.

In ceramic superconductors, the alignment of grains is critical because of the material's inherent anisotropy, or the variation of physical properties depending on the direction of measurement.1

Most high-temperature ceramic superconductors, such as yttrium barium copper oxide (YBCO), possess a layered crystal structure. Superconduction occurs primarily along two-dimensional copper-oxygen sheets within these layers. Because the transport of electrons perpendicular to these sheets is not favored, the material's ability to conduct electricity is highly directional.21

To fabricate ceramic superconductors capable of carrying large currents, it is essential to align the individual grains so that their copper-oxygen sheets are oriented in the same direction. If the grains are randomly oriented, the internal boundaries between them can impede the flow of current, significantly limiting the material's performance in practical applications like superconducting magnets or power transmission lines.12