Local Texture and Magnetic Levitation Force of YBaCuO Cylinders

摘要

YBaCuO cylinders are needed for the construction of magnetic bearings. In these YBaCuO cylinders superconducting currents are induced by approaching a permanent magnet. To obtain a high induced current in concentric circles around the cylinder axis of the YBaCuO cylinder, the c-axes of the crystalline domains have to be aligned as well as possible in normal direction to the induced superconducting currents. This condition is fulfilled, if the c-axes of the domains are in parallel to the cylinder axis of the YBaCuO cylinder. But it allows the c-axes to be tilted each in a same plane with the cylinder axis. Global texture cannot distinguish between different tilting directions of the c-axes of individual parts of the specimen. Therefore, the cylindrical specimen has been cut into 9 pieces, one central piece and 8 boundary pieces. An equal area texture measurement by neutron diffraction has been performed at the Geesthacht reactor with a grid width of 1.5° in the central region of the pole sphere up to △_X = 19.5° from the cylinder axis of the YBaCuO cylinder. For each of the 9 parts of the specimen this neutron texture measurement has been performed. The best suited distribution of the c-axes has been determined in the central piece. The orientation distribution of the c-axes has been found to be broadened at the boundary pieces, especially in diagonal direction of the rectangular seed crystal which was implanted in the molten state into the center of the recrystallized specimen.