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Why was yttrium barium copper oxide important for superconductivity research?

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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.

Yttrium barium copper oxide (YBCO) was a landmark discovery in superconductivity research because it was the first material found to exhibit a superconducting transition temperature ( $T_{c}$ ) above 77 K, the boiling point of liquid nitrogen.12

Prior to this discovery, superconducting materials required cooling with expensive liquid helium. By enabling the use of inexpensive liquid nitrogen for cooling, YBCO revolutionized the field and opened the door to more practical applications of superconductivity. Furthermore, its discovery was highly significant because it was a ceramic oxide; at the time, researchers primarily expected high-temperature superconductivity to be found in metallic alloys.213

Structurally, YBCO features a layered, perovskite-like arrangement characterized by two-dimensional copper-oxygen sheets. These sheets are the critical pathways along which superconduction occurs. Because the material is severely anisotropic—meaning its properties vary significantly depending on the direction—the alignment of these copper-oxygen sheets is a vital consideration in the fabrication of YBCO ceramics for high-current applications.124