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What happens to the electrical resistance of a ceramic superconductor below its critical temperature?

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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.

When a ceramic superconductor is cooled below its critical temperature ( $T_{c}$ ), it undergoes a phase transition characterized by the complete disappearance of its electrical resistance.123

At this transition point, the material ceases to impede the flow of electrical current, allowing it to conduct electricity without energy loss. In addition to this loss of resistance, these materials typically exhibit the Meissner effect, which is the expulsion of magnetic fields from the interior of the material as it enters the superconducting state.13

While most ceramics are naturally poor conductors due to their ionic or covalent bonding, certain transition-metal oxide ceramics—specifically those with layered copper-oxygen structures—are capable of achieving this state at relatively high critical temperatures compared to traditional metal alloys.14