Breakthrough Iron-based Superconductors Set New Performance Records

Brookhaven National Laboratory has created a high performance iron-based superconducting wire that opens new pathways for some of the most essential and energy-intensive technologies in the world. These custom-grown materials carry tremendous current under exceptionally high magnetic fields—an order of magnitude higher than those found in wind turbines, magnetic resonance imaging (MRI) machines, and even particle accelerators. The results demonstrate a unique layered structure that outperforms competing low-temperature superconducting wires while avoiding the high manufacturing costs associated with high-temperature superconductor (HTS) alternatives.

Nature Communications – High current superconductivity in FeSe0.5Te0.5-coated conductors at 30 tesla

Iron-based superconductors are mechanically semi-metallic and therefore considerably less fragile than ceramic superconductors. They can also be more easily shaped into the kinds of long wires needed in devices like massive offshore wind turbines, and they exhibit nearly isotropic behavior in magnetic fields, which allows for easier technology integration.

The scientists synthesized this novel film of iron, selenium, and tellurium to push existing performance parameters. In addition to the raw materials being relatively inexpensive, the synthesis process itself can be performed at just half the temperature of cuprate-based HTS alternatives, or approximately 400 degrees Celsius.

The team used a thin film fabrication technique called pulsed-laser deposition, which uses a high-power laser to vaporize materials that are then collected in layers on a substrate. This complex technique is a bit like carefully collecting the gas as it rises above a boiling pot, only with nearly atomic-level precision.

“A key breakthrough here is the discovery that adding layers of cesium-oxide in between the films and substrates dramatically increased the superconductor’s critical current density, or maximum electricity load, as well as the critical temperature at which the material becomes superconducting,” said Brookhaven Lab physicist Qiang Li, head of the Advanced Energy Materials Group and leader of this study. “That critical temperature threshold rose 30 percent over the same compound made without this layering process—still a very cold -253 degrees Celsius, but it promises significant application potential.”

When tested, the critical current density of the new iron-based superconductor reached more than 1 million amperes (amps) per square centimeter, which is several hundred times more than regular copper wires can carry over the same area. Under an intense 30-tesla magnetic field, the film carried a record-high 200,000 amperes per square centimeter. For scale, consider that household circuit breakers usually blow when hitting just 20 amps.

In devices such as MRIs, using electricity to generate powerful magnetic fields is essential, and the magnetic tolerance of the superconducting wires must be high. The thin films in the new study remained functional under that 30-tesla magnetic field, while most hospital MRIs require just 1-3 tesla.

The researchers extended the study to include thin films grown on flexible metallic materials called rolling-assisted biaxial textured substrates, or RABiTS. These substrates, developed in a proprietary process invented by scientists at DOE’s Oak Ridge National Laboratory, offered a similar performance with particularly important implications for long-length scaled up production in the future.

“We believe both critical current and transition temperatures can be further improved as we fine-tune the structure and chemical composition,” Qiang Li said. “The next step is to pinpoint the mechanism behind the findings—the relationship between the structure and properties—which will provide guidance for the discovery of new superconductors with even greater performance.”

ABSTRACT – Although high-temperature superconductor cuprates have been discovered for more than 25 years, superconductors for high-field application are still based on low-temperature superconductors, such as Nb3Sn. The high anisotropies, brittle textures and high manufacturing costs limit the applicability of the cuprates. Here we demonstrate that the iron superconductors, without most of the drawbacks of the cuprates, have a superior high-field performance over low-temperature superconductors at 4.2 K. With a CeO2 buffer, critical current densities over 10^6  A cm−2 were observed in iron-chalcogenide FeSe0.5Te0.5 films grown on single-crystalline and coated conductor substrates. These films are capable of carrying critical current densities exceeding 10^5 A cm−2 under 30 tesla magnetic fields, which are much higher than those of low-temperature superconductors. High critical current densities, low magnetic field anisotropies and relatively strong grain coupling make iron-chalcogenide-coated conductors particularly attractive for high-field applications at liquid helium temperatures.

SOURCES- Brookhaven National Lab, Nature Communications

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