RFHigh Temperature Superconductors (HTS): Basics and Properties
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This article explores the fundamentals of High Temperature Superconductors (HTS), including the materials used and their unique properties.
The Need for HTS: Overcoming Limitations of Copper
Traditional copper conductors, while widely used, have limitations. They can only carry a limited current, typically around 1 to 5 amperes per square millimeter (A/mm²). Furthermore, they suffer from significant power losses, especially over long distances.
High Temperature Superconductors: A Game Changer
High Temperature Superconductor (HTS) cables offer a dramatic improvement, capable of carrying current densities greater than 100 A/mm². Even more impressive, they experience minimal power loss, usually less than 2%. This makes them extremely attractive for efficient electric power transmission.
Construction of an HTS Cable
Companies like BASF have developed sophisticated HTS cables using multiple layers. A typical construction includes:
- Optional Protective Layer: Made of silver, gold, or copper, this layer protects the underlying materials.
- HTS Layer: The heart of the cable, typically composed of materials like MgO, YBa₂Cu₃Oₓ, or REBa₂Cu₃Oₓ.
- Buffer Layer: This layer optimizes the interface between the HTS layer and the metal substrate.
- Metal Substrate: Provides structural support for the cable.
Transition Temperature: The Defining Characteristic
The key difference between ordinary superconductors and HTS materials lies in their transition temperature. Ordinary superconductors typically have transition temperatures below 30 Kelvin (approximately -243.2 degrees Celsius). HTS materials, on the other hand, boast transition temperatures around 138 Kelvin or higher. The transition temperature is the point below which a material becomes superconducting.
Initially, compounds of oxygen and copper were prominent in HTS research. However, numerous other compounds exhibiting HTS properties have since been discovered. High Temperature Superconducting materials also demonstrate a gradual change in transition temperature as the magnetic field changes.
The first high-temperature superconductor was discovered by researchers at IBM.
Oxide Superconductors: A Variety of Structures and Temperatures
The following table lists several oxide superconductors, along with their crystal structures and transition temperatures (Tc).
| Compound | Tc (Kelvin) | Crystal Structure |
|---|---|---|
| Y-Based YBa₂Cu₃O₇ | 92 | Orthorhombic |
| Bi Based Bi₂Sr₂CuO₆ | 20 | Tetragonal |
| Bi Based Bi₂Sr₂CaCu₂O₈ | 85 | Tetragonal |
| Bi Based Bi₂Sr₂Ca₂Cu₃O₆ | 110 | Tetragonal |
| TI-Based TI₂Ba₂CuO₆ | 84 | Tetragonal |
| TI-Based TI₂Ba₂CaCu₂O₈ | 108 | Tetragonal |
| TI-Based TI₂Ba₂Ca₂Cu₃O�?₀ | 125 | Tetragonal |
| TI-Based TIBa₂Ca₃Cu₄O�?�? | 122 | Tetragonal |
| Hg-Based HgBa₂CuO₄ | 94 | Tetragonal |
| Hg-Based HgBa₂CaCu₂O₆ | 128 | Tetragonal |
| Hg-Based HgBa₂Ca₂Cu₃O₈ | 134 | Tetragonal |
As you can see, Y-based, Bi-based, TI-based, and Hg-based compounds are common ingredients in high-temperature superconductors.
Applications of High Temperature Superconductors
HTS materials have a wide range of potential applications:
- Power Transmission: HTS cables offer a solution for efficient power transmission, particularly in densely populated urban areas.
- Renewable Energy Sources: HTS technology simplifies the integration of renewable energy sources like wind and hydropower into the grid. It makes it possible to harvest energy efficiently using wind and hydro power generators.
- Magnetic Trains: The Meissner effect, which is the expulsion of magnetic fields in the superconducting state, is leveraged in magnetically levitated (Maglev) trains. These trains experience no friction between wheels and tracks, enabling very high speeds. The powerful magnetic field generated by superconductors is used both to levitate and propel the trains.
- Magnetic Resonance Imaging (MRI): The strong magnetic fields produced by superconductors are used in MRI machines for scanning and imaging the human body.
