Superconducting wires areelectrical wires made ofsuperconductive material. When cooled below theirtransition temperatures, they have zeroelectrical resistance. Most commonly, conventional superconductors such asniobium–titanium are used,^[1] but high-temperature superconductors such asYBCO are entering the market.

Superconducting wire's advantages overcopper or aluminum include higher maximumcurrent densities and zero powerdissipation. Its disadvantages include the cost ofrefrigeration of the wires to superconducting temperatures (often requiringcryogens such asliquid nitrogen orliquid helium), the danger of the wirequenching (a sudden loss of superconductivity), the inferior mechanical properties of some superconductors, and the cost of wire materials and construction.^[2]

Its main application is insuperconducting magnets, which are used in scientific and medical equipment where high magnetic fields are necessary.

The construction andoperating temperature will typically be chosen to maximise:

• Critical temperature T_c, the temperature below which the wire becomes a superconductor
• Criticalcurrent density J_c, the maximumcurrent a superconducting wire can carry per unit cross-sectional area (see images below for examples with 20 kA/cm²).

Superconducting wires/tapes/cables usually consist of two key features:

• The superconducting compound (usually in the form of filaments/coating)
• A conduction stabilizer, which carries the current in case of the loss of superconductivity (known asquenching) in the superconducting material.^[3][4]

The current sharing temperature T_cs is the temperature at which the current transported through the superconductor also starts to flow through the stabilizer.^[5][6] However, T_cs is not the same as the quench temperature (or critical temperature) T_c; in the former case, there is partial loss of superconductivity, while in the latter case, the superconductivity is entirely lost.^[7]

Low-temperature superconductor (LTS) wires are made from superconductors with lowcritical temperature, such as Nb₃Sn (niobium–tin) and NbTi (niobium–titanium). Often the superconductor is in filament form in a copper or aluminium matrix which carries the current should the superconductor quench for any reason. The superconductor filaments can form a third of the total volume of the wire.

The normalwire-drawing process can be used for malleable alloys such as niobium–titanium.

Vanadium–gallium (V₃Ga) can be prepared by surface diffusion where the high temperature component as a solid is bathed in the other element as liquid or gas.^[8] When all components remain in the solid state during high temperature diffusion this is known as the bronze process.^[9]

• 
  Cross sections of various (Nb,Ti)₃Sn composite superconducting cables and wires. (440 to 7,800 A in 8 to 19 tesla fields).
• 
  V₃Ga superconducting tape (10×0.14 mm cross section). A vanadium core is covered with 15 μm V₃Ga layer, then 20 μm bronze (stabilizing layer) and 15 μm insulating layer. Critical current 180 A (19.2 tesla, 4.2 K), critical current density 20 kA/cm²
• 
  Nb/Cu–7.5at%Sn–0.4at%Ti tape (9.5×1.8 mm cross section) originally developed for an 18.1 T magnet. Nb core: 361×348 packs of 5 μm dia. filaments. Critical current 1700 A (16 tesla, 4.2 K), critical current density 20 kA/cm²

High-temperature superconductor (HTS) wires are made from superconductors with highcritical temperature (high-temperature superconductivity), such asYBCO andBSCCO.

The powder-in-tube (PIT, oroxide powder in tube, OPIT) process is anextrusion process often used for making electrical conductors from brittlesuperconducting materials such asniobium–tin^[10] ormagnesium diboride,^[11] and ceramiccuprate superconductors such asBSCCO.^[12][13] It has been used to form wires of theiron pnictides.^[14] (PIT is not used for yttrium barium copper oxide as it does not have the weak layers required to generate adequate 'texture' (alignment) in the PIT process.)

This process is used because thehigh-temperature superconductors are too brittle fornormal wire forming processes. The tubes are metal, oftensilver. Often the tubes are heated to react the mix of powders. Once reacted the tubes are sometimes flattened to form a tape-like conductor. The resulting wire is not as flexible as conventional metal wire, but is sufficient for many applications.

There arein situ andex situ variants of the process, as well a 'double core' method that combines both.^[15]

These wires are in a form of a metal tape of about 10 mm width and about 100 micrometer thickness, coated with superconductor materials such asYBCO. A few years after the discovery ofHigh-temperature superconductivity materials such as theYBCO, it was demonstrated thatepitaxialYBCOthin films grown on lattice matchedsingle crystals such as magnesium oxideMgO,strontium titanate (SrTiO₃) andsapphire had high supercritical current densities of 10–40 kA/mm².^[16][17] However, a lattice-matched flexible material was needed for producing a long tape. YBCO films deposited directly on metal substrate materials exhibit poor superconducting properties. It was demonstrated that a c-axis oriented yttria-stabilized zirconia (YSZ) intermediate layer on a metal substrate can yield YBCO films of higher quality, which had still one to two orders less critical current density than that produced on the single crystal substrates.^[18][19]

The breakthrough came with the invention ofion beam-assisted deposition (IBAD) technique to produce of biaxially alignedyttria-stabilized zirconia (YSZ) thin films on metal tapes and the Rolling-Assisted-Biaxially-Textured-Substrates (RABiTS) process to produce biaxially textured metallic substrates via thermomechanically processing.^[20][21]

In the IBAD process, the biaxially-textured YSZ film provided a single-crystal-like template for theepitaxial growth of the YBCO films. These YBCO films achieved critical current density of more than 1 MA/cm². Other buffer layers such ascerium oxide (CeO₂) andmagnesium oxide (MgO) were produced using theIBAD technique for the superconductor films.^[22][23] Details of the IBAD substrates and technology were reviewed by Arendt.^[24] The process of LMO-enabled IBAD–MgO was invented and developed at the Oak Ridge National Laboratory and won a R&D100 Award in 2007.^[25] This LMO-enabled substrate process is now being used by essentially all manufacturers of HST wire based on the IBAD substrate.In the RABiTS substrates, the metallic template itself was biaxially-textured and heteroepitaxial buffer layers of Y₂O₃, YSZ and CeO₂ were then deposited on the metallic template, followed by heterepitaxial deposition of the superconductor layer. Details of the RABiTS substrates and technology were reviewed by Goyal.^[26]

As of 2015^[update], YBCO coated superconductor tapes capable of carrying more than 500 A/cm-width at 77 K and 1000 A/cm-width at 30 K under high magnetic field have been demonstrated.^{[27][28][29][30]} In 2021 YBCO coated superconductor tapes capable of carrying more than 250 A/cm-width at 77 K and 2500 A/cm-width at 20 K were reported for commercially produced wires.^[31] In 2021 an experimental demonstration of an over-doped YBCO film reported 90 MA/cm² at 5 K and 6 MA/cm² at 77 K in a 7 T magnetic field.^[32]

Metal organic chemical vapor deposition (MOCVD) is one of the deposition processes used for fabrication ofYBCO coated conductor tapes. Ignatiev provides an overview of MOCVD processes used to depositYBCO films via MOCVD deposition.^[33]

Superconducting layer in the 2nd generation superconducting wires can also be grown by thermal evaporation of constituent metals,rare-earth element,barium, andcopper. Prusseit provides an overview of the thermal evaporation process used to deposit high-qualityYBCO films.^[34]

Superconducting layer in the 2nd generation superconducting wires can also be grown by pulsed laser deposition (PLD). Christen provides an overview of the PLD process used to deposit high-qualityYBCO films.^[35]

There are several IEC (International Electrotechnical Commission) standards related to superconducting wires under TC90.

• Copper-clad aluminium wire
• Graphene-clad wire
• Skin effect
• Residual-resistivity ratio

• Superconductors
• Wire

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