High-temperature superconductor (HTS) wires are made from superconductors with high
critical temperature (
high-temperature superconductivity), such as
YBCO and
BSCCO.
Powder-in-tube The powder-in-tube (PIT, or
oxide powder in tube, OPIT) process is an
extrusion process often used for making electrical conductors from brittle
superconducting materials such as
niobium–tin or
magnesium diboride, and ceramic
cuprate superconductors such as
BSCCO. It has been used to form wires of the
iron pnictides. (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 the
high-temperature superconductors are too brittle for
normal wire forming processes. The tubes are metal, often
silver. 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 are
in situ and
ex situ variants of the process, as well a 'double core' method that combines both.
Coated superconductor tape or wire 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 as
YBCO. A few years after the discovery of
High-temperature superconductivity materials such as the
YBCO, it was demonstrated that
epitaxial YBCO thin films grown on lattice matched
single crystals such as magnesium oxide
MgO,
strontium titanate (SrTiO3) and
sapphire had high supercritical current densities of 10–40 kA/mm2. 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. In the IBAD process, the biaxially-textured YSZ film provided a single-crystal-like template for the
epitaxial growth of the YBCO films. These YBCO films achieved critical current density of more than 1 MA/cm2. Other buffer layers such as
cerium oxide (CeO2) and
magnesium oxide (MgO) were produced using the
IBAD technique for the superconductor films. Details of the IBAD substrates and technology were reviewed by Arendt. 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. 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. , 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. 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. 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. ===
Metal organic chemical vapor deposition === Metal organic chemical vapor deposition (MOCVD) is one of the deposition processes used for fabrication of
YBCO coated conductor tapes. Ignatiev provides an overview of MOCVD processes used to deposit
YBCO films via MOCVD deposition.
Reactive co-evaporation Superconducting layer in the 2nd generation superconducting wires can also be grown by thermal evaporation of constituent metals,
rare-earth element,
barium, and
copper. Prusseit provides an overview of the thermal evaporation process used to deposit high-quality
YBCO films.
Pulsed laser deposition 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-quality
YBCO films. == Standards ==