Rare-earth barium copper oxide

Rare-earth barium copper oxides are layered ceramic superconductors with composition REBa₂Cu₃O₇−δ, where RE is a rare-earth element and oxygen deficiency tunes their properties. Their superconductivity can persist above the boiling point of liquid nitrogen.

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Cuprate superconductivity: Superconductivity in layered copper-oxide compounds, marked by high transition temperatures and strong electronic anisotropy. REBa₂Cu₃O₇−δ is one prominent family within the broader cuprate class.
Perovskite structure: A crystal structure built around a framework of corner-sharing octahedra, with several common distorted forms. The layered structure of these compounds derives from perovskite-like building blocks.
High-temperature superconductivity: Superconductivity occurring at temperatures high relative to conventional superconductors, including materials usable with liquid nitrogen cooling. This family helped establish cuprates as technologically accessible high-temperature superconductors.
Superconductivity: A state in which a material has zero direct-current electrical resistance and expels magnetic fields below a critical temperature. The family became a landmark example of superconductivity at unusually high temperatures.
Conventional superconductor: A superconductor generally described by phonon-mediated pairing and conventional Bardeen–Cooper–Schrieffer theory. REBCO reaches higher transition temperatures, while its pairing mechanism is not settled in the same way.
Oxygen stoichiometry: The quantitative ratio of oxygen atoms to other elements in a material. Changing δ alters carrier concentration and can suppress or enable superconductivity.
Yttrium barium copper oxide: The YBa₂Cu₃O₇−δ member of the rare-earth barium copper oxide family, often called YBCO. YBCO is the best-known composition and a common reference for the family.
Liquid nitrogen: Nitrogen cooled below its boiling point of about 77 kelvins at atmospheric pressure. Many compositions operate below this temperature, making cooling comparatively inexpensive.
Bednorz and Müller: J. Georg Bednorz and K. Alex Müller, physicists who discovered superconductivity in a copper-oxide ceramic in 1986. Their discovery of superconductivity in a lanthanum barium copper oxide prompted the cuprate search.
Magnesium diboride: A metallic compound that becomes superconducting below about 39 kelvins. It is a simpler, conventional superconductor with a substantially lower transition temperature.