Bi2Sr2CaCu2O8

Bi2Sr2CaCu2O8, commonly referred to as Bi-2212, is a bismuth-based high-temperature superconductor in the Bi-Sr-Ca-Cu-O family. Its superconducting transition temperature is typically around 85–95 K for optimally oxygen-doped samples, placing it among the well-studied cuprate superconductors.

Crystal and composition: Bi-2212 fits the general Bi2Sr2Can−1CunO2n+4+δ formula with n = 2. The structure is highly layered, consisting of CuO2 planes that carry the superconducting current, separated by strata of Sr-O and Ca layers, and flanked by Bi-O charge reservoir layers. This bilayer cuprate contains two CuO2 planes per formula unit. The Bi-O layers exhibit a characteristic incommensurate modulation along one crystallographic direction, a feature common to Bi-based cuprates.

Synthesis and doping: Bi-2212 can be synthesized by solid-state reaction and grown as single crystals using techniques such as the floating-zone method or flux growth. Oxygen content strongly influences carrier concentration and Tc, with annealing in oxygen typically enhancing superconducting properties and achieving higher Tc values in optimally doped samples.

Physical properties: The material is highly anisotropic, with superconductivity concentrated in the CuO2 planes and markedly weaker coupling along the c-axis. It behaves as a type-II superconductor with vortex states in a magnetic field. Bi-2212 is relatively thermally and chemically stable for a cuprate but remains sensitive to oxygen content and microstructure, which affect critical current and other properties.

Applications and significance: Bi-2212 is extensively used in fundamental studies of high-temperature superconductivity, as well as in thin-film devices and superconducting electronics, including junctions and microfabricated structures. It serves as a key model system for bilayer cuprates and layered superconductivity.