Cuprate
Cuprate loosely refers to a material that can be viewed as containing anionic copper complexes. Examples include tetrachloridocuprate ([CuCl4]2−), the superconductor YBa2Cu3O7, and the organocuprates ([Cu(CH3)2]−). The term cuprates derives from the Latin word for copper, cuprum. The term is mainly used in three contexts - oxide materials, anionic coordination complexes, and anionic organocopper compounds.
One of the simplest oxide-based cuprates is the copper(III) oxide KCuO2. This species can be viewed as the K+ salt of the polyanion [CuO2−]n. As such the material is classified as a cuprate. This dark blue diamagnetic solid is produced by heating potassium peroxide and copper(II) oxide in an atmosphere of oxygen:
Interest in cuprates sharply increased in 1986 with the discovery of high-temperature superconductivity in the Non-stoichiometric cuprate lanthanum barium copper oxide La2-xBaxCuO4. The Tc for this material was 35 K, well above the previous record of 23K. Thousands of publications examine the superconductivity in cuprates between 1986 and 2001, and Bednorz and Müller were awarded the Nobel Prize in Physics only a year after their discovery.
From 1986 to 2008, many cuprate superconductors were identified. Most famous is yttrium barium copper oxide (YBa2Cu3O7, "YBCO" or "1-2-3"). Another example is bismuth strontium calcium copper oxide (BSCCO or Bi2Sr2CanCun+1O2n+6-d) with Tc = 95–107 K depending on the n value. Thallium barium calcium copper oxide (TBCCO, TlmBa2Can−1CunO2n+m+2+δ) was the next class of high-Tc cuprate superconductors with Tc = 127 K observed in Tl2Ba2Ca2Cu3O10 (TBCCO-2223) in 1988. The highest confirmed, ambient-pressure, Tc is 135 K, achieved in 1993 with the layered cuprate HgBa2Ca2Cu3O8+x. Few months later, another team measured superconductivity above 150K in the same compound under applied pressure (153 K at 150 kbar).
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