In chemistry, oxypnictides are a class of materials composed of

oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as wel ...

, a

pnictogen A pnictogen ( or ; from grc, πνῑ́γω "to choke" and -gen, "generator") is any of the chemical elements in group 15 of the periodic table. Group 15 is also known as the nitrogen group or nitrogen family. Group 15 consists of the el ...

(group-V, especially phosphorus and arsenic) and one or more other elements. Although this group of compounds has been recognized since 1995, interest in these compounds increased dramatically after the publication of the superconducting properties of LaOFeP and LaOFeAs which were discovered in 2006 and 2008. In these experiments the oxide was partly replaced by fluoride. These and related compounds (e.g. the 122 iron arsenides) form a new group of

iron-based superconductor Iron-based superconductors (FeSC) are iron-containing chemical compounds whose superconducting properties were discovered in 2006. In 2008, led by recently discovered iron pnictide compounds (originally known as oxypnictides), they were in the firs ...

s known as iron pnictides or ferropnictides since the oxygen is not essential but the iron seems to be. Oxypnictides have been patented as magnetic

semiconductor A semiconductor is a material which has an electrical resistivity and conductivity, electrical conductivity value falling between that of a electrical conductor, conductor, such as copper, and an insulator (electricity), insulator, such as glas ...

s in early 2006. The different subclasses of oxypnictides are oxynitrides, oxyphosphides,

oxyarsenides Oxyarsenides or arsenide oxides are chemical compounds formally containing the group AsO, with one arsenic and one oxygen atom. The arsenic and oxygen are not bound together as in arsenates or arsenites, instead they make a separate presence bound ...

, oxyantimonides, and

oxybismuthides Oxybismuthides or bismuthide oxides are chemical compounds formally containing the group BiO, with one bismuth and one oxygen atom. The bismuth and oxygen are not bound together as in bismuthates, instead they make a separate presence bound to the ...

Structure

Many of the oxypnictides show a layered structure. For example, LaFePO with layers of La³⁺O²⁻ and Fe²⁺P³⁻. This structure is similar to that of ZrCuSiAs, which is now the parent structure for most of the oxypnictide.

Superconductivity

The first

superconducting Superconductivity is a set of physical properties observed in certain materials where Electrical resistance and conductance, electrical resistance vanishes and magnetic field, magnetic flux fields are expelled from the material. Any material e ...

iron oxypnictide was discovered in 2006, based on phosphorus. A drastic increase in the

critical temperature Critical or Critically may refer to: *Critical, or critical but stable, medical states **Critical, or intensive care medicine *Critical juncture, a discontinuous change studied in the social sciences. *Critical Software, a company specializing in ...

was achieved when phosphorus was substituted by arsenic. This discovery boosted the search for similar compounds, like the search for

cuprate Cuprate loosely refers to a material that can be viewed as containing anionic copper complexes. Examples include tetrachloridocuprate ( uCl4sup>2−), the superconductor YBa2Cu3O7, and the organocuprates (e.g., dimethylcuprate u(CH3)2sup>� ...

-based superconductors after their discovery in 1986. The superconductivity of the oxypnictides seems to depend on the iron-pnictogen layers. Some found in 2008 to be

high-temperature superconductors High-temperature superconductors (abbreviated high-c or HTS) are defined as materials that behave as superconductors at temperatures above , the boiling point of liquid nitrogen. The adjective "high temperature" is only in respect to previo ...

(up to 55 K) of composition ReOTmPn, where Re is a rare earth, Tm is a

transition metal In chemistry, a transition metal (or transition element) is a chemical element in the d-block of the periodic table (groups 3 to 12), though the elements of group 12 (and less often group 3) are sometimes excluded. They are the elements that can ...

and Pn is from group V e.g. As. Tests in magnetic fields up to 45 teslas suggest the

upper critical field For a given temperature, the critical field refers to the maximum magnetic field strength below which a material remains superconducting. Superconductivity is characterized both by perfect conductivity (zero resistance) and by the complete expulsi ...

of LaFeAsO_0.89F_0.11 may be around 64 T. A different

lanthanum Lanthanum is a chemical element with the symbol La and atomic number 57. It is a soft, ductile, silvery-white metal that tarnishes slowly when exposed to air. It is the eponym of the lanthanide series, a group of 15 similar elements between lantha ...

-based material tested at 6 K predicts an

of 122 T in La_0.8K_0.2FeAsO_0.8F_0.2.

Practical use

Because of the brittleness of the oxypnictides, superconducting wires are formed using the

powder-in-tube Superconducting wires are electrical wires made of superconductive material. When cooled below their transition temperatures, they have zero electrical resistance. Most commonly, conventional superconductors such as niobium-titanium are used, ...

process (using iron tubes).

References

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External links

Hosono at JST
Has diagram of LaO & FeAs layers in LaOFeAs Superconductors

Structure

Superconductivity

Practical use

See also

References

External links