Oxypnictide

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In chemistry, oxypnictides are a class of materials composed of oxygen, a pnictogen (group-V, especially phosphorus and arsenic) and one or more other elements. Although this group of compounds has been recognized since 1995,[1] interest in these compounds increased dramatically after the publication of the superconducting properties of LaOFeP and LaOFeAs which were discovered in 2006[2] and 2008.[3][4] 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 superconductors known as iron pnictides or ferropnictides since the oxygen is not essential but the iron seems to be.

Oxypnictides have been patented as magnetic semiconductors in early 2006.[5]

The different subclasses of oxypnictides are oxynitrides, oxyphosphides, oxyarsenides, oxyantimonides, and oxybismuthides.

Structure

Many of the oxypnictides show a layered structure.[6] For example, LaFePO with layers of La3+O2− and Fe2+P3−.[2] This structure is similar to that of ZrCuSiAs, which is now the parent structure for most of the oxypnictide.[7]

Superconductivity

The first

superconducting iron oxypnictide was discovered in 2006, based on phosphorus.[2] A drastic increase in the critical temperature was achieved when phosphorus was substituted by arsenic.[3] This discovery boosted the search for similar compounds, like the search for cuprate
-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 (up to 55 K) of composition ReOTmPn, where Re is a rare earth, Tm is a transition metal and Pn is from group V e.g. As.[8]

oxypnictides
Material Tc (K)
LaO0.89F0.11FeAs 26[9]
LaO0.9F0.2FeAs 28.5[10]
CeFeAsO0.84F0.16 41[9]
SmFeAsO0.9F0.1 43[9]
La0.5Y0.5FeAsO0.6 43.1[11]
NdFeAsO0.89F0.11 52[9]
PrFeAsO0.89F0.11 52[12]
GdFeAsO0.85 53.5[13]
SmFeAsO~0.85 55[14]

Tests in magnetic fields up to 45

upper critical field of 122 T in La0.8K0.2FeAsO0.8F0.2.[10]

Practical use

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

powder-in-tube process (using iron tubes).[17]

See also

References

External links