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.
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]
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]
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 teslas [15] [16] suggest the upper critical field of LaFeAsO0.89F0.11 may be around 64 T. A different lanthanum-based material tested at 6 K predicts an upper critical field of 122 T in La0.8K0.2FeAsO0.8F0.2. [10]
Because of the brittleness of the oxypnictides, superconducting wires are formed using the powder-in-tube process (using iron tubes). [17]
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.
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]
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]
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 teslas [15] [16] suggest the upper critical field of LaFeAsO0.89F0.11 may be around 64 T. A different lanthanum-based material tested at 6 K predicts an upper critical field of 122 T in La0.8K0.2FeAsO0.8F0.2. [10]
Because of the brittleness of the oxypnictides, superconducting wires are formed using the powder-in-tube process (using iron tubes). [17]