Oxypnictide
Encyclopedia
In chemistry, oxypnictides are a class of materials including 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,
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 arsenide
s) form a new group of iron-based superconductor
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
s in early 2006.
-based superconductors after their discovery in 1986.
The superconductvity 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.
Tests in magnetic fields up to 45 teslas
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.
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
, a pnictogen (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 arsenide
122 iron arsenide
The 122 iron arsenide unconventional superconductors are part of a new class of iron-based superconductors. They form in the tetragonal I4/mmm, ThCr2Si2 type, crystal structure. The shorthand name “122” comes from their stoichiometry; the 122s have the chemical formula XFe2As2, where X = Ca, Ba, Sr...
s) form a new group of iron-based superconductor
Iron-based superconductor
Iron-based superconductors are chemical compounds with superconducting properties. In 2008, led by recently discovered iron pnictide compounds , they were in the first stages of experimentation and implementation...
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
Semiconductor
A semiconductor is a material with electrical conductivity due to electron flow intermediate in magnitude between that of a conductor and an insulator. This means a conductivity roughly in the range of 103 to 10−8 siemens per centimeter...
s in early 2006.
Structure
Many of the oxypnictides show a layered structure. For example LnFePO 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 iron oxypnictide was discovered in 2006, based on phosphorus. A drastic increase in the critical temperature was achieved when phosphorus was substituted by arsenic. This discovery boosted the search for similar compounds, like the search for cuprateCuprate
Cuprates are chemical compounds containing copper anion. Cuprates have been known for centuries and are widely used in inorganic and organic chemistry...
-based superconductors after their discovery in 1986.
The superconductvity 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
Rare earth element
As defined by IUPAC, rare earth elements or rare earth metals are a set of seventeen chemical elements in the periodic table, specifically the fifteen lanthanides plus scandium and yttrium...
, Tm is a transition metal
Transition metal
The term transition metal has two possible meanings:*The IUPAC definition states that a transition metal is "an element whose atom has an incomplete d sub-shell, or which can give rise to cations with an incomplete d sub-shell." Group 12 elements are not transition metals in this definition.*Some...
and Pn is from group-V e.g. As.
| Material | Tc (K) |
|---|---|
| LaO0.89F0.11FeAs | 26 |
| LaO0.9F0.2FeAs | 28.5 |
| CeFeAsO0.84F0.16 | 41 |
| SmFeAsO0.9F0.1 | 43 |
| La0.5Y0.5FeAsO0.6 | 43.1 |
| NdFeAsO0.89F0.11 | 52 |
| PrFeAsO0.89F0.11 | 52 |
| GdFeAsO0.85 | 53.5 |
| SmFeAsO~0.85 | 55 |
Tests in magnetic fields up to 45 teslas
Tesla (unit)
The tesla is the SI derived unit of magnetic field B . One tesla is equal to one weber per square meter, and it was defined in 1960 in honour of the inventor, physicist, and electrical engineer Nikola Tesla...
suggest the upper critical field
Upper critical field
-Upper critical field:The upper critical field is the magnetic field which completely suppresses superconductivity in a Type II superconductor at 0K ....
of LaFeAsO0.89F0.11 may be around 64 T. A different lanthanum
Lanthanum
Lanthanum is a chemical element with the symbol La and atomic number 57.Lanthanum is a silvery white metallic element that belongs to group 3 of the periodic table and is the first element of the lanthanide series. It is found in some rare-earth minerals, usually in combination with cerium and...
-based material tested at 6 K predicts an upper critical field
Upper critical field
-Upper critical field:The upper critical field is the magnetic field which completely suppresses superconductivity in a Type II superconductor at 0K ....
of 122 T in La0.8K0.2FeAsO0.8F0.2.
Practical use
Because of the brittleness of the oxypnictides, superconducting wires are formed using the powder-in-tube process (using iron tubes).See also
- Andreev reflectionAndreev reflectionAndreev reflection , named after the Russian physicist Alexander F. Andreev, is a type of particle scattering whichoccurs at interfaces between a superconductor and a normal state material . It is a charge-transfer process by which normal current in N is converted to supercurrent in S...
- Charge transfer complexCharge transfer complexA charge-transfer complex or electron-donor-acceptor complex is an association of two or more molecules, or of different parts of one very large molecule, in which a fraction of electronic charge is transferred between the molecular entities. The resulting electrostatic attraction provides a...
- Color superconductivityColor superconductivityColor superconductivity is a phenomenon predicted to occur in quark matter if the baryon density is sufficiently high and the temperature is not too high...
in quarks - Composite Reaction TexturingComposite Reaction TexturingCRT – Composite Reaction Texturing is a process invented at the University of Cambridge by Prof. J.E.Evetts and dr B.A. Glowacki by which ceramic Bi2Sr2CaCu2O8+x superconductor with induced microstructural texture can be used for high current applications such as current leads or resistive fault...
- Conventional superconductorConventional superconductorConventional superconductors are materials that display superconductivity as described by BCS theory or its extensions.Critical temperatures of some simple metals:ElementTc Al1.20Hg4.15Mo0.92Nb9.26Pb7.19...
- covalent superconductorsCovalent superconductorsCovalent semiconductors are such solids as diamond, silicon, germanium, silicon carbide and silicon-germanium where atoms are linked by covalent bonds. Most of those materials, at least in their bulk form, are well studied and rarely hit the front pages of the top scientific journals in the last...
- Iron-based superconductorIron-based superconductorIron-based superconductors are chemical compounds with superconducting properties. In 2008, led by recently discovered iron pnictide compounds , they were in the first stages of experimentation and implementation...
- High-temperature superconductivityHigh-temperature superconductivityHigh-temperature superconductors are materials that have a superconducting transition temperature above . From 1960 to 1980, 30 K was thought to be the highest theoretically possible Tc...
- Homes's law
- Kondo effectKondo effectIn physics, the Kondo effect describes the scattering of conduction electrons in a metal due to magnetic impurities. It is a measure of how electrical resistivity changes with temperature....
- Little-Parks effectLittle-Parks effectThe Little–Parks effect [1] was discovered in 1962 in experiments with empty and thin-walled superconducting cylinders subjected to a parallel magnetic field....
- Magnetic sailMagnetic sailA magnetic sail or magsail is a proposed method of spacecraft propulsion which would use a static magnetic field to deflect charged particles radiated by the Sun as a plasma wind, and thus impart momentum to accelerate the spacecraft...
- National Superconducting Cyclotron LaboratoryNational Superconducting Cyclotron LaboratoryNational Superconducting Cyclotron Laboratory is located on the campus of Michigan State University and is the leading rare isotope research facility in the United States...
- Proximity effect
- Room temperature superconductorRoom temperature superconductorA room-temperature superconductor is a material yet to be discovered which would be capable of exhibiting superconducting properties at operating temperatures above 0° C . This is not strictly speaking "room temperature" A room-temperature superconductor is a material yet to be discovered...
- Rutherford cableRutherford cableA Rutherford cable is a type of superconducting cable used to generate magnetic fields in particle accelerators. The cables are so-called because of the Rutherford Laboratory where the cable design was developed.-External links:...
- Spallation Neutron SourceSpallation Neutron SourceThe Spallation Neutron Source is an accelerator-based neutron source facility that provides the most intense pulsed neutron beams in the world for scientific research and industrial development...
- Superconducting RF
- Superconductor classificationSuperconductor classificationSuperconductors can be classified in accordance with several criteria that depend on our interest in their physical properties, on the understanding we have about them, on how expensive is cooling them or on the material they are made of....
- Superfluid filmSuperfluid filmSuperfluidity and superconductivity are macroscopic manifestations of quantum mechanics. There is considerable interest, both theoretical and practical, in these quantum phase transitions. There has been a tremendous amount of work done in the field of phase transitions and critical phenomenon in...
- Technological applications of superconductivityTechnological applications of superconductivitySome of the technological applications of superconductivity include:* the production of sensitive magnetometers based on SQUIDs* fast digital circuits ,...
- Timeline of low-temperature technologyTimeline of low-temperature technologyThe following is a timeline of low-temperature technology and cryogenic technology .-16th century BCE – 17th century CE :...
- Type-I superconductor
- Type-II superconductorType-II superconductorA Type-II superconductor is a superconductor characterized by the formation of vortex lattices in magnetic field. It has a continuous second order phase transition from the superconducting to the normal state within an increasing magnetic field....
- Unconventional superconductorUnconventional superconductorUnconventional superconductors are materials that display superconductivity which does not conform to either the conventional BCS theory or the Nikolay Bogolyubov's theory or its extensions....
Further reading
External links
- Hosono at JST Has diagram of LaO & FeAs layers in LaOFeAs