Superconductivity came about in 1933. A definition of

Superconductivity was discovered by H,
Kamerlingh Onnes in Leiden in 1911 when he discovered that all electrical
resistivity of mercury miraculously disappeared at a temperature of 4K. For a
long while it was thought that superconducting compounds kept the same
properties as normal metals, i.e. are magnetic, when the Meissner effect came
about in 1933.  A definition of the
Meissner effect is that when a material transitions between the normal and superconducting
phases it expels all magnetic fields. (1) Despite this, full understanding of
the spectacle was not known by scientists until around the 1950’s.  The definition of superconductivity is the
phenomenon of exactly zero electrical resistance and expulsion of magnetic flux
fields when cooled to its critical temperature TC. This is different to perfect conductivity where
magnetic flux does not tend to be expelled. (2) Superconductors have the
potential to be very advantageous, however their remarkably low critical
temperatures often limit their ability to be used. Raising the critical
temperature or finding new superconductors with higher critical temperatures
would be particularly beneficial.
Intercalation is the reversible process of inserting a molecule, atom or ion
between the layers in a crystal lattice. This is often done to change the
properties of a molecule or increase/improve the favourable properties it
already possess’, in this case in combination with increased pressure it allows
superconductivity of FeSe at a much higher critical temperature. (3)
Structure of FeSe:
Iron based superconductors were only recently discovered in 2008 and are
similar to the better known cuprate superconductors in their
quasi-two-dimensional crystal structure. However unlike cuprates, the layers in
FeSe are thought to be the reason the compound has the ability to be a
superconductor as seen in Fig.1. FeSe alone has the TC ? 8K and it
was one of the earlier Iron based superconductors discovered as a PbO structure
type tetrahedral compound. Research has shown that an excess of Fe in the
compound is beneficial to maintaining the stabilisation of the crystal
structure, but the correct stoichiometry is vital to maintaining
superconductivity. (4)
 Fe in interstitial places?? (4)
Common elements/metals
FeSe is intercalated with??

Preparation Techniques:

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One type of superconducting FeSe is
Barium intercalated FeSe. In order to prepare this ?-FeSe needs to ne
synthesised first. One way of doing this is to add Fe and Se, in powder form,
to a mini mill Pulverisette in order to combine them. The pulverisette uses a
centrifugal force as well as a grinding wall to compound the two elements. The
powder product from this can then be pressed into a pallet and vacuum-packed into
a quartz tube which is annealed at   ?1000
°C for around 48 h. Following this the compound is quenched to 410 °C and
tempered for a further 100 h. Ice water is used to quench the compound to form ?-FeSe
and a very small amount of ?-FeSe as a side product. A Schlenk-line can be used
to intercalate other elements, in this case Barium, into the FeSe compound. The
reaction can take place in an ammonia filled line and an Ar occupied glove-box.
Dry ice would then be used to condense NH3 (l) and evacuation and
purification techniques are then used to prepare the apparatus. Two reactions
can take place in order to produce the desired material, one at low temperature
and one at room temperature.
The low temperature reaction can occur in a round bottom flask where a stoichiometric
amount of Ba is added to an amount of ?-FeSe in a solvent. Reaction completion and
solvent removal can take up to 12 h then the product can be dried in a vacuum,
after which X-ray diffraction analysis can be used to determine the correct product
was synthesised.
At Room temperature ?-FeSe powder and a stoichiometric amount of Ba can be
placed in a glass container together with a glass stirrer, the schlenk-line was
evacuated and NH3 (l) would be condensed in the same manner as
above. The reaction mixture would be left stirring at RT for up to 4 days. The
final product can again be analysed by X-Ray Diffraction, in this case and for
Low temperature synthesis the approximate unit cell parameter of the
tetrahedral Ba intercalated FeSe is    ? 8.5 Å. (7)

Another
type of superconducting FeSe that has been recently ascertained is alkali metal
– organic solvent intercalated FeSe that has a Tc ? 45 K. ?-FeSe
itself can be synthesised from high grade powder forms of Fe and Se, in the way
described above for the synthesis of Ba intercalated FeSe. The general formula
of the desired intercalated compound is Ax(C5H5N)yFe2-zSe2
where A = Li, Na, K or Rb.
For the intercalation synthesis a pre-ascertained amount of FeSe would be
combined with an amount of alkali metal dissolved in anhydrous pyridine   ? 0.2 mol dm-3. The reaction
happens at 40 °C and completion can be distinguished upon discolouration of the
solution

Superconductivity was discovered by H,
Kamerlingh Onnes in Leiden in 1911 when he discovered that all electrical
resistivity of mercury miraculously disappeared at a temperature of 4K. For a
long while it was thought that superconducting compounds kept the same
properties as normal metals, i.e. are magnetic, when the Meissner effect came
about in 1933.  A definition of the
Meissner effect is that when a material transitions between the normal and superconducting
phases it expels all magnetic fields. (1) Despite this, full understanding of
the spectacle was not known by scientists until around the 1950’s.  The definition of superconductivity is the
phenomenon of exactly zero electrical resistance and expulsion of magnetic flux
fields when cooled to its critical temperature TC. This is different to perfect conductivity where
magnetic flux does not tend to be expelled. (2) Superconductors have the
potential to be very advantageous, however their remarkably low critical
temperatures often limit their ability to be used. Raising the critical
temperature or finding new superconductors with higher critical temperatures
would be particularly beneficial.
Intercalation is the reversible process of inserting a molecule, atom or ion
between the layers in a crystal lattice. This is often done to change the
properties of a molecule or increase/improve the favourable properties it
already possess’, in this case in combination with increased pressure it allows
superconductivity of FeSe at a much higher critical temperature. (3)
Structure of FeSe:
Iron based superconductors were only recently discovered in 2008 and are
similar to the better known cuprate superconductors in their
quasi-two-dimensional crystal structure. However unlike cuprates, the layers in
FeSe are thought to be the reason the compound has the ability to be a
superconductor as seen in Fig.1. FeSe alone has the TC ? 8K and it
was one of the earlier Iron based superconductors discovered as a PbO structure
type tetrahedral compound. Research has shown that an excess of Fe in the
compound is beneficial to maintaining the stabilisation of the crystal
structure, but the correct stoichiometry is vital to maintaining
superconductivity. (4)
 Fe in interstitial places?? (4)
Common elements/metals
FeSe is intercalated with??

Preparation Techniques:

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For You For Only $13.90/page!


order now

One type of superconducting FeSe is
Barium intercalated FeSe. In order to prepare this ?-FeSe needs to ne
synthesised first. One way of doing this is to add Fe and Se, in powder form,
to a mini mill Pulverisette in order to combine them. The pulverisette uses a
centrifugal force as well as a grinding wall to compound the two elements. The
powder product from this can then be pressed into a pallet and vacuum-packed into
a quartz tube which is annealed at   ?1000
°C for around 48 h. Following this the compound is quenched to 410 °C and
tempered for a further 100 h. Ice water is used to quench the compound to form ?-FeSe
and a very small amount of ?-FeSe as a side product. A Schlenk-line can be used
to intercalate other elements, in this case Barium, into the FeSe compound. The
reaction can take place in an ammonia filled line and an Ar occupied glove-box.
Dry ice would then be used to condense NH3 (l) and evacuation and
purification techniques are then used to prepare the apparatus. Two reactions
can take place in order to produce the desired material, one at low temperature
and one at room temperature.
The low temperature reaction can occur in a round bottom flask where a stoichiometric
amount of Ba is added to an amount of ?-FeSe in a solvent. Reaction completion and
solvent removal can take up to 12 h then the product can be dried in a vacuum,
after which X-ray diffraction analysis can be used to determine the correct product
was synthesised.
At Room temperature ?-FeSe powder and a stoichiometric amount of Ba can be
placed in a glass container together with a glass stirrer, the schlenk-line was
evacuated and NH3 (l) would be condensed in the same manner as
above. The reaction mixture would be left stirring at RT for up to 4 days. The
final product can again be analysed by X-Ray Diffraction, in this case and for
Low temperature synthesis the approximate unit cell parameter of the
tetrahedral Ba intercalated FeSe is    ? 8.5 Å. (7)

Another
type of superconducting FeSe that has been recently ascertained is alkali metal
– organic solvent intercalated FeSe that has a Tc ? 45 K. ?-FeSe
itself can be synthesised from high grade powder forms of Fe and Se, in the way
described above for the synthesis of Ba intercalated FeSe. The general formula
of the desired intercalated compound is Ax(C5H5N)yFe2-zSe2
where A = Li, Na, K or Rb.
For the intercalation synthesis a pre-ascertained amount of FeSe would be
combined with an amount of alkali metal dissolved in anhydrous pyridine   ? 0.2 mol dm-3. The reaction
happens at 40 °C and completion can be distinguished upon discolouration of the
solution

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