Overall, – show graph. Going down the group


Overall, the structure, synthesis and the cause of
superconductivity in A3C60 has been researched thoroughly
and explained. Further research will be done into what the A3C60
superconductors can be used for, as they aren’t being used commercially or in
other cases. However, C60 has multiple applications since it’s a carbon
cage that can carry a range of molecules. Apart from its use in nanotechnology
and materials science, it’s used a lot in the medical industry as photosensitisers,
antioxidants and a drug delivery system 7.









XRD patterns taken of C60 and K3C60
showed that K3C60 had a slightly smaller lattice
parameter than C60, as shown in fig.1. This would be because of the
Coulombic interaction between the K+ cations and the C60-
anions 10. As mentioned previously, there’s a correlation between
atom mass/size and Tc. – show
graph. Going down the group of alkali metals (group 1) atomic/ionic radius
increases, which increases the lattice parameter. This causes a decrease in the
width of the t1u band,
which increases the density of states at the Fermi level (N?F)
and causes Tc to increase 11, as shown in the equation
(1). Continuing this trend, Cs3C60 should have a higher Tc
than Rb3C60, but since Cs3C60 has BCC
packing instead of FCC packing, this cannot be confirmed.

Superconductors are diamagnets and repel external magnetic
fields when the superconductor is in a magnetic field – this is called the
Meissner effect. The A3C60 systems are type 2
superconductors, which means that it has two critical fields and two transition
temperatures. When T>Tc1 (lower critical field temperature) the external
magnetic field can penetrate the material, but it still remains a
superconductor. When T>Tc2 (higher critical field temperature)
then the material switches from superconducting to non-superconducting.

The superconductivity is explained by BCS
(Bardeen-Cooper-Schrieffer) theory because bound pairs of electrons (Cooper
Pairs) can move freely within the crystal lattice with zero electrical
resistance (Mcdonald, 2010) when T