Chemistry Reference
In-Depth Information
-(BEDT-TTF)
2
IBr
2
salt,
P
1,
a
Figure 1.21. (a) Crystal structure of the
β
=
54
◦
.
Crystallographic data from Williams
et al.
, 1984. (b) Crystal structure of the
κ
79
◦
,
97
◦
,
0
.
659 nm,
b
=
0
.
897 nm,
c
=
1
.
509 nm,
α
=
93
.
β
=
94
.
γ
=
110
.
-(BEDT-TTF)
2
Cu[N(CN)
2
]Br salt,
Pnma
,
a
=
1
.
287 nm,
b
=
2
.
954 nm,
c
=
0
847 nm. Crystallographic data from Geiser
et al.
, 1991. C and S atoms are
represented by black and medium grey balls, respectively.
.
another in the
ac
-plane, resulting in a donor sheet. The insulating layer is formed by
arrays of Cu[N(CN)
2
]Br anions exhibiting a planar polymer-like structure (Geiser
et al.
, 1991). From these figures it can be again observed that the crystals are com-
posed of well-defined organic/inorganic interfaces. Such interfaces can be chem-
ically manipulated by the introduction of neutral guest molecules thus modifying
the electronic structure, phase diagram and electronic instabilities (Deluzet
et al.
,
2002a) and will be discussed in Section 6.4.
Nowadays much effort is dedicated to the study of superconductors under higher
hydrostatic pressures and under high magnetic fields. Above 5 GPa, the Fabre
salt (TMTTF)
2
PF
6
becomes a superconductor with
T
c
1.4-1.8 K (Adachi
et al.
,
2000), being the first example of a superconducting BFS sharing the same an-
ion. The case of
-(BEDT-TSF)
2
FeCl
4
is quite remarkable: upon application of
magnetic fields exactly parallel to the conducting layers superconductivity is in-
duced for fields
B
λ
1 K (Uji
et al.
, 2001). This experimen-
tally observed field-induced superconducting state survives between 18 and 41 T
(Balicas
et al.
, 2001), so that the well-known fact that the superconducting state is
destroyed for sufficiently strong magnetic fields, the so-called critical field
B
c
,is
>
17 T with
T
c
0
.
