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Part $2 - Superconductivity 1: LTS - Special superconductors, etc.
P r e s s u r e - i n d u c e d s u p e r c o n d u c t i v i t y o f iodani l
Tatsuya Yokota ~ Nao Takeshita', Katsuya Shimizu ~ Kiichi Amaya', Akifumi Onodera ~ Ichimin Shirotani b
and Shoichi Endo ~
"Faculty of Engineering Science, Osaka University, Toyonaka, Osaka 560, Japan
bMuroran Institute of Technology, Muroran 050, Japan
CResearch Center for Ultra Science, Osaka University, Toyonaka, Osaka 560, Japan
The electrical resistance and the crystal structure of an organic molecular crystal of iodanil C614Oz are studied. The
crystal is found to become metallic and to transform to amorphous slate under pressures above 30GPa. At temperatures
around 2K, the onset of superconductivity is observed under pressure of 52GPa.
1.INTRODUCTION
The crystal structure of iodanil (C~I402) is
monoclinic and belongs to space group P2~/C with two
molecules in a unit cell. The crystal is an insulator at
ambient pressure but expected to become a metal under
pressure. Electrical resistance of iodanil was measured
at room temperature by Onodera el alJ ~) and the
resistivity of 5• was observed at the
estimated highest pressure of 25GPa. In the present
experiments, we measured temperature dependence of
the resistance as well as the X-ray diffraction under
pressure so as to study the metallic state in detail.
2.RESULTS
The iodanil crystal used in the experiments was
prepared by the reaction of bromanil with potassium
iodide and recrystallized from ethyl acetate. The
pressures are generated by a clamp type diamond-anvil
cell made of nonmagnetic hardened BeCu alloy. The
sample and the nonmagnetic stainless gasket was
insulated by AlzO 3 fine powder mixed with epoxy. The
app!ied pressure was determined by ruby fluorescence at
liquid nitrogen temperature. The sample temperature is
Czechoslovak Journal of Physics, Vol. 46 (1996), Suppl. $2
supposed to be given by tile Ge thermometer on tile
pressure cell which are cooled down to 90mK by
~He/4He dilution refrigerator.
10 lo
10 8
106
o 10 4
102
I I I I I I I
I0danil
�9 Loading
o Unloading
10o0 J , , , I , , 10 20 3 0 4 0
.P (OPa)
Figurel Pressure dependence of electrical resistance of
iodanil at room temperature.
817
Figure 1 shows the pressure dependence of the
resistance at room temperature. The resistance decreases
rapidly with increasing pressure. The decrease of the
resistance by several order of magnitude is observed at
the pressure range between several GPa and 35GPa.
There are no abrupt change suggesting a insulator-metal
transition.
Figure 2 shows the temperature dependence of the
resistance. We observed that the sign of dR/dT changes
from negative to positive at pressure around 30GPa and
iodanil behaves like metallic at higher pressures. The
resistance decreases with decreasing temperature in
proportional to temperature above 50K and gradually
approaches to the residual values at liquid He
temperature region.
1.21
1.1
1
0.9
| ! i i i I i i
Iodanil
36GPa
I ! I I ! I I
0 20 40 60 T(K)
Figure 2 Temperature dependence of electrical resistance of
iodanil tot fixed pressures around 30GPa.
We tried X-ray analysis of iodanil under pressure
and found that Ihe diffraction peaks observed at low |
pressures shifts continuously and becomes weak with
increasing pressure. Finally, at 30GPa, all the peaks
disappears, suggesting the transformation to amorphous
stale. This anmrphous stale is found to be quenched by
reducing pressures.
Figure 3 shows the resistance as a function of '
818
temperature at 52GPa. The small drop of the resistance
at 2K is considered to be the onset of superconductivity.
The finite resistance appearing at temperature below
0.5K depends on the pressure as well as sampling. This
residual resistance may come from the crystal
imperfections caused by the uniaxial stress.
160
o ~" 140
120
0
i I I I
/ Iodanil P ~ 5 2 G P a
J 1 , , ! , I , I
2 4
r(K)
Figure 3 Temperature dependence of electrical resistance of
iodanil in pressure of 52GPa.
3.CONCLUSIONS
Electrical resistance measurements of a simple
organic molecular crystal of iodanil are performed down
to low temperatures of 90mK and under high pressure
up to 52GPa. At about 30GPa, the resistance shows
metallic temperature dependence and also the crystal
transform to alnorphous stale. The onset of
superconductivity is observed at 2K in pressure of
52GPa. The study of the X-ray diffraction in the
measured highest pressure and the detection of the
Meissner effect are now going on.
REFERENCES
~)l.Shirotani, A.Onodera, Y.Kamura, H.Inokuchi and
N.Kawai,J.Solid Stale Chem.18(1976)235.
2)A.Onodera, I .Shirotani , H. lnokuchi and
N.Kawai,Chenl.Phys.Lett.25(1974)296.
Czech. J. Phys. 46 (1996), Suppl. S2
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