LiFeAs Pnictide Superconductor a Simple Electrochemical Method of
Preparation
M.Kanuchova , M. Majoros ,J.Kanuch ,Y,Ding , M. D. Sumption , and E. W. Collings
1
2
1
3
2
2
1.Faculty of Mining, Ecology, Process Control and Geotechnology, Institute of Montaneous Sciences and Environmental Protection, The Technical University of Kosice, Slovakia Letn 9, 042 00 Koice,
Slovakia.
2.Center for Superconducting & Magnetic Materials (CSMM), Department of Materials Science & Engineering, The Ohio State University Columbus, OH 43210
3. Department of Physics, Southeast University, Nanjing 211189, P. R. China
E
E
RT
ln Q
nF
2LiCl (l) 2Li (s) + Cl2 (g)
+
Cathode (-): Li (l)+e Li(s)
Anode (+): 2Cl-(l) Cl2(g)
+2e
DC power supply
Cathode
-3
Fig. 4: A stereo microscope crosssection of the FeAs pellet with a
LiFeAs layer on its surface and its
magnified
view
(short
time
electrolysis).
e-
Anode
2.5 10
2 10
-3
5 10
2.5 10
UAR UAC
Ubub
Cl-
-1 10
ZFC
FC
-3
1.5 10
-3
-3
1 10
-4
5 10
-1.5 10
-3
H = 100 Oe
0
a
-2 10
-3
0
5
10
15
20
25
Fig.
5b:
Magnetic
moment vs. temperature
of
the
LiFeAs
film,
corrected
on
ferromagnetic
background due to unreacted FeAs in the
sample. Estimated Tc =
17 K.
2 10
-3
1 10
T = 17 K
5 10
-4
H = 100 Oe
Electrolyte
0 10
UCC
Cathode
Fig.3:Components
of the bath voltage
Ubath.
1 10
-4
-4
-4
0
5
10
15
20
25
30
8 10
-5
T (K)
Fig. 5a: DC
magnetic
moment vs. temperature
of
the
LiFeAs
film.
Estimated Tc = 17 K. The
magnetic
moment
of
LiFeAs
material
is
affected
by
a
superimposed
ferromagnetic moment of
unreacted FeAs in the
sample.
6 10
-5
5
10
15
20
25
30
35
40
-3
3.2 10
-3
3.15 10
-3
3.1 10
-3
3.05 10
-3
3 10
-3
0
5
10
15
20
25
30
35
40
T (K)
Fig. 7: DC magnetic
moment in heating and
cooling at Ha = 100 Oe
followed by zero-field
warming (diamonds
green) (another sample
prepared by the same
method).
9 10
-6
8 10
-6
7 10
-6
6 10
-6
5 10
-6
4 10
-6
3 10
-6
2 10
40
-6
-4
a
0
R ()
R () (T>20K) - lin. fit
Fig.
8:
R(T)
dependence
in
cooling
at
zero
applied
magnetic
field
(the
same
piece of pellet as in
Fig. 5).
M'' - heating
M'' - cooling
-4
1 10
5
Temperature (K)
30
T (K)
2 10
-3
R ( )
-5 10
-4
M' - heating
M' - cooling
c
Ubath Ecell
Fig 1 Schematics of the
electrochemical method
of
LiFeAs
preparation
from
molten
LiCl
electrolyte at 610oC in
open air (FeAs cathode,
inert
electrode
(e.g.
stainless
steel
or
graphite) anode).
1 10
-3
a
2 10
0
M ' (emu)
Li+
3.25 10
-3
a
1.5 10
heating - Ha=100 Oe
cooling - Ha=100 Oe
heating - Ha=0
-3
Conclusions
H = 100 Oe (dc)
Anode
3.3 10
B =0
ZFC
FC
-3
-4
m (emu)
m (emu) (corrected on ferromagn. background)
3 10
10
15
20
25
30
35
M '' (em u)
Unlike the known isoelectronic undoped
intrinsic FeAs compounds, LiFeAs does not
show any spin-density wave behavior but
exhibits
superconductivity
at
ambient
pressures without chemical doping. It has a
superconducting transition temperature, Tc ,
of 18 K with electron-like carriers and a very
high 0 K upper critical magnetic field, Bc2(0),
of greater than 80 T making the compound
suitable for many high magnetic field
applications
at
cryogenic
temperatures.
Oxypnictide materials are known for a
complexity of their methods of preparation.
The reported methods of LiFeAs preparation
are based on the solid-state reaction at high
temperatures (740-1050 oC) for long times (24
60 hours). In the present work a simple
electrochemical route is proposed for the
preparation
of
a
pnictide
LiFeAs
superconductor. During electrolysis Li ions in
the electrolyte become inserted into the FeAs
lattice to form LiFeAs on the surface of the
FeAs electrode. The proposed method differs
from the existing electrochemical method (N.
Chen, et al, J. Appl. Phys., Vol.107, pp 09E123,
(2010) and also from the traditional high
temperature solid-state reaction methods. It
is promising for the preparation of LiFeAs
0
bulks and large scale LiFeAs films or tapes for
cell
cell
various electric
power or high magnetic field
applications at cryogenic temperatures.
Materials & Methods
Fig. 2: x-ray of FeAs (a powder
obtained by grounding the pellet)
used as a cathode. Experimental
peaks (top of the figure) agree well
with the FeAs data base peaks
(bottom of the figure).
m (emu)
Abstract
Temperature (K)
Fig. 6: AC magnetic moment
(M and M) vs. temperature
in heating and cooling at 100
Oe applied dc magnetic field
(a different piece of the
same pellet shown in Fig. 5).
Estimated Tc = 15 K.
A successful preparation of LiFeAs
film using a simple electrochemical
method has been presented. The
method is simple and easy to employ.
Unlike the previous one it does not
need a Li anode and it works in open
air, which makes it suitable for
practical applications. Given the fact
that Bc2 of this material is about 80 T
at 4.2 K makes it attractive for high
magnetic field applications. A further
improvement of the method is
possible. The work is in progress.
