J Supercond Nov Magn
DOI 10.1007/s10948-014-2617-x
ORIGINAL PAPER
Enhanced Magnetic Properties in Cu
0.5
Tl
0.5
Ba
2
Ca
2
Cu
3
O
10-δ
Superconductor Doped with Carbon
Nanotubes
M. Aftab Rafique · Sadaf Aziz · Najmul Hassan ·
Nawazish A. Khan
Received: 16 April 2014 / Accepted: 30 June 2014
© Springer Science+Business Media New York 2014
Abstract Fluctuation-induced conductivity (FIC) analysis
in the critical fluctuation region (cr), three-dimensional
(3D), two-dimensional (2D), and zero-dimensional (0D)
regions is reported for undoped and carbon nanotubes
(CNT)-doped Cu
0.5
Tl
0.5
Ba
2
Ca
2
Cu
3
O
10-δ
(CuTl-1223)
superconductors. Samples were synthesized by well-known
solid-state reaction method by adding CNT up to 7 wt %.
The X-ray diffraction data confirms the single-phase
orthorhombic structures following PMMM space group
for all the samples. The scanning electron microscope
(SEM) images reveal that the carbon nanotubes are present
in the spaces between the grains and connect the grains
electrically to help the intergranular current flow. From
FIC analysis, it was found that the width of critical and
3D regimes are shrunken with the increased CNT doping
in the final compound. Also, the coherence length (ξ
c(0)
),
the Fermi velocity (V
F)
, and the coupling constant (J)
are suppressed with increased CNT doping except for the
0.25 wt % doped sample. The decrease in important super-
conductivity parameters most likely arises due to low CNT
doping which indeed functions as columnar defects that
are produced by heavy ion irradiation. In this analysis, we
also found that the critical magnetic fields (B
c(0)
, B
c1(0)
)
and critical current density (J
c(0)
) were found to increase
with increased CNT concentration. These observations
suggest that addition of CNT (efficient pinning centers) to
M. A. Rafique · S. Aziz · N. A. Khan
Materials Science Laboratory, Department of Physics,
Quaid-i-Azam University, Islamabad 45320, Pakistan
N. Hassan ()
Department of Physics, Hazara University, Mansehra,
KPK, Pakistan
e-mail: najamalhassan@yahoo.com
CuTl-1223 compounds improve the electrical connec-
tion between the superconducting grains to result in the
improvement of magnetic properties of the final compound.
Keywords Superconductors · Chemical synthesis · X-ray
diffraction · Magnetic properties
PACS codes 74.70.-b · 74.72.Jt · 74.62.Bf
1 Introduction
The fluctuation-induced conductivity (FIC) in oxide high-
temperature superconductors (HTSC) arises due to their
short coherence length, high anisotropy, and low carrier
densities. There is a finite probability of Cooper pair for-
mation well above the critical temperature, T
c
, which in
turn causes the excess conductivity, σ
(T)
, and therefore
FIC which is referred to play a key role to investigate
the microscopic properties of HTSC. The formation of
the Cooper pair above T
c
is local. At T = T
c
, a steady-
state generation rate of the Cooper pair formation becomes
dominant over its decay rate and electrical resistance of
the material drops to zero [1–5]. This excess conductiv-
ity σ
(T)
is experimentally determined by the following
expression [6, 7]:
σ
(T)
=[ρ
N(T)
- ρ
(T)
/ρ
N(T)
ρ
(T)
] (1)
Here, ρ
(T)
is the measured resistivity and ρ
N(T)
= α + βT
is the extrapolated resistivity at zero K ; α is the resistiv-
ity at zero K , and β is slope of the line. Theoretically, the
excess conductivity is explained by the Aslamazov-Larkin
(AL) model in thin film samples and by the Lawrence-