Researchers synthesized a new high T(sub c) 2-2-3 superconductor Y2Ba2Cu3O(8+delta) by a special preparation technique and characterized it by ac-susceptibility measurements. Diamagnetism and Meissner effect sets in at low fields and superconducting transition onsets at 90 K. The systematic investigation of the real and imaginary components of ac-susceptibility as a function of temperature and applied ac magnetic field reveals that the magnetic behavior is that of a granular type superconductor

Baldha, G. J.

Joshi, H. H.

Joshi, S. M.

Jotania, R. B.

Kulkarni, R. G.

Mohan, H.

Pandya, H. N.

Pandya, P. B.

English

NASA Technical Reports Server

N92-21625
SUPERCONDUCTIVITY IN 2-2-3 SYSTEM Y2Ba2Cu2Os+ 8
H.H. JOSHI, G.J. BALDHA,, R.B. JOTANIA, S.M. JOSHI, H. MOHAN,
P.B. PANDYA, H.N. PANDYA and R.G. KULKARNI
Department of Physics, Saurashtra University
RAJKOT-360 005, INDIA
We have synthesized a new high-Tc 2-2-3 superconductor Y2Ba2Cu308+_ by
a special preparation technique and characterized It by ac-susceptibility measure-
ments. Diamagnetism and Meissner effect sets in at low fields and supercon-
ducting transition onsets at 90 K. The systematic investigation of the real and
imaginary components of ac-susceptibility as a function of temperature and
applied ac magnetic field reveals that the magnetic behaviour is that of granular-
type superconductor.
INTRODUCTION
In general, in the high-Tc granular bulk superconductors it is necessary to
distinguish between the superconducting properties of unconnected "grains" and
the "bulk" of grains connected through Josephson junctions. AC susceptibility
measurements as a function of temperature and magnetic field allow observation
of this double behaviour.
No attempt has been made to synthesize and observe superconductivity in
2-2-3 type systems except for our most recent communication (1) of superconduc-
tivity in a new 2-2-3 type system Y2Ba_ sCaosCU3Os÷ s by ac-susceptibility and
resistivity measurements. In this paper, we repo_ the synthesis and the charac-
terization of another new 2-2-3 superconductor Y2Ba2Cu3Os+s. Superconductivity
in Y2Ba CUoOo÷, (2-2-3) was identified by the systematic measurements of the real
and im_gin°ary [lossy) components of ac-susceptibility as a function of temperature
and applied ac field.
EXPERIMENTAL
Samples of nominal composition Y Ba Cu O÷ were prepared from the2 2 3 88
appropriate amounts of the finely ground mixed Y^O 3, BaCO 3 and CuO (all 99.9%
purity). The mixed powders Were pressed into pellets of 1-cm diameter and .2-cm
thickness under a pressure of 25 KPSi. We have devised a special technique of
sample preparation known as rapid thermal processing (RTP) treatment which is
described in detail elsewhere (2). According to this technique 2-2-3 pellets were
introduced in a preheated furnace at 950"C and fired for two hours in closed
condition. Then the top of the furnace was opened to air for half an hour at 950°C
and the samples were rapidly cooled to room temperature. The cooled samples were
recycled once more as above. Thus, 2-2-3 samples require two-step processing.
X-ray diffraction data were obtained at room temperature using a Philips PW1820
powder diffractometer with FeK(_ radiation. X-ray diffraction (Fig. 2) showed single
phase for 2-2-3 samples. The real (X') and imaginary (X") components of the ac-
susceptibility of a sintered Y2Ba2Cu3Os. s were measured as a function of tempera-
ture (4.2K to 128K) for different ac field amplitudes {24A/m to 2400A/m or 0.30e
149
https://ntrs.nasa.gov/search.jsp?R=19920012382 2020-03-17T13:08:46+00:00Z
to 30 Oe) at a frequency of 100Hz. In these measurements the samples were first
zero-field cooled to liquid helium temperature and then measured in applied ac
fields during the warming run.
RESULTS AND DISCUSSION
All observed X-ray powder diffraction peaks of Y, B ahCUoOs. 8 can be ac-
counted for by an orthorhombic unit cell of a=4.0314 (i 1_/_, B=_.7202 (8)/k and
c= 13.338 (5) A crystallographically. The observed X-ray diffraction pattern of this
new superconducting compound is compared with the corresponding computer X-
ray diffraction spectra obtained employing the refined unit cell constants and the
atomic fractional coordinates assuming space group symmetry Pmmm. A very
good agreement is found between the observed and computed X-ray spectra
confirming that the atomic arrangement is of a simple perovskite-type belonging
to the orthorhombic Pmmm space group. From a comparison of lattice parameters
of 1-2-3 (3.4) with the present 2-2-3, it is evident that a and c parameters have
respectively increased by 0.21/_ and 1.68 A. Moreover, the unit cell volume of 1-
2-3 is 173.7 A 3 (3.4) and that of 2-2-3 is 200.2 A 3. These observations indicate that
the excess "Y" in 2-2-3 is responsible for the expansion of the unit cell and possibly
additional "Y" is located along the c axis. The temperature dependence of both the
real (X') and imaginary (X") of the ac-susceptibility data measured at 100Hz and
in applied ac fields 0.3 Oe, 3.0 Oe and 30.0 Oe is shown in Fig. 2. As observed from
X'(T) data in Fig. 2, the sample Y2Ba_CuaOsa exhibits diamagnetism and Meissner
effect at low field 0.3 Oe, and the onset of superconducting transition starts at 90K.
For a perfect superconducting state, at the lowest applied field and at low
temperatures, X' and X" should attain values of -1 and 0, respectively, implying
complete diamagnetic shielding and the absence of any losses due to the trapped
flux.
In the present case, at 0.3 Oe (low field) and at 4.2K (low temperature), X' and
X" achieve values of -0.92 and 0.007, respectively, implying 92% diamagnetic
shielding and slight imperfect diamagnetism below Tc. With increasing tempera-
ture at 0.3 Oe, X' changes from -0.92 below Tc to a small positive value above Tc,
while the imaginary part, X", peaks at Tc and is practically zero above and below
Tc. Both X' (T) and X" (T) are sensitive to the ac-applied fields and thus can give
significant insight into the role of microstructure on the superconducting proper-
ties of these new high-Tc oxide sintered materials.
It is evident from Fig. 1 that as the ac-applied field is increased to 240 A/m
(eOe), X' reduces to 85% diamagnetic shielding, while the X" exhibits a slight peak
at Tc in addition to a major broadened peak at about 40K. These features indicate
two contributions to the susceptibility of the material; one very sensitive to
measuring field and the other, relatively insensitive to field (5,6). On the other
hand, for moderate fields like 0.3 Oe (Fig. 1), the two contributions to the
susceptibility are not separable or it is sufficient to supress one of the contributions
near Tc at this field. These observations suggest that the investigation of the
magnetic field dependence of ac susceptibility is a particularly useful method for
separating the two contributions. Further increase in ac-applied field to 2400 A/
m (30 Oe), X' reduces to 45% diamagnetic shielding and X" again shows a peak near
Tc along with very broad indication of peak. Also note that the lossy component X"
which should ideally be zero for the superconducting state is rather large and
positive at liquid helium temperature at fields above 30e. This is unusual if the
150
material was indeed a bulk superconductor. These observations indicate that a sig-
nificant amount of flux indeed penetrates through the system even at low fields,
and that in fields above 30 Oe, one essentially is looking at the intra-granular
superconducting properties. The "two-stage" ac-susceptibility behaviour can be
explained as arising from two contributions to the susceptibility; one of which is
intrinsic to the superconducting grains, and the other originating from the network
that links the grains weakly.
In conclusion, we have prepared and identified a new high-Tc superconduc-
tor Y2BahCUaOa÷8 (2-2-3) by at-susceptibility measurements. The systematic
investigation of the real and imaginary components of ac-susceptibility as a
function of temperature, applied field and frequency reveals that the magnetic
behaviour is that of a granular-type superconductor in which "strongly" supercon-
ducting grains are coupled via weak superconducting links.
ACKNOWLEDGEMENTS
The authors are thankful to Prof. K.V. Rao, Department of Solid State
Physics, Royal Institute of Technology, Stockholm, Sweden, for extending experi-
mental facilities. This work was financially supported by University Grants
Commission, New Dehli.
REFERENCES
i. KULKARNI, R.G., G.J. BALDHA, H. MOHAN, R.B. JOTANIA, and H.H. JOSHI,
"New High-Tc 2-2-3 type Superconductor Y2Ba_ sCao.sCua08._," Solid State Com-
mun. (in press), 1990.
2. KULKARNI, R.G., "Synthesis and Crystal structure of the High-Tc Supercon-
ductor Y2BaLsCao.sCUaOs÷s, '' J. Master. Sci., 1990.
3. CAVA, R.J., B. BATLOGG, R.B. VAN DOVER, D.W. MURPHY, S. SUNSHINE, T.
SIEGRIST, J.P. RAMEIKA, E.A. REIRMAN, S. ZAHURAK, and G.P. SPINOSA, Phy.
Rev. Lett., 58, 1676 (1987).
4. TARASCON, J.M., W.R. McKINNON, L.H. GREENE, G.W. HULL, and E.M.
VOGEL, Phy. Rev., 1336, 226 (1987).
5. GOLDFARB, R.B., A.F. CLARK, A.I. BRAGINSKI, and A.J. PANSON, Cryogenics,
27, 475 (1987).
6. CHEN, C.X., J. NOFUES, N. KARPE, and K.V. RAO, Kexue Tongbao, 33, 560
(1988).
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153



Superconductivity in 2-2-3 system Y2Ba2Cu2O(8+delta)

Superconductivity in 2-2-3 system Y2Ba2Cu2O(8+delta)

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