PHYSICAL REVIEW B
VOLUME 48, NUMBER 17
1
NOVEMBER 1993-I
Evidence for the revival of superconductivity in Nd162Ceo 1sCuo4
by doping with divalent alkaline-earth elements
Department
Okram G. Singh*
of Physics, Indian Institute of Technology, Powai, Bombay $00076, India
Om Prakash
Materials Science Centre, Indian Institute of Technology,
Department
Pomai, Bombay $00076, India
B. D. Padalla
of Physics, Indian Institute of Technology, Powai, Bombay $00076, India
Anant V. Narlikar
Delhi 110012, India
National Physical Laboratory, Hillside Road,
(Received 3 May 1993; revised manuscript received 9 June 1993)
¹m
The revival of superconductivity in the electron-excess T'-type compound Nd&. 8&Ceo. ysCu04
by hole doping has been observed. The normal-state resistivity (p) changes from semiconducting
(dp/dT
0) to metallic (dp/dT )0) as the hole doping increases up to a certain level.
(
In Nd2 Ce Cu04 s (Nd2Cu04 or T' type) c-ompounds, prepared in reducing atmosphere, it is found
that Ce exists predominantly in the 4+ state. This indicates electrons as the majority charge carriers in the system. If electron population exceeds some critical limit
due to increase in Ce content, the compounds become
' It appears that disappearance
of
nonsuperconducting.
superconductivity in these compounds is associated with
excess electron population. If it is so, doping the system suitably with holes (using a divalent ion) should result in the revival of superconductivity.
Moreover, such
an approach, if it works, should enable one to control
the electron population to optimum level for best superconductivity behavior of the material. In order to establish this, we synthesized electron-doped compounds,
Ndy 82 ~M Cep ysCu04 g, x & 0.09 and M=Sr, Ba, or
Ca. These compounds showed T'-type structure, and
resistance (Rz /Rsoo) vs temperature (T) measurements
con6rmed the revival of superconductivity with x & 0.
The samples of Nd~ 82 Sr Cep. isCu04 g, x= 0, 0.02,
0.03, 0.06, and 0.09 were prepared by ceramic solidstate reaction. Proportionate quantities of CuO, Ce02,
Nd203, and carbonate of Sr were finely mixed and calcined in air at 950 C for 15 h, and pulverized, pressed
into pellets, and sintered in air at 1135 'C for 15 h. The
samples were then quenched in air to room temperature,
followed by annealing in high purity argon at 1000 C for
15 h and quenched.
X-ray-diffraction
(XRD) analysis has revealed the
formation of T'-type structure for x & 0.09. Typical XRD patterns
for x=0.00 and 0.06 in the
Ndq 82 Sr Cep qsCu04 g are shown in Fig. 1. Some additional weak peaks, corresponding to a trace Nd203 impurity phase, appear in the XRD patterns of a few samples. The computed lattice parameters are: a =3.9515(3)
c = 12.083(2) A. for x=0.00 and a=3.9478(1) A. ,
c =12.075(l) A for x=0.06. No significant changes in
the lattice parameters, a and c, are observed for other
Sr doped -compositions (x & 0.09).
Although the present samples are prepared in argon
atmosphere, the constituents are similar to those of the
T' compound. It is, therefore, desirable to check if the T*
phase is present in these samples. For this purpose, we
have compared the XRD patterns of these samples with
those of the T' compound. No evidence for the presence
of T* is found. This result is as expected, since the
lattice parameters for T* are characteristically difFerent
from those of T'. '
0163-1829/93/48(17)/13182(2)/$06. 00
13 182
48
CuK&
~d).S&-x S"x Cep ~8CuOg-S
C
Le
0
x=p
x =0.06
30
4,
50
0
8 (4egreps)
60
P
FIG. 1. XRD patterns of Nd~. sq Sr Ceo. qsCu04 h, x=0
and 0.06, revealing T'-type structure. For the x=0.06 sample,
very weak extra peaks appear which correspond to Nd203
trace impurity.
1993
The American Physical Society
EVIDENCE FOR THE REVIVALL 0
OF SUPERCONDUCTIVITY
48
1.5
Nd182 xSrxCe0.18Cu04 5
~dl, 76 M0. 06G 0.18
25—
1.
5-8
075
4.2
0.50
Pl
~
09 -/
06—
C)
0.3—
o
0 00
000
100
100
vs
T
150
T (K)
200
lots of Ndq
82
250
300
~Sr~ e p ys Cu04
e 300K to
M =Baan
A q vs T plots (Fig. 2) for the samples of
. revea
Sr Cep isCu04 g, x
-".
ound ~x=0
as vanis hing
parent compoun
'
~the
'»)
normal-state resistivi
tivit y behavior
e
changes
y; ,~~ii&
-':.
'-, ---d---
x from
rom semiconducting i e
x & 0.03, and the optimum
t
or
racters are obtained for
m tall andd suup ercon ucting
ch ara
ra
x=
=0..06 ) ('")
(ill the critical supercan uc mg ra
onset improves from
18 K for x=O to
23 K for x=0.06 an d the transition wi d t h (b, T) lik
oves and &iv~ the two superconductingn p hases
a
are
values o r concen r
present for low va
existss for x &
whereas, a sing
ingle superconducting
p ase exis
with
250
300
es of
o the TEP were
Moreover, the magnituudes
e allic character.
on sup erco nductivity in t is ami y
a.
s was also found to occur for M= a an
les for x=0 06 The preparation proe sam p les was similar o h a f M=S
t ese samples were a owe o
increasing
to metalliclike
h,
'clikee, d p&&~dT&0, behavior in the
The observed metallicli
normal-sta tee
resistivity
e ]8Cu04
u
Ndi 82 ~Sr Ceo
g is an in eres in
— pe superconT'-t
he p reviously Known
k
y
0) or a
200
electronlike.
E
)e
150
(K)
vs T lots of Ndq. q6Mp. p6Cep. ~sCu04
'
12 K.
C ain thee temperature range 300 K to
I
I
50
I
I
50
T
all
GU
M=Co
K'
2,6
025
=Oj~
13 183
M=Ba
100
I—
IN. . .
' 4' 7
eak metallic
((d p&/dT
'
'
)0) resistivity
'or.
behavior.
in g to note that these samp es, w e
™ p here, s owe semic
g atmos
e
Further, the negative sign o
ower (TEP), measure d on h e
moelectricic power
h
l
x=O and 0.09, revealed the majori it y ccharge
ar carriers to be
*Electronic address: : OKRAMCC.
IITB.ERNET. IN
OK
PHBDPIAQ CC. IITB.ERNET. IN
1197 (1989).
al.- (un p ublished).
g
Okram G. Sin
Ing h Om Prakash, B. D. Pa a xa,
and L. C. Gupta, Supercond.
drasekharam, A. S. Tamhane, an
show the
M =Ba.
T
onset
21 K for M
=
a an
effective
t s t u dies
i
clearly show
of the presen
The results
p
in
eelectron-excess
ec r
of
su p erconductivity
revival
o doping, using
uO g compoun d b y hole
Ndi. 82Ceo. j SCu04
con-earth eelements, w h'ich essentially
esse
divalent alkaline-ear
It is evident
e electron popu ation.
trois the
do in level increases, thee system of
(itinerant) electrons makes the matena con
superconductivi y. 8
o e doping in the
we have shown t h att hole
In conclusion, w
— ypee compoun
T'-t
superconducrevives su
electron-excess T
'
tivity. This reve aation is likely to l ea d too tailoring of
to
an is expected
su erconducting systems s and
new oxide supe
exp
provi e a c1ue to the mechanism o f hiig h temperature superconductivity.
th
. A arwal, V. P. S. Awana, V. N. MoorK. Suba, an d D. Chandrasekharam for h
ents. This work was supporte d b y g rantp
om
in-aid for researc in sup
su erconductivity
e
ment of Science and Technology, New Delhi.
. 5 561 1992).
Y. Tokura, H. Takagi, and S. Uc
i a,
a
3 . J. A l. Ph . 28, L49 (1989).
M. E. Lopez-Morale, R. J. Savoy, and . . ra
Res. 5, 2041 (1989).
I,.
un p ublished).
Ok am G. Sj.ngh et a.
E. A. Early, C. C. Almasan, R. F. 3ardim, an
Phys. Rev. B 47, 433 (1993).