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Structural and superconducting properties of the system La1−xPrSrxCuO4
PHYSICA
Physica C 182 ( 1991 ) 149-152 North-Holland
Structural and superconducting properties of the system
Lal _xPrSrxCuO4 D.G. K u b e r k a r , A.K. Rajarajan, G e e t h a Balakrishnan ~, L.C. G u p t a and R. V i j a y a r a g h a v a n Tata Institute o f Fundamental Research, Homi Bhabha Road, Bombay 400005, India Received 1 August 1991
Structural and superconducting properties of La~ _xPrSr~CuO4 have been investigated. Substitution of Sr for La in LaPrCuO4 (T'-structure), induces a transformation to the T-structure unlike in LaSmCuO4 and LaGdCuOa where a transformation takes place from the T ' - to the T*-structure. The transformation gets completed at x = 0.2. These studies suggest that the rare earth ionic size is critical in the T' ~ T (T*) transition. Superconductivity is observed in samples with 0.1 < x_< 0.25.
1. Introduction RR'CuO4 cuprates generally crystallize in three structures, namely, T, T' and T*, depending upon the nature of the rare earth ions R and R' [1]. La2CuO4 stabilizes in the distorted T-phase, whereas many members of the series R2CuO4 such as Pr2CuO4 and Nd2CuO4 crystallize in the T'-phase. Usually materials having two rare earths R and R', lanthanum being one of them, stabilize in the T*-phase [2], which has combined features of the T and T ' phases. Superconductivity has been observed in systems belonging to all the three phases; for instance, Tc=36 K for Lal.85Sro.85CuO4_y (T-phase), To=21 K for Nd~.85Ceo 85CuO4_,, (T'-phase) and To=20 K for L a o . 7 5 S r o . 2 s S m C u O a _ y (T*-phase). Several studies have been reported [3,4] on the structural stability and superconducting properties in R 2 C u O 4 c u prates leading to valuable information with respect to the effect of the size of the rare earth ions and the role played by the substituent atoms in modifying the structural and superconducting properties of these compounds. La2_xPrxCuO4 undergoes a first order phase transition from orthorhombic to tetragonal T'-structure; the system transforming completely to the T'-strucPresent address: Department of Physics, University of Warwick, Coventry CV4 7AL, U K
ture for x > 0.75 [ 5 ]. Lattice constants of the tetragonal system LaPrCuO4 (x--1 ), for instance, are a = 3.966 and c-- 12.429. Many other materials of the composition LaRCuO4 (R = Pr through G d ) also stabilize in the T'-structure. Substituting trivalent La atoms, in these compounds, partially by divalent Sr atoms results in the transformation of the structure to T*-phase. The value of x, which leads to a complete transformation of the system Lat _xSrxPrCuO4 from the T ' - to the T*-structure depends upon the rare earth R. For instance, x = 0 . 1 5 and 0.17 for La~_xSrxNdCuO4 and LaL_xSrxSmCuO4, respectively. During the course of our work on materials Lal_xSrxRCuOn_.v, we realized that structural and superconducting properties of the system La~_xSr~PrxCuOn_y have not been investigated so far. The purpose of the present studies was to examine the effect of Sr-substitution for La on the structural and superconducting properties of La~ _ xSrxPrCuOa_y and compare them with those reported for other La~_xSrxRfuOa_.v systems.
2. Experimental Samples having composition La~_xPrSrxCuO4_y, 0.00-
0921-4534/91/$03.50 © 1991 Elsevier Science Publishers B.V. All rights reserved.
150
D. G. Kuberkar el al. / Structural and superconducting properties of La ,_ xPrSrxCuO4
Requisite quantities of the high purity (better than 99.99%) constituent oxides and SrCO3 were thoroughly mixed and heated at 950°C in air for ~ 18 h; the resulting material was ground and heated again at 950°C for another 18 h. For the final heat treatment, the material was pressed in pellets which were sintered in air at 1050°C for about 12 h. Structural investigations of the materials were carried out using X-ray diffraction while the superconducting properties were studied using AC susceptibility and DC four-probe resistivity techniques.
400
La PrCuo4 200
0 .--'-~ l 03
z
I z~
2oc-
Lao.gsPrSro.osCuo4
,,
,, ,,
(b)
zx
0
o
3. Results and discussion Loo.e PrSro.2Cuo4
X-ray diffraction patterns of the materials Lat_xPrSrxCuO4_y (x=0.00, 0.05 and 0.2) are shown in fig. 1. All the diffraction lines observed in the material LaPrCuO4 are indexed in terms of the T'-structure, which is consistent with the results reported in the literature. In the material with x = 0.05, there are two sets of diffraction lines; one of them contains lines (marked as * in fig. 1 ) which correspond to the T'-structure and the other set contains lines which can be indexed in terms of the T-structure. This suggests that the presence of Sr atoms induces a transformation T' ~ T in this system. Further increase in the Srocontent leads to an enhancement of the intensity of the lines corre-
2J2
0
t 29
i 56
i 45
2 e ----~
Fig. 1. XRD patterns of Lal_xPrSrxfuOa_y (x=0.00, 0.05 and o.2). sponding to the T-structure. Finally, in the sample with x=0.2, lines corresponding to the T-structure only are present in the X-ray diffraction pattern. This shows that the system is completely transformed from the T'- to the T-structure for x=0.2.
20 La i_xPrSrxCuO4_y
15-
oO°". . . . . ~•o°,,,, . . . . .
T 0 E itl L) Z
X=O.I °°•°o•••••oooo•oo•oe•o••eo•
I0-
e
X= 0.15
vvV v v v v v v v v v v vVV~ v vv v v v v v ~ v v v v v v 9vv v ~hr~tv v v V V V v vvq
5-
•
v
X=O.5
LtJ n," oo ° °
0
I o....
0
I0
~ c ~ o o o o oooooooo o0 o oaoooo o o oooo oooo ooOO oo oooo ooooooo o o ° 000°-9 ~v
V vZt
20
& & ~ &&&AAA&& AA~A&& & & & & ~ 4 &A & A A A 4 & ~ A A A & &&AA & & & 4 ~
,A •
t
50
I
I
I
I
50
40
50
60
TEMPERATURE
X=0"21 70
80
(K)
Fig. 2. Temperature dependenceof resistance of various Lal _,PrSrxCuO4_ysamples.
D. G. Kuberkar et al. / Structural and superconducting properties of La l_ xPrSrxCuO4
The temperature dependence of the resistivity of many samples La~_xPrSrxCuO4 has been measured and is shown in fig. 2. It is clear that as the Sr-concentration increases, the metallicity of the material also increases. The Lao.sPrSro.2CuO4 sample exhibits a maximum Tc~25 K. The variation of superconducting transition temperature as a function of Stconcentration has been plotted in fig. 3 which shows that Tc increases slowly with the increase in Sr-concentration up to x = 0 . 2 above which Tc starts falling down rapidly. This behaviour is very similar to that observed in the La2_xSrxCuO4 system. In table 1 are shown the crystallographic details and the values of Tc of various samples of the system Lal_xPrSrxCuO4. Figure 4 shows AC susceptibility, as a function of temperature, of various La]_xPrSrxCuO4 samples. It is evident from the figure that both the strength of the diamagnetic signal and Tc are maximum for the sample with x=0.2. Samples with x = 0 . 0 5 and 0.30 do not exhibit any diamagnetic response down to 12 K which implies that these samples either do not superconduct or their T~ is below 12 K. A very striking feature of the present work is that the system under investigation, La~_xSrxPrCuO4, exhibits a transition from the T ' - to the T-structure. Many other systems La~ _ x S r x R f u O 4 , that have been studied for their structural and superconducting properties, however, transform from T ' - to T*-struc-
30 La l _ x P r S r x Cu 0 4
o 20
10 I 0.0
0.1
I
I
o.z
0.3
10.4
Sr c o n t e n t (X) Fig. 3. Variation of Tc as a function of Sr-content for Lal _xPrSrxCuO4_r.
Table 1 Structural and superconducting properties of Lal_~PrSrxCu04 x
Phase
Tc (K)
0.0 0.05 0.1 0.15 0.2 0.25 0.3
T' T' + T T'+T T' + T T T T
21 24 25 17 < 12
50 Lal_ x P r Sr x CuOn_y
Oo o o
40
o
o
X=0.2
o
t
o X = O . 15
o
30
v X=O.I
o
A X= 0,25
o °e.
r"
xi
•
20
" X = 0.05
o o
v v
v
I0
<
o v
I A&
0
atO •
-IC 0
I I0
&
• q7
o •
0
AU6Q • ~ VdVoVal3~UO • ~VOe~Qe~IOVOVOO
I 20
151
I 30
OOm0~V ~
• ~IOv V V V V I
I 40
50
TEMPERATURE (K) 313Hz 50mV Fig. 4. Temperature dependence of AC susceptibility for La~ _=PrSrxCuO4_~ samples.
152
D.G. Kuberkar et al. / Structural and superconducting properties of Lat_xPrSrxCu04
ture. This shows that the nature of the transition (T'--,T or T'--,T*) critically depends upon the size of the rare earth ion R. Systems in which the difference in the radii of the rare earth atoms is larger than FLa--rpr transform to T*-structure.
4. Conclusion
We have investigated structural and superconducting properties of the system La~_xSrxPrCuO4. The system transforms, for x = 0.2, to the T-structure which must be contrasted with the situation in many other systems La~_xSrxRCuO4 which transform to the T*-structure. The system exhibits superconduc-
tivity for 0.1 < x < 0 . 2 5 , Tc being the highest ( = 2 5 K) for x=0.2.
References [ 1 ] T. Takayama-Muromachi, Y. Matsui, Y. Uchida, F. Izumi, M. Onoda and K. Kato, Jpn. J. Appl. Phys. 29 ( 1989 ) L2283. [ 2 ] Y. Tokura, A. Fujimori, H. Matsubara, H. Watabe, H. Takagi, S. Uchida, M. Sakai, H. Ikada, S. Okuda and S. Tanaka, Phys. Rev. B 39 (1989) 9704. [ 3 ] J.B. Goodenough and A. Manthiram, Physica C 157 ( 1989 ) 439. [4] Y.Y. Xue, P.H. Hor, R.L. Meng, Y.K. Tao, Y.Y. Sun, Z.J. Huang, L. Gao and C.W. Chu, Physica C 165 (1990) 357. [5] K.K. Singh, P. Ganguly and C.N.R. Rao, Mat. Res. Bull. 17 (1982) 493.
Physica C 182 ( 1991 ) 149-152 North-Holland
Structural and superconducting properties of the system
Lal _xPrSrxCuO4 D.G. K u b e r k a r , A.K. Rajarajan, G e e t h a Balakrishnan ~, L.C. G u p t a and R. V i j a y a r a g h a v a n Tata Institute o f Fundamental Research, Homi Bhabha Road, Bombay 400005, India Received 1 August 1991
Structural and superconducting properties of La~ _xPrSr~CuO4 have been investigated. Substitution of Sr for La in LaPrCuO4 (T'-structure), induces a transformation to the T-structure unlike in LaSmCuO4 and LaGdCuOa where a transformation takes place from the T ' - to the T*-structure. The transformation gets completed at x = 0.2. These studies suggest that the rare earth ionic size is critical in the T' ~ T (T*) transition. Superconductivity is observed in samples with 0.1 < x_< 0.25.
1. Introduction RR'CuO4 cuprates generally crystallize in three structures, namely, T, T' and T*, depending upon the nature of the rare earth ions R and R' [1]. La2CuO4 stabilizes in the distorted T-phase, whereas many members of the series R2CuO4 such as Pr2CuO4 and Nd2CuO4 crystallize in the T'-phase. Usually materials having two rare earths R and R', lanthanum being one of them, stabilize in the T*-phase [2], which has combined features of the T and T ' phases. Superconductivity has been observed in systems belonging to all the three phases; for instance, Tc=36 K for Lal.85Sro.85CuO4_y (T-phase), To=21 K for Nd~.85Ceo 85CuO4_,, (T'-phase) and To=20 K for L a o . 7 5 S r o . 2 s S m C u O a _ y (T*-phase). Several studies have been reported [3,4] on the structural stability and superconducting properties in R 2 C u O 4 c u prates leading to valuable information with respect to the effect of the size of the rare earth ions and the role played by the substituent atoms in modifying the structural and superconducting properties of these compounds. La2_xPrxCuO4 undergoes a first order phase transition from orthorhombic to tetragonal T'-structure; the system transforming completely to the T'-strucPresent address: Department of Physics, University of Warwick, Coventry CV4 7AL, U K
ture for x > 0.75 [ 5 ]. Lattice constants of the tetragonal system LaPrCuO4 (x--1 ), for instance, are a = 3.966 and c-- 12.429. Many other materials of the composition LaRCuO4 (R = Pr through G d ) also stabilize in the T'-structure. Substituting trivalent La atoms, in these compounds, partially by divalent Sr atoms results in the transformation of the structure to T*-phase. The value of x, which leads to a complete transformation of the system Lat _xSrxPrCuO4 from the T ' - to the T*-structure depends upon the rare earth R. For instance, x = 0 . 1 5 and 0.17 for La~_xSrxNdCuO4 and LaL_xSrxSmCuO4, respectively. During the course of our work on materials Lal_xSrxRCuOn_.v, we realized that structural and superconducting properties of the system La~_xSr~PrxCuOn_y have not been investigated so far. The purpose of the present studies was to examine the effect of Sr-substitution for La on the structural and superconducting properties of La~ _ xSrxPrCuOa_y and compare them with those reported for other La~_xSrxRfuOa_.v systems.
2. Experimental Samples having composition La~_xPrSrxCuO4_y, 0.00-
0921-4534/91/$03.50 © 1991 Elsevier Science Publishers B.V. All rights reserved.
150
D. G. Kuberkar el al. / Structural and superconducting properties of La ,_ xPrSrxCuO4
Requisite quantities of the high purity (better than 99.99%) constituent oxides and SrCO3 were thoroughly mixed and heated at 950°C in air for ~ 18 h; the resulting material was ground and heated again at 950°C for another 18 h. For the final heat treatment, the material was pressed in pellets which were sintered in air at 1050°C for about 12 h. Structural investigations of the materials were carried out using X-ray diffraction while the superconducting properties were studied using AC susceptibility and DC four-probe resistivity techniques.
400
La PrCuo4 200
0 .--'-~ l 03
z
I z~
2oc-
Lao.gsPrSro.osCuo4
,,
,, ,,
(b)
zx
0
o
3. Results and discussion Loo.e PrSro.2Cuo4
X-ray diffraction patterns of the materials Lat_xPrSrxCuO4_y (x=0.00, 0.05 and 0.2) are shown in fig. 1. All the diffraction lines observed in the material LaPrCuO4 are indexed in terms of the T'-structure, which is consistent with the results reported in the literature. In the material with x = 0.05, there are two sets of diffraction lines; one of them contains lines (marked as * in fig. 1 ) which correspond to the T'-structure and the other set contains lines which can be indexed in terms of the T-structure. This suggests that the presence of Sr atoms induces a transformation T' ~ T in this system. Further increase in the Srocontent leads to an enhancement of the intensity of the lines corre-
2J2
0
t 29
i 56
i 45
2 e ----~
Fig. 1. XRD patterns of Lal_xPrSrxfuOa_y (x=0.00, 0.05 and o.2). sponding to the T-structure. Finally, in the sample with x=0.2, lines corresponding to the T-structure only are present in the X-ray diffraction pattern. This shows that the system is completely transformed from the T'- to the T-structure for x=0.2.
20 La i_xPrSrxCuO4_y
15-
oO°". . . . . ~•o°,,,, . . . . .
T 0 E itl L) Z
X=O.I °°•°o•••••oooo•oo•oe•o••eo•
I0-
e
X= 0.15
vvV v v v v v v v v v v vVV~ v vv v v v v v ~ v v v v v v 9vv v ~hr~tv v v V V V v vvq
5-
•
v
X=O.5
LtJ n," oo ° °
0
I o....
0
I0
~ c ~ o o o o oooooooo o0 o oaoooo o o oooo oooo ooOO oo oooo ooooooo o o ° 000°-9 ~v
V vZt
20
& & ~ &&&AAA&& AA~A&& & & & & ~ 4 &A & A A A 4 & ~ A A A & &&AA & & & 4 ~
,A •
t
50
I
I
I
I
50
40
50
60
TEMPERATURE
X=0"21 70
80
(K)
Fig. 2. Temperature dependenceof resistance of various Lal _,PrSrxCuO4_ysamples.
D. G. Kuberkar et al. / Structural and superconducting properties of La l_ xPrSrxCuO4
The temperature dependence of the resistivity of many samples La~_xPrSrxCuO4 has been measured and is shown in fig. 2. It is clear that as the Sr-concentration increases, the metallicity of the material also increases. The Lao.sPrSro.2CuO4 sample exhibits a maximum Tc~25 K. The variation of superconducting transition temperature as a function of Stconcentration has been plotted in fig. 3 which shows that Tc increases slowly with the increase in Sr-concentration up to x = 0 . 2 above which Tc starts falling down rapidly. This behaviour is very similar to that observed in the La2_xSrxCuO4 system. In table 1 are shown the crystallographic details and the values of Tc of various samples of the system Lal_xPrSrxCuO4. Figure 4 shows AC susceptibility, as a function of temperature, of various La]_xPrSrxCuO4 samples. It is evident from the figure that both the strength of the diamagnetic signal and Tc are maximum for the sample with x=0.2. Samples with x = 0 . 0 5 and 0.30 do not exhibit any diamagnetic response down to 12 K which implies that these samples either do not superconduct or their T~ is below 12 K. A very striking feature of the present work is that the system under investigation, La~_xSrxPrCuO4, exhibits a transition from the T ' - to the T-structure. Many other systems La~ _ x S r x R f u O 4 , that have been studied for their structural and superconducting properties, however, transform from T ' - to T*-struc-
30 La l _ x P r S r x Cu 0 4
o 20
10 I 0.0
0.1
I
I
o.z
0.3
10.4
Sr c o n t e n t (X) Fig. 3. Variation of Tc as a function of Sr-content for Lal _xPrSrxCuO4_r.
Table 1 Structural and superconducting properties of Lal_~PrSrxCu04 x
Phase
Tc (K)
0.0 0.05 0.1 0.15 0.2 0.25 0.3
T' T' + T T'+T T' + T T T T
21 24 25 17 < 12
50 Lal_ x P r Sr x CuOn_y
Oo o o
40
o
o
X=0.2
o
t
o X = O . 15
o
30
v X=O.I
o
A X= 0,25
o °e.
r"
xi
•
20
" X = 0.05
o o
v v
v
I0
<
o v
I A&
0
atO •
-IC 0
I I0
&
• q7
o •
0
AU6Q • ~ VdVoVal3~UO • ~VOe~Qe~IOVOVOO
I 20
151
I 30
OOm0~V ~
• ~IOv V V V V I
I 40
50
TEMPERATURE (K) 313Hz 50mV Fig. 4. Temperature dependence of AC susceptibility for La~ _=PrSrxCuO4_~ samples.
152
D.G. Kuberkar et al. / Structural and superconducting properties of Lat_xPrSrxCu04
ture. This shows that the nature of the transition (T'--,T or T'--,T*) critically depends upon the size of the rare earth ion R. Systems in which the difference in the radii of the rare earth atoms is larger than FLa--rpr transform to T*-structure.
4. Conclusion
We have investigated structural and superconducting properties of the system La~_xSrxPrCuO4. The system transforms, for x = 0.2, to the T-structure which must be contrasted with the situation in many other systems La~_xSrxRCuO4 which transform to the T*-structure. The system exhibits superconduc-
tivity for 0.1 < x < 0 . 2 5 , Tc being the highest ( = 2 5 K) for x=0.2.
References [ 1 ] T. Takayama-Muromachi, Y. Matsui, Y. Uchida, F. Izumi, M. Onoda and K. Kato, Jpn. J. Appl. Phys. 29 ( 1989 ) L2283. [ 2 ] Y. Tokura, A. Fujimori, H. Matsubara, H. Watabe, H. Takagi, S. Uchida, M. Sakai, H. Ikada, S. Okuda and S. Tanaka, Phys. Rev. B 39 (1989) 9704. [ 3 ] J.B. Goodenough and A. Manthiram, Physica C 157 ( 1989 ) 439. [4] Y.Y. Xue, P.H. Hor, R.L. Meng, Y.K. Tao, Y.Y. Sun, Z.J. Huang, L. Gao and C.W. Chu, Physica C 165 (1990) 357. [5] K.K. Singh, P. Ganguly and C.N.R. Rao, Mat. Res. Bull. 17 (1982) 493.