- Email: [email protected]
New oxide superconductors
PhysicaC 153-155 (1988) 608 612 North-Holland, Amsterdam
NEW
OXIDE SUPERCONDUCTORS
M. A. Subramanian, C. C. Torardi, J. Gopalakrishnan, J. C. Calabrese, K. J. Morrissey, T. R. Askew, R. B. Flippen, U. Chowdhry and A. W. Sleight Central Research and Development Department, E. I. du Pont de Nemours Company, Experimental Station, Wilmington, Delaware 19898, USA.
and
and J. J. Lin and S. J. Poon Department
of Physics,
University of Virginia,
Charlottesville,
VA 22906,
USA.
Crystals of the new high temperature superconductor Bi2Sr3_xCaxCu208+y have been grown and studied. Single crystal x-ray diffraction data were used to determine a pseudo tetragonal structure based on an A-centered orthorhombic cell with a = 5.399 ~, b = 5.414 ~ and c = 30.904 ~. The structure contains the copper-oxygen sheets as in La2CuO 4 and YBa2Cu307, but the copper-oxygen chains present in YBa~Cu307 do not occur in Bi2Sr3_xCaxCu208+ ~. Electrical m e a s u r e m e n t s on our single crystals show a resistivity drop a% about 116 K and apparent zero resistivity at 91 K. We find superconductivity at 120 K in the T [ / C a / B a / C u / O system. Also, we have for the first time prepared phases of the type La~-xNaxCuO 4. These materials are superconducting with Tc's as high as 40 K, and they have some unusual magnetic behavior starting at about 10 K.
i. INTRODUCTION The first d i s c o v e r y of high temperature s u p e r c o n d u c t i v i t y in copper oxide based systems was for the La2_xAxCuO4 system where A is Ba, Sr or Ca (1,2). We have now found that A may also be Na or K, and the properties of these materials are p r e s e n t e d in this paper. Very recently Maeda et al. (3) reported high temperature s u p e r c o n d u c t i v i t y in the B i / S r / C a / C u / O system, and one might then speculate that this s u p e r c o n d u c t i v i t y is in some way related to the s u p e r c o n d u c t i v i t y in the B a ( P b , B i ) O 3 system (4). Even more recently Sheng and Herman (5) have reported s u p e r c o n d u c t i v i t y in the T Z / C a / B a / C u / O system for phases which appear s t r u c t u r a l l y related to Bi2Sr3-xCaxCu~Os+y. 2. BISMUTH C O N T A I N I N G S U P E R C O N D U C T O R S A report of our work in this system has been p u b l i s h e d (6) where certain details may be found. However, we now have more results regarding the structure and p r o p e r t i e s of the hightemperature s u p e r c o n d u c t o r which we formulate as Bi2Srs_xCaxCu2Os+y. 0921-4534/88/$03.50 © Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)
Our structural refinement is based on single crystal x-ray d i f f r a c t i o n data using the o r t h o r h o m b i c Amaa s~ace group with a = 5.399 ~, b = 5.414 A and c = 30.904 ~. Our R value is 0.055, and the refined p a r a m e t e r s are given in Table I. As can be seen in Figure i, there are c o p p e r - o x y g e n sheets where copper is in e s s e n t i a l l y square planar coordination to oxygen (Cu-O = 1.91 ~), but there is a fifth oxygen at about 2.45 ~. A l t h o u g h the cations between adjacent Cu-O sheets are p r i m a r i l y Ca 2+, there are also some cations with higher atomic number. Based on our chemical analysis, we believe that some Sr has s u b s t i t u t e d for Ca. Our structural refinement based on the 5.4 X 5.4 X 31 ~ cell gives a well defined s t r u c t u r e for St, Ca, Cu and the oxygen bound to Cu. However, the structure is not well d e f i n e d with regard to Bi and the oxygen atoms bound to Bi. This lack of d e f i n i t i o n is directly related to an incommensurate s u p e r s t r u c t u r e along the a axis. We can consider the structure of B i 2 S r 2 C a C u 2 0 s (idealized formula) as closely related to that of YBa2Cu307. The S r - C u O 2 - C a - C u O 2 - S r section of
M.A. Subramanian et al.
Bi2Sr2CaCu~O 8 is essentially the same as the Ba-CuO2-Y-CuO2-Ba section of YBa2Cu307. However, for Bi2Sr2CaCu208 these sections are separated by double Bi-O layers whereas for YBa2Cu307 these sections are separated by the Cu-O chains. The Cu-O chains which seemed so important for the properties of YBa2Cu307 are not present in Bi2Sr2CaCu208 but Bi-O chains are possible. Electrical measurements on a single crystal (Fig. 2) show apparent zero resistivity at 91 K. Preliminary critical current measurements by the Bean method show about 105 amp/cm 2 at 7 K. Flux exclusion (Fig. 3) indicates onset behavior close to 120 K. 3. SODIUM SUBSTITUTION INTO La2CuO 4 The La 2 series was • _ - - xA~-Cu04__ j prepared in sealed gold tubes uslng appropriate quantities of La203, CuO and either Na202 or K0~. Calcination was carried out at 900°C under both 1 and 3000 arm pressure. The higher pressure synthesis gives lower oxygen deficiency (Table 2) and better superconducting properties. As the alkali content increases, the room temperature orthorhombic symmetry of La2CuO 4 changes to tetragonal. Also, with increasing x the a cell edge decreases (Table 3) and thus the Cu-O distance decreases from 1.901 ~ to 1.888 ~ for Lal.7Nao.$Cu04. The electrical resistivity behavior for La 2 xNaxCu04 _ samples prepared at hlgh pressure is shown in Figure 4. For low sodium content, the materials are semiconducting and not superconducting. With increasing x, metallic properties and superconductivity as high as about 40 K develops. Magnetic susceptibility data for three La2_xNaxCuO4_v samples (Figure 5) clearly establish bulk superconductivity. However, unusual magnetic behavior is found below i0 K.
/
609
New oxide superconductors
(5) (6)
Z. Z. Sheng and A. M. Herman, Phys. Rev. Lett., in press. M. A. Subramanian, C. C. Torardi, J. C. Calabrese, J. Gopalakrishnan, K. J. Morrissey, T. R. Askew, R. B. Flippen, U. Chowdhry and A. W. Sleight, Science 239 (1988) 1015.
o
o
Oo
,o %1, Oo
d •
Ii
- -
_ C_~.
Ca(Sr)
C~
Sr
00
o, , ©
O
- -
Bi
- -
Bi
- -
Sr
- -
Cu
- -
Cu
- -
Sr
©
Q
Ca(Sr)
..
jg
w
jg
I,
Bi
o kLOo--- Oo o
REFERENCES FIGURE 1 (i) (2) (3) (4)
J. G. Bednorz and K. Muller, Z. Phys. B64 (1986) 189. S. Uchida, H. Takagi, K. Kitazawa and S. Tanaka, Jap. J. Appl. Phys. 26 (1987) LI. M. Maeda, Y. Tanaka, M. Fukutomi and T. Asano, Jap. J. Appl. Phys. Lett., in press. A. W. Sleight, J. L. Gillson and P. E. Bierstedt, Solid State Commun. 17 (1975) 27.
Structure of Bi2Sr3_xCaxCu2Os+y showing the CuO 2 layers. Metal atoms are shaded and only Cu-O bonds are shown. Oxygen atoms for the Bi layers are idealized.
610
M.A. Subramanian et al. / N e w oxide superconductors
TABLE 1 Positional a and Thermal b Parameters Bi2Sr3-xCaxCu208+y.
for the Atoms of
Atom
x
y
z
B (~2)
Bi(1) St(1) Cu(1) Ca/St 0(i) 0(2) 0(3)
0.4492(10) 0.00 0.50 0.00 0.75 0.25 0.4347(90)
0.2277(4) 0.2532(9) 0.2506(10) 0.25 0.00 0.50 0.2600(88)
0.0522(1) 0.1408(2) 0.1971(2) 0.25 0.1969(12) 0.2028(14) 0.1176(13)
2.7(1)' 3.1(2)' 2.5(2)' 2.3(3)' 1.8(8)' 2.6(10) 3.4(10)
aBi(1) and 0(3) statistically distributed bewteen two closely spaced sites. bMetal atoms refined with anisotropic thermal parameters.
TABLE 2 Copper Nominal La I Lal La I La I
•
(III) Concentration
composition
8Nao 2Cu04_~ 8Nao.2CuO4-y 7Nao 3Cu04__ 7Nao.3CuO4_y •
Pressure 1 3 1 3
3
in La2_xNaxCuO4_y
Samples
CuIII/Total
atm kbar atm kbar
Cu
0.15 0.19 0.18 0.21
TABLE 3 Cell Dimensions
for Some La2_xA~Cu04
Nominal Composition La2CuO 4 Lal.gNao.iCuO 4 Lal.8Nao.2CuO 4 Lal.7Nao.3CuO4 Lal.sNao.sCuO 4 Lal.8Ko.2Cu04 *La2CuO 4 is actually orthorhombic;
Oxides at Room Temperature
a (~)
c (~)
3.802* 3.783 3.778 3.775 3.775 3.783
13.167 13.179 13.176 13.170 13.156 13.192
this
'a' value
is (a+b)/252.
M.A. Subramanian et al. / New oxide superconductors
611
30
120 108
•
(a) SINGLE CRYSTAL
•
(b) POLYCRYSTALLINE
27 it) ~
"
96
24
84
21
72
18
so
15
m o E E
E to
48
n-
36 24
12 0 60
80
100
120
140
160
180
200
220
240
260
280
300
T (K)
FIGURE Resistivity
curves
for
2
Bi2Sr3_xCaxCu208+y
superconductor•
1.5
;IGNAL MAGNIFIED BY30X
D
/ O
80
! ~ .4°--
"~.
\
\ /
JJ TEMPERATURE (K)
FIGURE
3
Magnetic flux exclusion of a few randomly oriented single crystals B i 2 S r 3 _ x C a x C u 2 O s + y s u p e r c o n d u c t o r m e a s u r e d by an AC susceptometer.
of
612
M.A. Subramanian et al.
/ N e w oxide superconductors 5.0
C.O
14
4.5" A
4.0"
5.0
HDc=O
3.5"
3.0-
4,0
X
HDC=20G/
2.5" 5 3.0
J
~
2.0-
~
1.5-
15
10
1.O" 0
/
0.5"
1.0
0.O -0.5'
.0
-I
.0
-1.5
~ I I I
I I00
I I I I
I 200
I I I I
I-I.0 300
T(K)
FIGURE 4
R e s i s t i v i t y curves for L a ~ _ x N a x C u O 4 _ samples. (a) x = 0.i, (b~ 0.3 and (6) 0.5. The room temperature specific resistivities of these samples are ii.i, 2.8 and 2.2 mohm-cm, respectively.
-2.0
S I%
20
~o
I
41
I
50
T (K)
FIGURE
5
Magnetlc s u s c e p t i b i l i t y curves for L a 2 _ x N a x C u O 4 _ v samples. (a) x = 0.5 prepared at atmospheric conditions, (b) x = 0.3 p r e p a r e d under 3 kbar, and (c) x = 0.5 p r e p a r e d under 3 kbar. Inset shows m a g n e t i c s u s c e p t i b i l i t y data at different fields for x = 0.5 sample prepared under 3 kbar.
NEW
OXIDE SUPERCONDUCTORS
M. A. Subramanian, C. C. Torardi, J. Gopalakrishnan, J. C. Calabrese, K. J. Morrissey, T. R. Askew, R. B. Flippen, U. Chowdhry and A. W. Sleight Central Research and Development Department, E. I. du Pont de Nemours Company, Experimental Station, Wilmington, Delaware 19898, USA.
and
and J. J. Lin and S. J. Poon Department
of Physics,
University of Virginia,
Charlottesville,
VA 22906,
USA.
Crystals of the new high temperature superconductor Bi2Sr3_xCaxCu208+y have been grown and studied. Single crystal x-ray diffraction data were used to determine a pseudo tetragonal structure based on an A-centered orthorhombic cell with a = 5.399 ~, b = 5.414 ~ and c = 30.904 ~. The structure contains the copper-oxygen sheets as in La2CuO 4 and YBa2Cu307, but the copper-oxygen chains present in YBa~Cu307 do not occur in Bi2Sr3_xCaxCu208+ ~. Electrical m e a s u r e m e n t s on our single crystals show a resistivity drop a% about 116 K and apparent zero resistivity at 91 K. We find superconductivity at 120 K in the T [ / C a / B a / C u / O system. Also, we have for the first time prepared phases of the type La~-xNaxCuO 4. These materials are superconducting with Tc's as high as 40 K, and they have some unusual magnetic behavior starting at about 10 K.
i. INTRODUCTION The first d i s c o v e r y of high temperature s u p e r c o n d u c t i v i t y in copper oxide based systems was for the La2_xAxCuO4 system where A is Ba, Sr or Ca (1,2). We have now found that A may also be Na or K, and the properties of these materials are p r e s e n t e d in this paper. Very recently Maeda et al. (3) reported high temperature s u p e r c o n d u c t i v i t y in the B i / S r / C a / C u / O system, and one might then speculate that this s u p e r c o n d u c t i v i t y is in some way related to the s u p e r c o n d u c t i v i t y in the B a ( P b , B i ) O 3 system (4). Even more recently Sheng and Herman (5) have reported s u p e r c o n d u c t i v i t y in the T Z / C a / B a / C u / O system for phases which appear s t r u c t u r a l l y related to Bi2Sr3-xCaxCu~Os+y. 2. BISMUTH C O N T A I N I N G S U P E R C O N D U C T O R S A report of our work in this system has been p u b l i s h e d (6) where certain details may be found. However, we now have more results regarding the structure and p r o p e r t i e s of the hightemperature s u p e r c o n d u c t o r which we formulate as Bi2Srs_xCaxCu2Os+y. 0921-4534/88/$03.50 © Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)
Our structural refinement is based on single crystal x-ray d i f f r a c t i o n data using the o r t h o r h o m b i c Amaa s~ace group with a = 5.399 ~, b = 5.414 A and c = 30.904 ~. Our R value is 0.055, and the refined p a r a m e t e r s are given in Table I. As can be seen in Figure i, there are c o p p e r - o x y g e n sheets where copper is in e s s e n t i a l l y square planar coordination to oxygen (Cu-O = 1.91 ~), but there is a fifth oxygen at about 2.45 ~. A l t h o u g h the cations between adjacent Cu-O sheets are p r i m a r i l y Ca 2+, there are also some cations with higher atomic number. Based on our chemical analysis, we believe that some Sr has s u b s t i t u t e d for Ca. Our structural refinement based on the 5.4 X 5.4 X 31 ~ cell gives a well defined s t r u c t u r e for St, Ca, Cu and the oxygen bound to Cu. However, the structure is not well d e f i n e d with regard to Bi and the oxygen atoms bound to Bi. This lack of d e f i n i t i o n is directly related to an incommensurate s u p e r s t r u c t u r e along the a axis. We can consider the structure of B i 2 S r 2 C a C u 2 0 s (idealized formula) as closely related to that of YBa2Cu307. The S r - C u O 2 - C a - C u O 2 - S r section of
M.A. Subramanian et al.
Bi2Sr2CaCu~O 8 is essentially the same as the Ba-CuO2-Y-CuO2-Ba section of YBa2Cu307. However, for Bi2Sr2CaCu208 these sections are separated by double Bi-O layers whereas for YBa2Cu307 these sections are separated by the Cu-O chains. The Cu-O chains which seemed so important for the properties of YBa2Cu307 are not present in Bi2Sr2CaCu208 but Bi-O chains are possible. Electrical measurements on a single crystal (Fig. 2) show apparent zero resistivity at 91 K. Preliminary critical current measurements by the Bean method show about 105 amp/cm 2 at 7 K. Flux exclusion (Fig. 3) indicates onset behavior close to 120 K. 3. SODIUM SUBSTITUTION INTO La2CuO 4 The La 2 series was • _ - - xA~-Cu04__ j prepared in sealed gold tubes uslng appropriate quantities of La203, CuO and either Na202 or K0~. Calcination was carried out at 900°C under both 1 and 3000 arm pressure. The higher pressure synthesis gives lower oxygen deficiency (Table 2) and better superconducting properties. As the alkali content increases, the room temperature orthorhombic symmetry of La2CuO 4 changes to tetragonal. Also, with increasing x the a cell edge decreases (Table 3) and thus the Cu-O distance decreases from 1.901 ~ to 1.888 ~ for Lal.7Nao.$Cu04. The electrical resistivity behavior for La 2 xNaxCu04 _ samples prepared at hlgh pressure is shown in Figure 4. For low sodium content, the materials are semiconducting and not superconducting. With increasing x, metallic properties and superconductivity as high as about 40 K develops. Magnetic susceptibility data for three La2_xNaxCuO4_v samples (Figure 5) clearly establish bulk superconductivity. However, unusual magnetic behavior is found below i0 K.
/
609
New oxide superconductors
(5) (6)
Z. Z. Sheng and A. M. Herman, Phys. Rev. Lett., in press. M. A. Subramanian, C. C. Torardi, J. C. Calabrese, J. Gopalakrishnan, K. J. Morrissey, T. R. Askew, R. B. Flippen, U. Chowdhry and A. W. Sleight, Science 239 (1988) 1015.
o
o
Oo
,o %1, Oo
d •
Ii
- -
_ C_~.
Ca(Sr)
C~
Sr
00
o, , ©
O
- -
Bi
- -
Bi
- -
Sr
- -
Cu
- -
Cu
- -
Sr
©
Q
Ca(Sr)
..
jg
w
jg
I,
Bi
o kLOo--- Oo o
REFERENCES FIGURE 1 (i) (2) (3) (4)
J. G. Bednorz and K. Muller, Z. Phys. B64 (1986) 189. S. Uchida, H. Takagi, K. Kitazawa and S. Tanaka, Jap. J. Appl. Phys. 26 (1987) LI. M. Maeda, Y. Tanaka, M. Fukutomi and T. Asano, Jap. J. Appl. Phys. Lett., in press. A. W. Sleight, J. L. Gillson and P. E. Bierstedt, Solid State Commun. 17 (1975) 27.
Structure of Bi2Sr3_xCaxCu2Os+y showing the CuO 2 layers. Metal atoms are shaded and only Cu-O bonds are shown. Oxygen atoms for the Bi layers are idealized.
610
M.A. Subramanian et al. / N e w oxide superconductors
TABLE 1 Positional a and Thermal b Parameters Bi2Sr3-xCaxCu208+y.
for the Atoms of
Atom
x
y
z
B (~2)
Bi(1) St(1) Cu(1) Ca/St 0(i) 0(2) 0(3)
0.4492(10) 0.00 0.50 0.00 0.75 0.25 0.4347(90)
0.2277(4) 0.2532(9) 0.2506(10) 0.25 0.00 0.50 0.2600(88)
0.0522(1) 0.1408(2) 0.1971(2) 0.25 0.1969(12) 0.2028(14) 0.1176(13)
2.7(1)' 3.1(2)' 2.5(2)' 2.3(3)' 1.8(8)' 2.6(10) 3.4(10)
aBi(1) and 0(3) statistically distributed bewteen two closely spaced sites. bMetal atoms refined with anisotropic thermal parameters.
TABLE 2 Copper Nominal La I Lal La I La I
•
(III) Concentration
composition
8Nao 2Cu04_~ 8Nao.2CuO4-y 7Nao 3Cu04__ 7Nao.3CuO4_y •
Pressure 1 3 1 3
3
in La2_xNaxCuO4_y
Samples
CuIII/Total
atm kbar atm kbar
Cu
0.15 0.19 0.18 0.21
TABLE 3 Cell Dimensions
for Some La2_xA~Cu04
Nominal Composition La2CuO 4 Lal.gNao.iCuO 4 Lal.8Nao.2CuO 4 Lal.7Nao.3CuO4 Lal.sNao.sCuO 4 Lal.8Ko.2Cu04 *La2CuO 4 is actually orthorhombic;
Oxides at Room Temperature
a (~)
c (~)
3.802* 3.783 3.778 3.775 3.775 3.783
13.167 13.179 13.176 13.170 13.156 13.192
this
'a' value
is (a+b)/252.
M.A. Subramanian et al. / New oxide superconductors
611
30
120 108
•
(a) SINGLE CRYSTAL
•
(b) POLYCRYSTALLINE
27 it) ~
"
96
24
84
21
72
18
so
15
m o E E
E to
48
n-
36 24
12 0 60
80
100
120
140
160
180
200
220
240
260
280
300
T (K)
FIGURE Resistivity
curves
for
2
Bi2Sr3_xCaxCu208+y
superconductor•
1.5
;IGNAL MAGNIFIED BY30X
D
/ O
80
! ~ .4°--
"~.
\
\ /
JJ TEMPERATURE (K)
FIGURE
3
Magnetic flux exclusion of a few randomly oriented single crystals B i 2 S r 3 _ x C a x C u 2 O s + y s u p e r c o n d u c t o r m e a s u r e d by an AC susceptometer.
of
612
M.A. Subramanian et al.
/ N e w oxide superconductors 5.0
C.O
14
4.5" A
4.0"
5.0
HDc=O
3.5"
3.0-
4,0
X
HDC=20G/
2.5" 5 3.0
J
~
2.0-
~
1.5-
15
10
1.O" 0
/
0.5"
1.0
0.O -0.5'
.0
-I
.0
-1.5
~ I I I
I I00
I I I I
I 200
I I I I
I-I.0 300
T(K)
FIGURE 4
R e s i s t i v i t y curves for L a ~ _ x N a x C u O 4 _ samples. (a) x = 0.i, (b~ 0.3 and (6) 0.5. The room temperature specific resistivities of these samples are ii.i, 2.8 and 2.2 mohm-cm, respectively.
-2.0
S I%
20
~o
I
41
I
50
T (K)
FIGURE
5
Magnetlc s u s c e p t i b i l i t y curves for L a 2 _ x N a x C u O 4 _ v samples. (a) x = 0.5 prepared at atmospheric conditions, (b) x = 0.3 p r e p a r e d under 3 kbar, and (c) x = 0.5 p r e p a r e d under 3 kbar. Inset shows m a g n e t i c s u s c e p t i b i l i t y data at different fields for x = 0.5 sample prepared under 3 kbar.