Poole Ch.P., Jr. Handbook of Superconductivity
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346
Chapter 8: Crystal Structures of High-T c Superconducting Cuprates
Compound Space group a (/k) b (A) c (A) T c (K) Ref.
Bo.sBal.2Sro.8YCu2.507 a
P4/mmm
3.8776 11.336 51 1
Bo.sBa1.sSro.sYo.gsCao.15Cu2.507 a
tetr. 3.8656 11.456 55 2
Co.35No.15Ba2Yo.5Cao.5Cu2.507 a
orth. 3.879 3.885 11.536 C 82 3
Co.75Sr2.1Cao.9Cu2Oy d tetr. 3.851 10.941 e 92 4
Co.55Bao.45 Sr2.5Ca.o.5Cu20 ( tetr. 3.86 10.62 105 5
Co.TSr2Cao.7Yo.3Cu2.307 a Pmmm
3.8386 3.8586 10.97 b 40 g 6
Co.47Sr2Cao.sYo.sCu2.4206.79 h
Pmmm
3.8319 3.8501 11.1144 i 226 6
So.22Bal.5 Sro.6Yo.74Cao. 16Cu2.7807 a ... 3.85 b 11.60 b 78 7
S0.22Sr2.1Yo.74Cao. 16Cu2.7807.12 Pmmm
3.8254 3.8436 11.2572 45 8
a
Nominal composition.
b Value taken from figure.
c Additional reflections indicate superstructure (2a, b, 2c).
d prepared at 6 GPa; nominal composition.
e
Additional reflections indicate superstructure (4a, a, 2c).
fPrepared at 5 GPa; nominal composition.
g From resistivity measurements (zero resistivity); value taken from figure.
h Carbon and oxygen content
C0.51Sr2Cao.5Y0.5Cu2.4206.92
from chemical analysis.
;Additional reflections indicate superstructure.
References: 1, Zhu
et al.
(1993); 2, Slater and Greaves (1993); 3, Maignan
et al.
(1993b); 4, Yamaura
et aL
(1994); 5, Uehara
et al.
(1994b); 6, Miyazaki
et al.
(1994); 7, Slater
et al.
(1993b); 8, Slater
et al.
(1993a).
The first identified superconducting Cu-1212 compound, Ba2YCu307_ 6
(6 = 0.1, T c = 91 K), was found to crystallize in an orthorhombic cell with
a= 3.8218, b= 3.8913, and c= 11.677A (Cava
et al.,
1987b). Structural
models were proposed by Hazen
et al.
(1987), Grant
et al.
(1987), and Beyers
et al.
(1987), who, however, chose noncentrosymmetric, tetragonal or orthor-
hombic, space groups. For the superconducting, orthorhombic modification,
space group
Pmmm
was adopted by LePage
et al.
(1987), Siegrist
et al.
(1987b), Izumi
et al.
(1987a), Beno
et al.
(1987), Beech
et al.
(1987), Greedan
et al. (1987),
and Capponi
et al. (1987).
An ordered arrangement of the oxygen
atoms in the
additional
layer, resulting in the formation of chains of comer-
sharing CuO4 squares, was proposed in the latter four articles. For the tetragonal
modification space group
P4/mmm
was reported in LePage
et al.
(1987) and
Izumi
et al.
(1987b). The orthorhombic structure exists in the range 6 = 0-0.6
(Ba2YCu3Oy, y = 6.4-7) (Fig. 8.27), the highest critical temperature, Tc = 93 K,
being observed for the oxygen content
Ba2YCu306.93
(Fig. 8.28), which
corresponds to an occupancy of 0.93 for the O site in the
additional AO'
layer
(1 (e) 0 1 0). Partial occupancy of the O position, which in space group
P4/mmm
is related to the former by symmetry (1 (b) 1 0 0), is generally reported (<0.20).
The occupancy of this site increases on decreasing the overall oxygen content,
and a transition to the tetragonal structure takes place near 6 = 0.6 (sample
quenched from 873 K), suppressing the superconductivity. It should be noted that
the orthorhombic structure may be retained (and the superconductivity preserved)
to a lower oxygen content (6 = 0.8), by removing the oxygen atoms at lower
H. Crystallographic Data Sets
347
Fig. 8.27.
11.88 , I , ) , I , I ' I ' I ' I ' i ' I '
11.82
11.76
~ 11.70
~ 11.64
~ 3.89"
s:~ 3.87
~ 3.85
..0--"
- c
0"-"
m
" b
O--
-O
-
3.83 ~
0"-'--
3.81 , ~ , ~ , ) , I , I , J.. , ~ , ~ , i_ ,
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
6 in
Ba2YCu3OT.,~
Cell parameters vs 6 for Ba2YCu307_ 6 (Jorgensen
et al.,
1990).
Fig. 8.28.
6O
~ 40
100
' t ' i , t , l ' i ' i , i ' ~ , i '
80 -
O
20
0 , 1 , 1 J I , 1 , I , I , I , b '
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
(5 in
Ba2YCu307.,5
Superconducting transition temperature vs 6 for Ba2YCu307_ 6 (Jorgensen
et al.,
1990).
348
Chapter 8: Crystal Structures of High-T~ Superconducting Cuprates
temperatures (633-793 K) by a Zr-gettered annealing technique (Cava
et aL,
1987a). For the orthorhombic, as well as for the tetragonal structure, partial
vacancies on the Cu site in the
additional
layer (occupancy >0.90) were reported
to have a negative effect on the superconducting transition temperature (Collin
et
aL,
1988; Inoue
et aL,
1987). Several refinements of the orthorhombic structure
were carried out considering split sites in the
additional
layer (e.g., Cu in
2(i) 0.045 0 0 (Raudsepp
et aL,
1987) or O in 2(k) 0.0356 89 0 (Francois
et al.,
1988). The cell parameters and the oxygen content of Ba2YCu307_ 6 vs the
temperature are shown in Figs. 8.29 and 8.30, respectively.
Under certain preparation conditions, a superstructure with a doubling of
the a-parameter, usually referred to as ortho II, was observed for 6 -- 0.35-0.60
(Ba2YCu3Oy, y = 6.65-6.40; Chaillout
et al.,
1987; Schwarz
et aL,
1993). It
results from an ordering of the oxygen vacancies in the
additional
layer; however,
the correlation length is relatively short (e.g., 10.2a, 45b, 1.66c; Schleger
et aL,
1995b). A structural refinement in a 2-fold supercell, space group
Pmmm,
was
carried out by Simon
et aL
(1993) and Grybos
et aL
(1995). The structure is
characterized by an ordered arrangement of CuO and Cu chains, and the cation
sites in the
bridging, separating,
and
conducting
layers, as well as the O site in
the
bridging
layers, are displaced from the ideal positions (Burlet
et al.,
1992).
The formation of the superstructure is generally associated with a T c plateau at
about 60 K (Cava
et al.,
1987a). For a higher oxygen content (6 ~ 0.3) a different
superstructure, referred to as ortho III, with a tripling of the a-parameter (two
CuO chains alternating with one Cu chain) and an even shorter correlation length
than ortho II, was observed (Schleger
et aL,
1995a; Plakhty
et aL,
1995).
Fig. 8.29.
12.oo~_ _ . .
11.94 _ 'i '[Jori7a]
' "" ' ' 'j Zt
11.8211.88 _ 0 [Fra88] J .~
11.76 - ~ r 1
~"~'
11.70
~ 11.64
3.92 b
3.90
-
~"
3.88
(~X~] ~:510-'''~
3.86
3.84
3.82 s......,..,.,.-,-r'r'a~" ~
3.80 (~' I , I , I , t ,
0 200 400 600 800 1000 1200
Temperature (K)
Cell parameters vs temperature for
Ba2YCu307_ 6
(Jorgensen
et al.,
1987a; Francois
et al.,
1988).
H. Crystallographic Data Sets 349
Fig. 8.30.
Oh 7.0 X:xK
6.8-
6.6-
m 6.4
..~
6.2
o 0.8
-
0.6.
o 0.4
o 0.2-
9 - 0.0-
ct3
9 [Jor87a]
O [Fra88]
I ' I--' ' I ' I" '
Oin 0%0
t
Oin 89
. ~ a~.L~
I j I i I
400 600 8OO
Temperature (K)
I J I ~ I J
0 200 1000 1200
Occupancy of the O sites in the
additional
layer and oxygen content per formula unit vs
temperature for BazYCu3Oy (Jorgensen
et al.,
1987a; Fran9ois
et al.,
1988).
Numerous examples for complete or partial substitutions on all cation sites
have been tested (e.g., rare-earth elements or Ca for Y, Sr for Ba, transition
elements for Cu). Substitution of Cu by Fe, Ni, or Zn rapidly leads to a
suppression of the superconductivity. On the contrary, when Y is partly or
completely substituted by a rare-earth element, T c remains approximately the
same. Note that superconductivity for Ba2PrCu3Oy was reported relatively
recently (T c up to 90K; Blackstead
et al.,
1995; Zou
et al.,
1997).
Ba2_xRl+xCu3Oy compounds with R = La, Nd, Sm, Eu, and Gd show consider-
able homogeneity ranges with respect to the partial substitution of Ba by these
elements (Segre
et al.,
1987; Zhang
et al.,
1987), the solubility limit decreasing
with increasing atomic number of R. In the fully oxygenated compounds, a
transformation from the basic orthorhombic to the tetragonal structure, accom-
panied by a decrease of the critical temperature, is observed on increasing x (Figs.
8.31 and 8.32). BaSrRCu3OT_ 6 compounds with 6 = 0-0.07, prepared at 0.6-
0.8 GPa, crystallize with either the tetragonal (R = La, Pr, Nd, Sm, Eu, Gd, or
Dy) or the orthorhombic (R = Gd, Dy, Y, Ho, Er, or Tm) structure. The only Ba-
free superconducting compound known so far, Sr2YCu3Oy, was prepared at
7 GPa (Okai, 1990).
A superconducting T1-1212 compound (T c = 88 K) was first reported for
the composition
(T10.75Bi0.25)l.33Srl.33Cal.33Cu206.67+6 ,
and a structural model
was proposed in space group
P4/mmm
(a = 3.800, c = 12.072 A; Haldar
et al.,
1988). For Tll.169Ba2Ca0.831Cu206.747 the occupancy of the O site in the
additional
layers was refined to 0.747 and part of the thallium and barium
atoms were found to be displaced towards the oxygen vacancies (Morosin
et al.,
350 Chapter 8: Crystal Structures of High-T~ Superconducting Cuprates
Fig. 8.31.
11.82 , i , I , i , i , i ' i , i ...... ,
11.76
~, 11.70
~ 11.64
~ 3.91 (
~ 3.89
L) 3.87
3.85
- C
"----.o.
- )
" b
0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40
x in Ba2.xNdl+xCU307+ 8
Cell parameters vs x for
Ba2_xNdl+xCu307+ 6 (6 =
0 for 0 < x < 0.2) (Takita
et al.,
1988).
Fig. 8.32.
100
/ ' I ' t ' I ' I ' I ' i ' i '
1
o
80
60
~,,~' 40 ~ -
0 , I I [ J I I I I I , I I 1 J
0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40
x in Ba2.xNdl+xCU3OT+,~
Superconducting transition temperature (zero resistivity) vs x for
Ba2_xNdl+xCu307+6 (6 --
0
for 0 < x < 0.2) (Takita
et aL,
1988).
H. Crystallographic Data Sets 351
1988). The cell parameters and the critical temperature ofT1Ba2_xLaxCaCu20 7 vs
the La content are presented in Figs. 8.33 and 8.34, respectively. For the
refinement on Tlo.sPbo.sSr2CaCu207, the oxygen atoms in the T10 layer were
displaced along the diagonals of the square face of the tetragonal cell
(4(/') 0.42 0.42 0) (Martin
et aL,
1989b). A similar structure was reported for
(T1,Bi)-1212 by Led6sert
et al.
(1994), whereas in Parise
et al.
(1989a) the same
atoms were displaced along the short translation vectors (4(n) 0.408 1 0). In the
latter refinement, the T1 site was also split. For
Tlo.464Pbo.5ooSr2CaCu206.963 both
the thallium and the oxygen atoms in the
additional
layer were found to be moved
from the ideal positions and partial vacancies were detected on the T1 site
(occupancy 0.964) (Ogborne and Weller, 1994a). In all the refinements discussed
earlier, the displacements of the atoms in the T10 layer result in tetrahedral
coordination of the thallium atoms.
A Pb-based 1212 compound was first reported for the composition
Pbo.yo5Sr2Yo.73Cao.27Cu2.2950 7
(Lee
et al.,
1989). A structural refinement
in space group
P4/mmm
(a = 3.8207, c = 11.826A) considered two partly
occupied cation sites in the
additional
layer, one occupied by the lead
and the other by the copper atoms (Pb in l(a)0 0 0 and Cu in 4(/)0.221 0 0,
occupancy 0.705 and 0.074) and splitting of the O site in the same layer
(4(n) 0.324 1 0). Superconductivity (T c -25K) was detected for reduced
Pbo.65SrzYo.yCao.3Cu2.3507.o5
(Maeda
et al.,
1991a). The extra oxygen atoms
in nonsuperconducting
Pbo.65Sr2Yo.yCao.3Cu2.3507.11 were
found to be located in
the
additional
layer (2(f) 0 1 0).
Fig. 8.33.
o<
E
12.79
12.76
12.73
12.70
12.67
12.64
12.61
3.86
3.85
3.84
3.83
0.0
" ""1' ' i ' I ' I ' I ~" I' ' t" ' I ' ! '
-
- -
.
a
, I , I , I J I , I J I , I ,
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
x in T1Baz.xLaxCaCu207
Cell parameters vs La content for T1Ba2_xLaxCaCu207 (Badri and Varadaraju, 1995).
352
Chapter 8:
Fig. 8.34.
Crystal Structures of High-T c Superconducting Cuprates
120
100
80
60
40
20
0
0.0
' I ' ! ' I '" .... I i" I ' I ' I ' ! "' I '
o
/4
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 .0
X in T1Ba2.xLaCaCu207
Superconducting transition temperature (zero resistivity) vs La content
T1Ba2_xLaxCaCu207 (Badri and Varadaraju, 1995).
for
A superconducting Ga-1212 compound (T c = 35 K) was first reported for
the nominal composition GaSr2Ero.6Cao.aCu207 (Cava
et aL,
1991). The crystal
structure, like that of Ga-1201, is orthorhombic because of the arrangement of
GaO4 tetrahedra in chains.
Nonsuperconducting Hg-1212 compounds were reported for the composi-
tion HgBa2RCu207 (R = La, Nd, Eu, Gd, Dy, and Y; Putilin
et al.,
1991). They
crystallize with a tetragonal structure
(P4/mmm,
a = 3.8905, c = 12.546 A for
HgBa2Eu0.76Cao.24Cu207). After the discovery of superconductivity in the Hg-
Ba-Ca-Cu-O system (Schilling
et al.,
1993), the structures of Hg-based
compounds with T c up to 128 K were refined by many research groups, who
reported similar results. In particular, it was noted that a partly occupied O site is
generally present in the
additional
layer, but its occupancy does not exceed 0.40.
The critical temperature depends on the oxygen content, the maximum value
being reached for 6 = 0.24-0.27 (Radaelli
et aL,
1993b; Loureiro
et al.,
1993).
The first synthesis of a carbon-containing Cu-1212 compound was reported
by Karen and Kjekshus (1991). A structural refinement carried out in space group
Pmmm
(a = 3.8278, b = 3.8506, c = 11.1854 A) showed that carbon had partly
substituted for copper in the
additional
layers, yielding the overall composition
Co.4Sr2.14Yo.86Cu2.60 7
(Miyazaki
et al.,
1992c). Superstructures with ordered
arrangements of rows of CO3 triangles and chains of corner-linked CuO4 squares
(2a, b, 2c and 3a, b, 2c) were proposed by Miyazaki
et al.
(1992c) and Ohnishi
et al.
(1993). A critical temperature of 63 K was reported for the composition
Co.65r2.o5Yo.475Cao.475Cu2.4Oy , for which a 4-fold superstructure with a B-
H. Crystallographic
Data
Sets
353
centered orthorhombic cell was suggested (Akimitsu
et al.,
1992). Two different
superstructures in space group
Bm2m
were refined for (Co.25Cuo.y5)Sr2YCu20 7
and (Co.sCuo.s)BazYCu207, respectively (a = 15.311, b = 3.851, c = 22.371 A
and a = 7.7704, b = 3.8876, c = 22.9812 A; Domeng6s
et al.,
1993, 1994), the
latter being identical to the one mentioned earlier. More superstructures with
similar ordered arrangements of carbon and copper atoms in the
additional
layer
can be derived from the average structure. One short cell parameter (b) remains
the same while the other is multiplied by a factor that depends on the C/Cu ratio.
1222
CUl (Bao.63Ndo.37)2( N do.67Ceo.33 )2Cu208.91
AB2C2D209,
ti32, (139)
I4/mmm-ge4dca
-0 2 D--C,-02-,
C-DO2-OB-A O"-OB-
Bal.z66Ndz.og4Ceo.65Cu308.912, T c =
37 K, a PN, RT,
R 8 = 0.0385 (Izumi
et al.,
1989a)
(139)
I4/mmm,
a = 3.8747, c = 28.599 A, Z = 2 Fig. 15
Atom WP PS x
Occ.
Cu(1 ) 8(h) m. 2m 0.0527
1
Ba b 4(e)
4mm
Cu(2) 4(e)
4ram 0
1
Nd r 4(e)
4mm
O(1) 16(/) m.. 0.060
O(2) 16(m) . .m 0.054
0(3) 8(g)
2mm . 0
0(4) 4(d) 4m2 0
0.0527
1
_
2
0
1
0.440
0.054
1
_
2
1
0
0.0756
0.1418
0.2044
0
0.0639
0.1475
1
_
4
0.25
0.114
0.25
a Value taken from figure.
bBa
= Bao.633Ndo.367.
c Nd
= Ndo.675Ceo.325.
(continued)
354
Chapter 8: Crystal Structures of High-T c Superconducting Cuprates
Compound
a (A) c (A) T c (K) Ref.
TiSr2Ndl.5Ceo.5Cu2Oya
TaSr2Ndl.5Ceo.5Cu2Oya
NbSr2Prl.5Ceo.5Cu2Olo
NbS1"2Ndl.5Ceo.5Cu2010_6 a
NbSr2 Sm 1.5Ceo.5Cu2010
NbSr2 Eu 1 .sCeo.sCu2010
NbSr2Gdl.sCeo.5CUEOy a
Ba1.266 Nd2.084Ce0.65Cu308.912
Bal.34Eu2Ceo.66Cu308.54
Bao.67Sro.67Lao.67Gdl.33Ceo.67Cu309. 415 a
Ba 1.33 Lao.67Gd 1.33 C eo. 67 Cu3010-6 a
Ba 1.33LaGdCeo.67Cu3010-6 a
Sr1.7Sm1.6Ceo.7Cu3 O8+di a
Srl.8EUl.6Ceo.6Cu308.6
Alo.25Sr1.33Eu2.17Ceo.5Cu2.7508+6 a
Feo.25 Sr1.33Eu2.17Ceo.5Cu2.7508+6 a
Coo.25Sr1.33Eu2.17Ceo.sCu2.7508+6
a
RuSr2Gdl.5Ceo.5Cu2Olo a
Co.35Sr2Yl.a6Ceo.54Cu2.6509
3.873 28.36 n.s. 1
3.881 28.93 n.s. 1
3.8870 28.752 n.s. 2
3.885 28.864 28 3
3.8709 28.791 28 2
3.8687 28.774 28 2
3.8669 28.742 13 b 4
3.8747 28.599 37 c 5
3.85044 28.4598 33 6
3.842 28.349 38 7
3.858 28.489 25 7
3.833 28.298 40 7
3.8562 28.18 30 8
3.84048 28.0748 36 8
3.846 c 27.95 C 18 9
3.836 r 28.20 c 26 9
3.839 c 28.22 ~ 36 9
3.836 28.58 42 a 10
e 18 11
a
Nominal composition.
b From resistivity measurements (zero resistivity).
r Value taken from figure.
d Tr
given for RuSr2Gdl.aCeo.6Cu2Olo (value taken from figure).
e Space group
Immm,
a = 3.8272, b = 3.8313, and c = 27.7077A.
References: 1, Li
et al.
(1991); 2, Goodwin
et al.
(1992); 3, Cava
et al.
(1992); 4, Wang
et al.
(1993);
5, Izumi
et al.
(1989a); 6, Sawa
et al.
(1989a); 7, Wada
et al.
(1990a); 8, Kopnin
et al.
(1994); 9,
Ichinose
et al.
(1992); 10, Bauernfeind
et al.
(1995); 11, Miyazaki
et al.
(1992b).
H. Crystallographic Data Sets 355
1222
AB2C2D209, ti32, (139) I4/mmm-ge4dba
-02D-C.-O2-.
C-DO2-OB-A O-OB-
T1BazEul.sCeo.sCu209, T c -- 40 K, PX, RT, R B -- 0.0944
(Liu
et al., 1992a)
(139)
I4/mmm, a = 3.8782, c = 30.423 A, Z = 2 Fig. 16
TllBa2(Euo.v5Ceo.25)2Cu209
Atom WP PS x z Occ.
T1 8(i)
m2m. 0.082
1
Ba 4(e) 4mm
Cu 4(e) 4ram 0
1
Eu a 4(e) 4mm
1
O(1) 2(b) 4/mmm
0(2) 4(e) 4mm 0
0(3) 8(g) 2mm . 0
0(4) 4(d) 4m2 0
0
1
2
0
1
1
2
0
1
2
1
2
0
0.0872
0.1520
0.2087
0
0.0831
0.1554
1
4
0.25
a Eu = Euo.75Ceo.25.
Compound
a (A)
c (A)
T~ (K) Ref.
T1Ba2Eul.sCeo.sCu209
Tlo.7Hgo.3 SrzPrzCu209
T1Sr2Ndl.sCeo.sCu209 a
Tlo.sTio.zSrzNdl.sCeo.sCuzO9
a
Tlo.sNbo.2Sr2Ndl.sCeo.sCu209 a
Tlo.7Pbo.3Sr2Ndl.5Ceo.sCu209 a
Tlo.sPbo.5SrzEUl.gCeo.zCuzO9 a
Tlo.sPbo.5 SrzGdl.6Ceo.4Cu209
Gao.sSrl.sEu2Ceo.sCu2.509
a
Gao.8SrzY
1.4Ceo.6Cu2.209_6 a
Pbo.5Srl.75EUl.75Ceo.5Cu2.509
3.8782
3.8642
3.851
3.847
3.852
3.853
3.91
3.8429
3.840
3.812
3.83795
30.423 40 1
29.568 n.s. 2
29.64 30 3
29.43 27 b 4
29.45 20 b 4
29.61 20 b 5
29.98 40 6
29.5097 46 7
28.14 28 8
28.16 14 9
29.0116 25 10, 11
(continued)