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ВІСНИК ЛЬВІВ. УН
-
ТУ

VISNYK LVIV UNIV.

Серія хім. 2003. Вип.43.
С.21
-
32

Ser. Khim. 2003. No 43. P.21
-
32


УДК 546
:
736


STRUCTURAL REFINEMENTS ON INTERMEDIATE PHASES Tl
-
1223


Tl
-
2223


O. Shcherban
1
, Th. Hopfinger
2
, R. Gladyshevskii
1
, Ph. Galez
2
, J.L. Jorda
2
1


1
Ivan Franko National University of L’viv,

Kyryla & Mefodiya Str. 6, UA
-
79005 L’viv, Ukraine


2
Université de Savoie, BP240, F
-
74942 Annecy Cedex, France



Formation of the intermediate phase Tl
4
Ba
6
Ca
6
Cu
9
O
28

was observed in the Tl
-
Ba
-
Ca
-
Cu
-
O

system
.
It
s crystal structure

was determined by the powder method
(
I
4/
mmm
,
a
=3.8463,
c
=98.45Å,
Z
=2). It can be considered as an intergrowth of Tl
-
1223 and Tl
-
2223 fragments in the ratio 2:1.
Structural models of other intermediate phases, the formation of which is a
lso possible during the
transformation from Tl
-
2223 to Tl
-
1223 by stepwise deintercalation of TlO layers, are presented.



Key words
: high
-
T
c

superconductors, Tl
-
Ba
-
Ca
-
Cu
-
O system, intergrowth structure.



TlBa
2
Ca
2
Cu
3
O
9
-
d

(unsubstituted Tl
-
1223) and (Tl,Pb
)(Sr,Ba)
2
Ca
2
Cu
3
O
9
-
d

(substituted
Tl
-
1223) are known to be promising materials for high
-
current applications due to their high
irreversibility fields. However, the transport properties in Tl
-
1223 wires and tapes are
dominated by weak links between the grain
s, resulting mainly from the grain morphology.
Large plate
-
like grains, commonly observed in Bi
-
based superconductors, cannot be produ
-
ced by conventional powder metallurgy and the size of the brick
-
wall
-
like Tl
-
1223 grains
rarely exceeds 5
-
10

μm. Fast for
mation kinetics impedes suitable grain growth and recrys
-
tallization is limited by the lack of liquid phase.

It has been observed that the pathways for
the formation of substituted and unsubstituted Tl
-
1223 phases are different: in the first case
it involv
es the Tl
-
1212 phase and in the second case the Tl
-
2223 phase [1]. The double TlO
layer compound crystallizes with more pronounced plate
-
like grains and an optimized
synthesis of unsubstituted Tl
-
1223 could lead to improved grain morphology.


In the course

of a general study on phase formation, crystal structure and super
-
conducting properties of TlBa
2
Ca
2
Cu
3
O
9
-
d
, aiming at improving the transport properties, we
report, in this article, the results of X
-
ray diffraction, AC susceptibility and scanning
electro
n microscopy measurements. They are discussed considering the formation path of
TlBa
2
Ca
2
Cu
3
O
9
-
d
, which will be described in details elsewhere.


Samples were synthesized in two steps. Tl
-
free precursors were first prepared from
mixtures of BaO
2

(95% purity)
, CaO and CuO at 950

°C for 12 hours in air. After addition
of Tl
2
O
3
, the samples were wrapped in Au foils and treated at temperatures ranging from
890 to 920

°C in sealed quartz tubes (
p
O
2

=

0.5

bar). Details of the syntheses are reported in
Table

1. Samp
le TB910 was submitted to several treatments with intermediate grindings and
Tl oxide addition before the second and fourth treatments. The final Tl content was
estimated from the weight loss.


Diffraction data were collected on a Philips PW1820 powder dif
fractometer with
Bragg
-
Brentano geometry (Ni
-
filtered Cu
K
α radiation, room temperature, 4<2

<90°, 0.03°
2


step width, 10 s step time).




© Shcherban O., Hopfinger Th., Gladyshevskii R. et al., 2003

22

O. Shcherban, Th. Hopfinger, R. Gladyshevskii et al.


Table 1

Thermal treatments

Sample

Tl content nominal

Tl conten
t final

Thermal treatment

TB890

1.2

0.97

890°C, 12

h

TB900

1.2

0.95

900
°
С, 12 h
=

㤱9
=
3.0
=
1.9
=
㠰8
°
С, 10 h in air
=
3.0
=
1.6
=
㠷8
°
С, 15 min
=
†=
+=800
°
С, 12 h in air
=
1.6
=
0.95
=
㤱9
°
С, 12 h
=
1.05
=
0.9
=
㤱9
°
С, 3 h
=

㤲9
=
1.O
=
0.8T
=
㤲9
°
С, 12 h
=


The crystal stru
ctures were refined by the Rietveld method using the DBWS
-
9807
program [2]. The samples were found to contain Tl
-
1223 as major phase. Small amounts of
BaCuO
2

and Ca
2
CuO
3

were detected. The occurrence of broad peaks at angles lower than
the first Tl
-
1223 pe
ak in the diffraction patterns indicated that Tl
-
2223 and one or several
intergrowth structures, combinations of Tl
-
1223 and Tl
-
2223, were formed, as mentioned in
earlier works [3,4].


Starting models for the structure refinements of Tl
-
1223 and Tl
-
2223 we
re taken
from [5]. Models for possible intergrowth structures were built of Tl
-
1223 and Tl
-
2223
stacking units, consisting of a BaO
-
CuO
2
-
Ca
-
CuO
2
-
Ca
-
CuO
2
-
BaO block followed by a
single or a double TlO layer, respectively. Starting translation periods of the

intergrowth
structures were calculated from the formula:
c
int
=n∙
c
Tl
-
1223
+m∙
c
Tl
-
2223
/2, where n and m are
the numbers of Tl
-
1223 and Tl
-
2223 stacking units in the intergrowth, respectively.


For the Tl
-
1223 phase all atomic positional parameters of the met
al and oxygen
atoms were refined. Due to peak broadness and the low weight content, some parameters of
the other phases were constrained or fixed. For Tl
-
2223 and the intergrowth phases, the
positional parameters of the metal sites were refined, whereas th
e parameters of the oxygen
positions were constrained with respect to the metal sites. Isotropic displacement parameters
were fixed at 2.0 Å
2

for the metal atoms and 1.0 Å
2

for oxygen in

Tl
-
2223 and the
intergrowth phase. The partial occupation of the Ca s
ite by Tl was constrained to be equal in
all phases. The unit cell parameter in the direction of the stacking of atom layers was refined
for all phases. The unit cell parameter in the direction parallel to the atom layers was
constrained for the intergrowt
h phase to be equal to that of the Tl
-
1223 unit cell. The
occupancies of the Tl sites were refined separately in all phases. All oxygen sites were
assumed to be fully occupied. The Tl and O positions in the TlO layers in Tl
-
1223 were
split. The Tl
-
1223 pha
se showed preferred orientation in the 001 direction with a parameter
of the March
-
Dollase function of about 0.5.


In the refinements of the intergrowth structures, all

BaO
-
CuO
2
-
Ca
-
CuO
2
-
Ca
-
CuO
2
-
BaO
blocks

were assumed to be identical and local mirror plane
s were introduced at the
central CuO
2

planes. The refinements of these models were carried out in several stages.
First the expansion of the BaO
-
CuO
2
-
Ca
-
CuO
2
-
Ca
-
CuO
2
-
BaO block and the position of the
single TlO layer were refined, and then the individual p
ositions of the layers with respect to
the local mirror planes were refined. The positions of the double TlO layers were refined
independently.


The atomic scattering factors and correlation terms for anomalous dispersion were
those used by the DBWS
-
980
7 program. The refinements were based on diffraction data in


STRUCTURAL REFINEMENTS ON INTERMEDIATE PHASES Tl
-
1223


Tl
-
2223

23


the range 8<2

<90°, containing 91 reflections of Tl
-
1223, 103 of Tl
-
2223 and 275 of Tl
-
1223/1223/2223, excluding the low
-
angl
e region 4<2

<8°.


The X
-
ray diffraction study indicates that all four samples mainly contain
superconducting phases. This was confirmed by magnetic measurements. Traces of BaCuO
2

and Ca
2
CuO
3

and some unidentified phases were detected, but we deduce that t
heir overall
amounts do not exceed 5%. In addition to Tl
-
1223, all samples were found to contain
significant amounts of Tl
-
2223. This is in agreement with earlier works, where the
formation path of unsubstituted Tl
-
1223 is considered to go through Tl
-
2223
[1]. From the
diffraction patterns of samples prepared at different temperatures (Fig. 1) it can be seen that
the complete transformation of Tl
-
2223 to Tl
-
1223 has taken place at temperatures higher
than 920°C after a 12 h treatment in sealed tube. The com
pleteness of the transformation
can be achieved at lower temperatures by applying several subsequent treatments with
intermediate grindings (see TB910). The low
-
angle diffraction peak of the Tl
-
2223 phase
shown in Fig.1 is broad, due to the grain morpholog
y and an inhomogeneous content of Tl.
A detailed profile study of the low
-
angle diffraction peaks and the Rietveld refinement lead
to the conclusion that the peak broadness is caused by the existence of average structures
(intergrowth) between Tl
-
1223 and
Tl
-
2223, which can be intermediate in the course of the
formation of the Tl
-
1223 phase. Other intense diffraction peaks also belong to the
intergrowth phase
: 29.0, 32.8, 34.7, 36.6° of 2θ Cu
K
α. With increasing temperature and/or
number of treatment stages the amount of intergrowth phase decreases like that of Tl
-
2223.
The refinement of the Tl
-
2223 phase is significantly improved when the presence of an
interg
rowth structure is taken into consideration.

890°C
900°C
910°C
920°C
1 - 002 Tl-2223
2 - 006 Tl-1223/1223/2223
3 - 001 Tl-1223
1
2
3


Fig. 1. Diffraction pattern in the region 4
-
8° of 2θ Cu
K
α
for samples treated at different temperatures

24

O. Shcherban, Th. Hopfinger, R. Gladyshevskii et al.


Table 2

Structu
ral characteristics of Tl
-
1223, Tl
-
2223

and possible intergrowths

Phase

Composition

Tl content,
at.%

Pearson code

Space group

a
,
c
, Å

Main peak,

2θ Cu
K
α (
hkl
)

Tl
-
1223

TlBa
2
Ca
2
Cu
3
O
9

5.882

tP
17

P
4/
mmm

3.8463(2)

15.8584(5)

5.568 (001)

Tl
-
1223/1223/2223

Tl
4
Ba
6
Ca
6
Cu
9
O
28

7.547

tI
106

I
4/
mmm

3.8463(2)

98.45(2)

5.382 (006)

Tl
-
1223/2223

Tl
3
Ba
4
Ca
4
Cu
6
O
19

8.333

tI
72

I
4/
mmm

3.8463

67.31

5.247 (004)

Tl
-
1223/2223/2223

Tl
5
Ba
6
Ca
6
Cu
9
O
29

9.091

tP
55

P
4/
mmm

3.8463

51.81

5.113 (003)

Tl
-
2223

Tl
2
Ba
2
Ca
2
Cu
3
O
10

10.526

tI
38

I
4/
mm
m

3.844(3)

35.909(7)

4.918 (002)



Tl
-
1223 and Tl
-
2223 are members of the Tl
-
based family of high
-
T
c

superconduc
-
tors. The Tl
-
12(n
-
1)n and Tl
-
22(n
-
1)n structure series differ in the number of TlO layers in
the structure, which consists of a stacking of Ba
O
-
CuO
2
-
[Ca
-
CuO
2
]
n
-
1
-
BaO perovskite
-
deri
-
ved blocks and single or double TlO rocksalt layers. The crystal structures of the inter
-
growth phases are also built of such BaO
-
CuO
2
-
[Ca
-
CuO
2
]
n
-
1
-
BaO blocks separated by TlO
or TlO
-
TlO layers. We have tested three
possible simple models of intergrowth with the
ratios of Tl
-
1223 to Tl
-
2223 stacking units 2:1, 1:1 and 1:2 (Tl
-
1223/1223/2223, Tl
-
1223/
2223 and Tl
-
1223/2223/2223), other models are considered in [6]. Structural characteristics
are given in Table 2. Depen
ding on the parity of the number of stacking layers, the space
group of the intergrowth structure is primitive or body
-
centered tetragonal. The Tl content
increases with increasing number of double layers TlO. The composition is calculated assu
-
ming full o
ccupancy of the Tl site, but double TlO layers are in general partially occupied,
which can be explained by TlO deintercalation during the formation of Tl
-
1223 from Tl
-
2223. The structures of the intergrowth phases mentioned here are presented in Fig. 2. T
he
schematic drawings show the sequence of Tl
-
1223 and Tl
-
2223 (half unit cell) stacking
units. Calculated diffraction patterns of the same intergrowth phases are presented in Fig.3.
During the refinement of the intergrowth structures, local mirror planes
were assumed
through the middle CuO
2

and single TlO layers. The introduction of a second TlO layer
causes a shift of the BaO
-
CuO
2
-
Ca
-
CuO
2
-
Ca
-
CuO
2
-
BaO block in the neighboring stacking
unit by ½ ½ parallel to the atom layers. The opposite shift must take pl
ace during the TlO
layer deintercalation in order to transform Tl
-
2223 to Tl
-
1223. Atom sites for Tl
-
1223, Tl
-
2223 and Tl
-
1223/1223/2223 are given in Table 3. Refinements considering two other
models of intergrowth led to higher reliability factors, incons
istent Tl
-
occupations and
interlayer distances.


Weight fractions, refined unit cell parameters, fractional atomic coordinates,
isotropic displacement parameters and site occupancies of Tl
-
1223, Tl
-
2223 and Tl
-
1223/1223/2223 are given in Tables 4, 6 and 8.

Interatomic distances and metal
-
metal
interlayer distances are given in Tables 5, 7 and 9.


The unit cell parameters of Tl
-
1223 and Tl
-
2223 are in agreement with literature
data. The
a
-
parameter of Tl
-
2223 is slightly smaller than that of Tl
-
1223, but wit
hin the
limits of esd. The
a
-
parameter of the intergrowth phase is close to that of Tl
-
1223 and was

STRUCTURAL REFINEMENTS ON INTERMEDIATE PHASES Tl
-
1223


Tl
-
2223

25

y 0 1/2
Tl
Ba
Ca
Cu
O
1
2
2
3
Ca
Ca
BaO
BaO
TlO
a
2
2
2
3
2
2
2
3
Ca
Ca
Ca
Ca
BaO
BaO
BaO
BaO
TlO
TlO
TlO
TlO
b
1
2
2
3
1
2
2
3
2
2
2
3
2
2
2
3
c
1
2
2
3
1
2
2
3
1
2
2
3
2
2
2
3
2
2
2
3
d
1
2
2
3
1
2
2
3
1
2
2
3
1
2
2
3
2
2
2
3
2
2
2
3
e


Fig. 2. Schematic drawings of Tl
-
1223
(
a
)

and Tl
-
22
23
(
b
)
, and possible inter
-
growth structures: Tl
-
1223/2223/2223
(
c
)
, Tl
-
1223/2223
(
d
)
, Tl
-
1223/1223/2223
(
e
)

26

O. Shcherban, Th. Hopfinger, R. Gladyshevskii et al.

5
1
0
1
5
2
0
2
5
3
0
3
5
4
0
4
5
0
0
6
0
0
1
0
0
2
0
0
3
0
0
4
1
0
0
1
0
1
1
0
2
0
0
5
1
0
3
1
0
4
1
1
1
1
1
2
1
0
5
0
0
7
1
1
4
1
0
6
1
1
5
1
1
0
1
1
3
0
0
2
0
0
4
0
0
6
0
0
8
1
0
1
1
0
3
1
0
5
0
0
.
1
0
1
0
7
0
0
.
1
2
1
0
9
1
1
0
1
1
4
0
0
.
1
4
1
0
.
1
1
1
1
6
1
1
8
0
0
.
1
6
1
1
.
1
0
1
0
.
1
5
1
1
2
0
0
3
0
0
4
0
0
5
0
0
6
0
0
7
0
0
8
0
0
9
0
0
.
1
0
0
0
.
1
1
0
0
.
1
2
0
0
.
1
3
1
0
0
0
0
.
1
4
1
0
5
1
0
6
1
0
7
1
0
8
1
0
9
1
0
.
1
0
1
0
.
1
1
0
0
.
1
8
1
0
.
1
3
1
1
5
1
0
.
1
5
1
1
8
1
0
.
1
8
0
0
.
2
3
1
1
.
1
4
0
0
.
2
4
0
0
.
2
0
0
0
.
1
5
0
0
.
1
6
0
0
.
1
7
1
0
.
1
2
0
0
.
1
9
1
1
0
1
1
3
1
0
.
1
6
0
0
.
2
1
1
0
.
1
7
0
0
.
2
2
0
0
.
2
5
1
0
.
2
1
0
0
4
0
0
6
0
0
8
0
0
.
1
0
0
0
.
1
2
0
0
.
1
4
0
0
.
1
6
1
0
1
0
0
.
1
8
1
0
5
1
0
7
1
0
9
1
0
.
1
1
1
0
.
1
3
0
0
.
2
2
1
0
.
1
5
0
0
.
2
4
1
0
.
1
7
1
1
4
1
0
.
1
9
0
0
.
2
6
1
1
.
1
0
1
0
.
2
1
0
0
.
2
8
1
0
.
2
3
1
1
.
1
6
0
0
.
3
0
1
0
.
2
5
1
1
.
2
0
1
0
3
0
0
.
2
0
1
1
0
1
1
6
1
1
.
1
2
1
1
.
1
4
1
1
.
1
8
0
0
.
3
2
1
0
.
2
7
0
0
6
0
0
8
0
0
.
1
0
0
0
.
1
2
0
0
.
1
4
0
0
.
1
6
0
0
.
1
8
0
0
.
2
0
0
0
.
2
2
0
0
.
2
4
1
0
1
0
0
.
2
6
1
0
7
1
0
.
1
1
1
0
.
1
3
1
0
.
1
5
1
0
.
1
7
1
0
.
1
9
1
0
.
2
1
0
0
.
3
4
1
0
.
2
5
1
0
.
2
7
1
1
.
1
0
1
0
.
2
9
1
1
.
1
6
0
0
.
4
0
1
1
.
1
8
1
1
.
2
0
1
1
.
2
2
1
0
.
3
5
0
0
.
4
4
1
1
.
2
6
1
1
.
2
8
1
0
.
3
9
0
0
.
4
8
0
0
.
2
8
1
0
9
0
0
.
3
0
0
0
.
3
2
1
0
.
2
3
0
0
.
3
6
1
1
0
1
1
6
0
0
.
3
8
1
0
.
3
1
0
0
.
4
2
1
0
.
3
7
0
0
.
4
6
1
1
.
3
0
1
1
.
3
2
Tl-1223
Tl-1223/1223/2223
Tl-1223/2223
Tl-1223/2223/2223
Tl-2223


Fig. 3. Calculated diffraction patterns of Tl
-
1223, Tl
-
1
223/1223/2
223, Tl
-
1223/2223, Tl
-
1223/
2223/2223 and Tl
-
2223 in the region 4
-
45° of 2θ Cu
K
α (
hkl

of intense diffraction peaks are given)

Table 3

Models for Tl
-
1223, Tl
-
2223 and Tl
-
1223/1223/2223

(Wyckoff position and fractional atomic coordinates are given for each
site)

Tl
-
1223


Tl
-
1223/1223/2223

Tl

4(
l
)

x

0 0

O(1)

4(
n
)

x

½ 0


Cu(1)

2(
a
)

0 0 0

O(1)

4(
c
)

0 ½ 0

Ba

2(
h
)

½ ½
z

O(2)

2(
h
)

½ ½
z


Ca(1)

4(
e
)

½ ½
z




Cu(1)

2(
g
)

0 0
z

O(3)

4(
i
)

0 ½
z


Cu(2)

4(
e
)

0 0
z

O(2)

8(
g
)

0 ½
z

Ca

2(
h
)

½ ½
z





Ba(1)

4(
e
)

½ ½
z

O(
3)

4(
e
)

0 0
z

Cu(2)

1(
b
)

0 0 ½

O(4)

2(
e
)

½ ½ ½


Tl(1)

4(
e
)

0 0
z

O(4)

4(
e
)

½ ½
z








Ba(2)

4(
e
)

½ ½
z

O(5)

4(
e
)

0 0
z








Cu(3)

4(
e
)

0 0
z

O(6)

8(
g
)

0 ½
z

Tl
-
2223


Ca(2)

4(
e
)

½ ½
z




Tl

4(
e
)

0 0
z

O(1)

4(
e
)

½ ½
z


Cu(4)

4(
e
)

0 0
z

O(7)

8(
g
)

0
½
z

Ba

4(
e
)

½ ½ z

O(2)

4(
e
)

0 0
z


Ca(3)

4(
e
)

½ ½
z




Cu(1)

4(
e
)

0 0
z

O(3)

8(
g
)

0 ½
z


Cu(5)

4(
e
)

0 0
z

O(8)

8(
g
)

0 ½
z

Ca

4(
e
)

½ ½
z





Ba(3)

4(
e
)

½ ½
z

O(9)

4(
e
)

0 0
z

Cu(2)

2(
b
)

0 0 ½

O(4)

4(
c
)

0 ½ ½


Tl(2)

4(
e
)

0 0
z

O(10)

4(
e
)

½ ½
z

Table 4

W
eight fraction (WF), unit cell parameters, fractional atomic coordinates, isotropic displacement
parameters (
B
, Å
2
) and site occupancies (
occ
) in the structure of Tl
-
1223

Parameter

TB890

TB900

TB910

TB920

1

2

3

4

5

WF, %

70(1)

82(1)

96(1)

90(2)

R
P

0.041
3

0.0380

0.0373

0.0444

R
WP

0.0584

0.0528

0.0532

0.0608

STRUCTURAL REFINEMENTS ON INTERMEDIATE PHASES Tl
-
1223


Tl
-
2223

27

End of Tabl. 4

1

2

3

4

5

R
B

0.0772

0.0885

0.1244

0.1082

a
, Å

3.8463(2)

3.8446(1)

3.8453(1)

3.8461(2)

c
, Å

15.8584(5)

15.8560(4)

15.8641(6)

15.8543(7)

V
, Å
3

234.61(2)

234.36(1)

234.58(1)

234.52(1)

x
Tl *

0.074(6)

0.02(2)

0.05(2)

0.057(8)

z
Ba

0.1707(1)

0.1717(1)

0.1717(1)

0.1717(2)

z
Cu(1)

0.2979(4)

0.2980(3)

0.3003(3)

0.2988(4)

z
Ca

0.3955(4)

0.3967(3)

0.4015(4)

0.4002(6)

z
Cu(2)

1/2

1/2

1/2

1/2

x
O(1) **

0.649(6)

0.54(2)

0.60(2)

0.614(8)

z
O(2)

0.135(1)

0.134(1)

0.131(1)

0.142(2)

z
O(3)

0.303(1)

0.3025(7)

0.3071(8)

0.3097(9)

z
O(4)

1/2

1/2

1/2

1/2

B
Tl

1.5(2)

1.5(2)

1.6(2)

1.6(2)

B
Ba

2.3(2)

1.8(1)

2.3(1)

1.7(2)

B
Cu(1)

1.6(3)

0.7
(2)

0.9(2)

0.5(3)

B
Ca

1.2(4)

0.5(3)

0.5(4)

1.0(5)

B
Cu(2)

1.4(3)

1.8(2)

1.1(3)

0.7(3)

occ
Tl *

0.243(2)

0.246(1)

0.225(2)

0.243(2)

occ
O(1) **

1/4

1/4

1/4

¼

occ
Ca/Tl

0.935(6)

0.065

0.942(5)

0.058

0.957(6)

0.043

0.979(7)

0.021


*Tl was refined in 4(
l
)
x

0 0 position instead of 1(
a
) 0 0 0


**O(1) was refined in 4(
n
)
x

½ 0 position instead of 1(
c
) ½ ½ 0 with occupation parameter


fixed at ¼;
x
O(1) was constrained:
x
O(1)=1/2+2∙
x
Tl.

Table 5

Metal
-
oxygen interatomic distances and metal
-
metal i
nterlayer distances for Tl
-
1223

Atoms

TB890

TB900

TB910

TB920

1

2

3

4

5

6

Tl

2 O(2)

2.160

2.118

2.151

2.262


2 O(1)

2.199

2.586

2.336

2.302

Ba

1 O(1)

2.767

2.725

2.751

2.757


4 O(2)

2.778

2.785

2.781

2.760


4 O(3)

2.846

2.828

2.883

2.912

Cu(1)

4 O(3
)

1.924

1.924

1.926

1.931


1 O(2)

2.583

2.608

2.624

2.486

Ca

4 O(3)

2.418

2.434

2.437

2.399


4 O(4)

2.538

2.526

2.478

2.490

Cu(2)

4 O(4)

1.923

1.922

1.923

1.923

Tl

Ba

2.707

2.722

2.724

2.722

Ba

Cu(1)

2.017

2.003

2.040

2.015

Cu(1)

Ca

1.548

1.565

1.60
5

1.608

Ca

Cu(2)

1.657

1.638

1.563

1.582

Cu(1)

Cu(2)

3.205

3.203

3.168

3.190




28

O. Shcherban, Th. Hopfinger, R. Gladyshevskii et al.


Table 6

Weight fraction (WF), unit cell parameters, fractional atomic coordinates and site
occupancies (
occ
) in the

structure of Tl
-
2223. The isotropic displacement
parameters were fixed at 2.0 Å
2

for metals, 1.0 Å
2

for oxygen

Parameter

TB890

TB900

TB920

WF, %

13(5)

2(26)

2(29)

R
B

0.1156

0.1685

0.2775

a,
Å

3.844(3)

3.84(1)

3.84(2)

c
, Å

35.909(7)

35.98(4)

35.98(6)

V
, Å
3

530.5(5)

529(3)

529(4)

z
Tl,
z
O(1)

0.2799(5)

0.282(3)

0.274(3)

z
Ba,
z
O(2)

0.3479(4)

0.345(3)

0.342(3)

z
Cu(1),
z
O(3)

0.4107(8)

0.406(5)

0.407(4)

z
Ca

0.458(1)

0.459(5)

0.459(11)

z
Cu(2),
z
O(4)

1/2

1/2

½

occ
Tl

0.70(3)

0.9(2)

1.0

occ
Ca/Tl

0.935(6)

0
.065

0.942(5)

0.058

0.979(7)

0.021


Table 7

Metal
-
oxygen interatomic distances and metal
-
metal interlayer distances for Tl
-
2223

Atoms

TB890

TB900

TB920

Tl

1 O(2)

2.441

2.268

2.482


4 O(1)

2.718

2.718

2.720

Ba

1 O(1)

2.441

2.268

2.483


4 O(2)

2.718

2.7
18

2.720


4 O(3)

2.963

2.917

3.028

Cu(1)

4 O(3)

1.922

1.922

1.923


1 O(2)

2.255

2.195

2.339

Ca

4 O(4)

2.443

2.422

2.424


4 O(3)

2.564

2.708

2.683

Cu(2)

4 O(4)

1.922

1.922

1.923

Tl

Tl

2.147

2.230

1.655

Tl

Ba

2.442

2.267

2.482

Ba

Cu(1)

2.255

2.195

2
.339

Cu(1)

Ca

1.698

1.907

1.871

Ca

Cu(2)

1.508

1.475

1.475

Cu(1)

Cu(2)

3.206

3.382

3.346


constrained. The
c
-
parameter of the intergrowth phase is ~98.5 Å, which corresponds to an
average stacking unit of 16.42 Å. The largest amounts of Tl
-
2223 and int
ergrowth phase
were formed at 890

°C, 13 and 17 wt.%, respectively. In Tl
-
1223 the Tl site is located off
the four
-
fold axis by about 0.28 Å (for TB890). The O position in the TlO layer was refined
off center too and constrained with respect to the T
l position. The occupation parameter of
the Tl site refined to approximately ¼. The smallest value was obtained for TB910, the
sample submitted to several subsequent treatments. The octahedral coordination in the ideal
structure of 1223 superconductors is
for Tl transformed to tetrahedral (Fig.

4). Partial
substitution of Ca by Tl atoms was detected; it equals 6.5 at.% for TB890 and decreases
with increasing temperature and corresponding Tl loss. Due to the site splitting, the Tl
-
O in
-
plane interatomic di
stances are short and close to 2.2 Å. The large Ba atoms have approxi
-

STRUCTURAL REFINEMENTS ON INTERMEDIATE PHASES Tl
-
1223


Tl
-
2223

29


Table 8

Weight fraction, unit cell parameters, fractional atomic coordinates and site occupancies
(
occ
) in the stru
cture of Tl
-
1223/1223/2223. The isotropic displacement parameters
were fixed at 2.0 Å
2

for metals, 1.0 Å
2

for oxygen

Parameter

TB890

TB900

TB920

WF, %

17(6)

15(7)

8(16)

R
B

0.1237

0.1690

0.2780

a,
Å

3.8463(2)

3.8446(1)

3.8461(2)

c,
Å

98.45(2)

98.36(3)

9
7.75(3)

V, Å
3

1456.6(2)

1453.8(4)

1446(1)

z
Cu(1),
z
O(1)

0

0

0

z
Ca(1)

0.0154(6)

0.0139(7)

0.0147(2)

z
Cu(2),
z
O(2)

0.0299(3)

0.0295(4)

0.0287(3)

z
Ba(1),
z
O(3)

0.0515(2)

0.0514(2)

0.0521(2)

z
Tl(1),
z
O(4)

0.0807(3)

0.0816(3)

0.0822(4)

z
Ba(2),
z
O(5)

0.10
99(2)

0.1117(2)

0.1123(2)

z
Cu(3),
z
O(6)

0.1315(3)

0.1336(4)

0.1356(3)

z
Ca(2)

0.1460(6)

0.1492(7)

0.1497(7)

z
Cu(4),
z
O(7)

0.1612(2)

0.1631(3)

0.1645(4)

z
Ca(3)

0.1765(6)

0.1770(7)

0.1791(7)

z
Cu(5),
z
O(8)

0.1910(3)

0.1926(4)

0.1932(3)

z
Ba(3),
z
O(9)

0.21
26(2)

0.2145(2)

0.2165(2)

z
Tl(2),
z
O(10)

0.2375(2)

0.2363(3)

0.2358(3)

occ
Tl(1)

0.88(6)

0.95(6)

1.0

occ
Tl(2)

0.97(5)

0.82(6)

1.0

occ
Ca/Tl

0.935(6)

0.065

0.942(5)

0.058

0.979(7)

0.021


mately spherical coordination with Ba
-
O distances close to 2.8 Å.

The Cu atoms in pyra
-
midal coordination are displaced off the plane. The distance from Cu to the apical O is about
2.6 Å for all samples. Ca and O form centered tetragonal prisms with Ca
-
O distances ~2.5Å.
It is remarkable that for the samples with a high

Tl content at the Ca site, Ca is displaced
closer to Cu with pyramidal coordination, where as in the samples with less than 5

at.

% Tl
at the Ca site, Ca is closer to Cu with square planar coordination. The oxygen atoms of the
BaO layers are attracted by
Tl and displaced off the Ba layers by 0.5 Å. The isotropic
displacement parameter for Tl is close 1.6 Å
2
; a larger value is observed for the Ba atoms,
~2.0 Å
2
, a smaller value for the Ca atoms.


The refinement of the Tl
-
2223 phase
was difficult due to its
low content and
considerable peak overlap. Only at 890

°C
a significant amount of Tl
-
2223 was found.
At higher temperatures it was not larger
than 2 wt.%, and after the complex thermal
treatment (sample TB910) the quantity of
this phase was too small to be

considered.
The occupancy of the Tl site was 70% for
TB890 and 90% for TB900 (for TB920 it
was not refined). The Tl
-
Tl interlayer dis
-
tance is close to 2.2 Å, which is in agree
-
ment with literature data and is close to the


Fig. 4. Splitting o
f atom positions in a
TlO layer of the Tl
-
1223 structure (a TlO
4

tetra
-
hedron is shown)

30

O. Shcherban, Th. Hopfinger,

R. Gladyshevskii et al.


Table 9

Metal
-
oxygen interatomic distances and metal
-
metal interlayer distances for Tl
-
1223/1223/2223

Atoms

TB890

TB900

TB920

Cu(1)/Cu(4)

4 O(1)/O(7)

1.923

1.922

1.923

Ca(1)/Ca(2)/Ca(3)

4 O(2)/O(6)/O(8)

2.395

2.460

2.360


4 O(
1)/O(7)/O(7)

2.436

2.359

2.401

Cu(2)/Cu(3)/Cu(5)

4 O(2)/O(6)/O(8)

1.923

1.922

1.923


1 O(3)/O(5)/O(9)

2.116

2.154

2.287

Ba(1)/Ba(2)/Ba(3)

4 O(3)/O(5)/O(10)

2.719

2.719

2.720


4 O(2)/O(6)/O(9)

2.867

2.887

2.942


1 O(4)/O(4)/O(8)

2.884

2.971

2.988

Tl(1
)

4 O(4)

2.719

2.719

2.720


1 O(5)

2.884

2.961

2.932


1 O(3)

2.884

2.971

2.942

Tl(2)

1 O(9)

2.451

2.144

1.906


4 O(10)

2.719

2.719

2.720

Cu(1)/Cu(4)/Cu(4)

Ca(1)/Ca(2)/Ca(3)

1.506

1.367

1.437

Ca(1)/Ca(2)/Ca(3)

Cu(2)/Cu(3)/Cu(5)

1.428

1.534

1.369

Cu(2
)/Cu(3)/Cu(5)

Ba(1)/Ba(2)/Ba(3)

2.127

2.154

2.287

Ba(1)/Ba(2)

Tl(1)/Tl(1)

2.875

2.970

2.933

Ba(3)

Tl(2)

2.451

2.144

1.906

Tl(2)

Tl(2)

2.461

2.695

2.776

Cu(1)/Cu(3)/Cu(5)

Cu(2)/Cu(4)/Cu(4)

2.933

2.921

2.806



1
2
3

Fig. 5. Ob
served (dotted), calculated (line) and difference (bottom) patterns for the sample
TB890. The contribution of the Tl
-
1223/1223/2223 intergrowth phase is shown below the main
pattern


STRUCTURAL REFINEMENTS ON INTERMEDIATE PHASES Tl
-
1223


Tl
-
2223

31


valu
e calculated from the difference between the
c
-
parameters of Tl
-
1223 and Tl
-
2223. The
Tl
-
Ba interlayer distance (2.4 Å) is smaller than for Tl
-
1223 (2.7 Å), which is a well
-
known
fact. These differences observed between single and double TlO layers are ref
lected in the
intergrowth structure. The distance from Cu to the apical O is 2.25 Å, which is smaller than
for Tl
-
1223.


Quite large quantities of intergrowth phases were observed in all samples prepared in
sealed tubes. After the procedure with several
treatments and intermediate grindings, inter
-
growth was not observed. The average
c
-
parameter of the intergrowth phases was found to
decrease with decreasing amount of intergrowth. The Tl occupancy was refined for the
TB890 and TB900 samples and was close
to 90% for both single and double TlO atom
layers. An analysis of the interatomic distances revealed that the structure of the intergrowth
phase reflects some regularities noted in the structures of Tl
-
1223 and Tl
-
2223. The Tl
-
Ba
interlayer distance is

shorter for the stacking unit containing double TlO layers, the values
being close to those observed in Tl
-
1223 and Tl
-
2223.


The diffraction patterns for the TB890 sample in the region 8
-
70° of 2θ Cu
K
α are
shown in Fig.5. The difference pattern presented at the bottom indicates good reliability of
the refinement of the intergrowth phase, an individual diffraction pattern of whi
ch is
presented in the same figure.

__________________________


1.
Jorda

J.L., Hopfinger

Th., Couach

M., Pugnat

P., Bertrand C.

and Galez Ph.

Formation
of Thallium
-
1223 Superconductors // J. Supercond. 1998. Vol.11
.

No

1. P.87
-
89.

2.
Young

R.A., Sakthivel

A., Moss T.S.

and Paiva
-
Santos

C.O.

DBWS
-
9411


an Upgrade of
the DBWS*.*. Programs for Rietveld Refinement with PC and Mainframe Computers

// J. Appl. Crystallogr. 1995. Vol.28. P.366
-
367.

3.
Kawashima

S., Inoue O.

and Adachi

S.
, Superlattice Structure o
f TlBa
2
Ca
2
Cu
3
O
y

and
Tl
2
Ba
2
Ca
2
Cu
3
O
y

(c/2) // Jpn. J. Appl. Phys. 1990. Vol.29
.

No

6. P.L900
-
L901.

4.
Zhang

X.F., Sung Y.S.

and Miller

D.J.

Special Tl

Ba

Ca

Cu

O Structures: Two
Intermediate States and their Superconducting Behavior // Physica C. 1998. Vol.3
01.
P.221
-
233.

5.
Gladyshevskii R.E.

and Galez

Ph.

Crystal Structures of High
-
T
c

Superconducting
Cuprates // Handbook of Superconductivity, Ed. Ch. P. Poole, Jr., San Diego: Academic
Press, 2000. Ch.8. P.267
-
431.

6.
Hopfinger

Th., Shcherban O.O., Galez

Ph.
, Gladyshevskii

R.E., Lomello
-
Tafin

M., Jor

da J.L.

and Couach

M.

Intergrowth of Structures in the Tl
-
Ba
-
Ca
-
Cu
-
O System // J.
Alloys. Compd
.
2002. Vol.333. P.237
-
248.













32

O. Shcherban, Th. Hopfinger, R. Gladyshevskii et al.


ВИЗНАЧЕННЯ СТРУКТУРИ ПРОМІЖНИХ ФАЗ
Tl
-
1223


Tl
-
2223


O
.
Щербан
1
,
Т.

Хопфінгер
2
,
Р
.
Гладишевський
1
,
Ф
.
Галез
2
,
Ж
.
Л
.
Жорда
2


1
Львівський національний університет імені Івана Франка
,

вул. Кирила і Мефодія, 6, 79005 Львів, Україна


2
Університет Савуа,
BP
240,

F
-
74942 Ансі, Франція



У системі Tl
-
Ba
-
Ca
-
Cu
-
O з’ясовано утворення проміжної фази Tl
4
Ba
6
Ca
6
Cu
9
O
28
. Мето
-
дом порошку визначено її кристалічну структуру (
I
4/
mmm
,
a
=3,8463,
c
=98,45

Å,
Z
=2), яку
можна розглядати як гомологічну структуру побудовану з фрагмент
ів Tl
-
1223 та Tl
-
2223 у
співвідношенні 2

:

1. Наведено структурні моделі інших проміжних фаз, утворення яких також
можливе при переході від Tl
-
2223 до Tl
-
1223 шляхом послідовної деінтеркаляції шарів TlO.



Ключові слова
: високотемпературні надпровідники, с
истема Tl
-
Ba
-
Ca
-
Cu
-
O, гомологічна
структура.


Стаття надійшла до редколегії 28.11.2002

Прийнята до друку 10.02.2003