Structure of Ba2InCuOy: A new layered cuprate with a blocking layer of BaInOy perovskite

PHYSICA

Physica C 220 (1994) 119-126 North-Holland

Structure of Ba2InCuOy: a new layered cuprate with a blocking layer of BaInOy perovskite Shiro K a m b e , I s a o Shime, Shigetoshi O h s h i m a a n d K a t s u r o O k u y a m a Department of Electronic and Information Engineering, Faculty of Engineering, Yamagata University, 4-3-16 Jonan, Yonezawa992, Japan

N a o y u k i O h n i s h i a n d Kenji H i r a g a Institutefor Materials Research, Tohoku University, 2-1-1 Katahira, Sendal 980, Japan

Received 8 October 1993

A new blocking layer with an a-axis length of 4.18 ~., Ba|nOy, was found. The blocking layer supplies an apical oxygen to the CuO2 layer and produces an oxygen vacancy in the in-plane of the CuO2 layer. By matching the blocking layer with the CuO2 layer, a new layered cuprate, Ba21nCuO4.33,was prepared. Its space group was Pmmm with lattice parameters of a = 4.1820 ( 6 ) A, b= 4.1820(5) ~ and c= 8.0889 (9) A. The fact that the a- and b-axis lengths of Ba21nCuO4.s3compound are much longer than those of the other cuprate compounds is explained by the existence of an oxygenvacancy in the CuO2layer. Its resistivity at room temperature was as large as 28.8 Mfl cm. The insulating property probably comes from the existence of the oxygenvacancy in the CuO2 layer.

I. Introduction Since the L a - B a - C u - O superconductor was discovered [ 1,2], much effort has been devoted to exploring new superconducting oxide compounds with higher transition temperatures. The effort led to the discovery of Y - B a - C u - O [3] ( T c = 9 2 K), B i - S r C a - C u - O [4] (T~=107 K), T I - B a - C a - C u - O [5] ( T c = 1 2 5 K) and H g - B a - C a - C u - O [6] ( T c = 1 3 3 K) and dozens o f related materials. From the already known cuprate superconductors, we view a c o m m o n structural feature. Each cuprate superconductor is composed of a two-dimensional structure with both a CuO2 and a blocking layer. Superconductivity occurs when the CuO2 layer is doped with an appropriate density of charge carriers. On the other hand, the blocking layer plays a role of charge reservoir as well as isolating the CuO2 layer. The structure of the blocking layer is classified as NaC1 type ( L a - B a - C u - O system, La202 layer; B i - S r - C a C u - O system, Bi202 layer; T 1 - B a - C a - C u - O system, T1202 layer), CaF2 type ( N d - C e - C u - O system, Nd202 layer) [7], oxygen-defect perovskite type ( Y -

B a - C u - O system, BaCuOy), and non-cuprate perovskite type ( Y - S r - G a - C u - O system, SrGaO2 layer) [8,9 ]. After the introduction o f the concept of the blocking layer by Tokura et al. [ 10 ], (M, Cu) Sr2 (Ln, Ce),CuzO2n+5 (M=T1, Pb) [11,12], Bi2Srz(Eu, Ce)2Cu2OIo [13] and (Ba, Eu)z(Eu, Ce)2Cu3Os+x [ 14 ] superconductors were found, indicating that the classification scheme is very effective for designing new CuO2-1ayered compounds by combining an already known blocking layer with the CuO2 layer. However, there is an unsolved problem. We do not know exactly how to find an unknown blocking layer. We think that one o f the most important factors to determine the stacking limitation is the misfit between the blocking layer and the CuOz layer, that is, the difference between ab (the lattice parameter " a " of the blocking layer) and ac (that of the CuO2 layer) as shown in fig. 1. If the misfit between ab and ac is larger than the limitation (ab < ac or ab > ac), the c o m p o u n d will lead to separation into two different component parts. The purpose of this paper is to present the matching limitation between the CuO2 and the blocking

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S. Kambe et al. / Structure qf Ba fln('uO,

120

Blocking Layer

CuO: ABO~ %:3.7'0 4. IS,\

(Blocking Layer)

l.ayer ] 4.2O i

ab

B ,,i|e ion,, Mn Ga

\

Ti

Ru

Nb, hl Sn,'la Baln():-

(CuO: Layer)

~

BaCuO> :k "" 35)3,\ 4.15 3.95

(Blocking Layer)

SrRuO,

LaTiO~

BaCuO.,+ABO

('dSnO AgTaO~ NaNbO, CaSnO~

BiMnO,

P,aCuO: 'q '

l,aRuO~

~Sr'riO~ ;CeVO~ 33)(: I[-~ 2,.::~ - NdVO; r.UHU~- PrVO* :SmVO~

La(iaO,

(_idV()~

CeGaO PrGaO

BaCuO~+AB(),

NdGaO, 3.85

CuO-" CdTiO~

\BO

Fig. 1. The scheme of alternate stacking of the blocking and the

l.aSn()

C u O 2 layer.

layers and to show cuprate compounds with a new blocking layer. As a blocking layer, we chose non-cuprate perovskite compounds, because they are rich in a variety and their lattice parameter a is controlled successively between 3.79 and 4.18 ~ by changing the A and B site ions. As a CuOz layer, we chose a BaCuO2 ( a ~ 3.93/~, estimated from (Sr2/3 Ba~/3)CuO2 [ 15 ] ) layer, which is known as a typical CuO2 layer. Based on the concept, we found a new cuprate compound, Ba2InCuO4.53, with a blocking layer of BaInO r Its lattice parameter is as large as 4.18 A for a- and b-axis lengths. The extremely long a- and b-axis lengths are discussed in connection with the oxygen vacancy in the CuO2 layer.

Fig. 2. Matching of various non-cuprate perovskite compounds ( A B O 3 _ v ) with the BaCuO2 layer. The vertical axis in the figure stands for the a-axis length of ABO3_,. and columns are separated according to the element of lhe B site cations in a ABO~ , compound.

C

¢D

;5 ,2

5,3

100

2Q 0

~]O C 2 iJ

2. Experimental As a blocking layer, we picked a non-cuprate perovskite compound represented by ABO3_v with a lattice parameter a of 3.79-4.18 A (fig. 1 ). Starting powders were prepared by mixing BaCO3, CuO, "A"

40 0

~

z

50 0

;(' 0

(deg.)

Fig. 3. X-ray diffraction pattern of Ba2InCuO4.s>

element carbonate (or an oxide) and "'B" element oxide with the molar ratio of 1 : 1 : 1 : 1. The ratio leads to alternate stacking of the BaCuO2 and the ABO3 layers. For example, we tried to match BaInOz.5 [ 16 ]

S. Kambe et al. /Structure of BaelnCuOy

121

Fig. 4. Electron diffraction patterns of BazInCu04.53. (a = 4.18 A) with BaCuO2. The expected compound is expressed as BazlnCuOy. The powders of BaCO3, In203, and CuO with ethanol were ground in an agate mortar, calcined at 950°C for 5 h in air, and pressed into a pellet with a pressure of 400 kgf/cm 2. They were sintered several times at 970°C in air for 20 h. The other compounds were prepared in similar

conditions. The compositions of the compound were measured by ion-coupled plasma atomic emission spectroscopy (ICP-AES), with the result that the atomic ratio of the prepared sample deviated from that of the nominal one about 20%. Crystal structure was determined by powder X-ray diffraction at room temperature using C u K a

22

A'. K a m b e

ct a/

Structure" o t B a : l n ( ' u O ~

Fig. 5. High resolution TEM image of Ba2lnCuO4.~3 taken with the [010] incidence. ( a = 1.54056 ~ ) radiation. The step width was 0 . 0 2 in 20, and the scanning range was between 5 : and 60 ~. The X-ray diffraction data were analyzed using a Rietveld refinement p r o g r a m R I E T A N [ 17, 18 ]. By high resolution transmission electron microscopy ( H R T E M ) , electron diffraction patterns and atomic images were obtained. Oxygen content and average Cu valence were d e t e r m i n e d by the iodometric method. For example, the oxygen content and the Cu valence o f the Ba21nCuO,, were d e t e r m i n e d to be 4.53 and 2.06, respectively.

3. Results and discussion In fig. 2, matching of various non-cuprate perovskite c o m p o u n d s (ABO3_,~) with the BaCuO2 layer is shown. The vertical axis in the figure stands for the a-axis length o f ABO3 y and columns are separated according to the element of the B site cations in the ABO3_ v c o m p o u n d . A m o n g the candidates for blocking layers, LaRuO3 and BalnO2.5 with BaCuO: formed unknown single phases, Ba2InCuO,, (In syst e m ) and BaLaRuCuO~. (Ru system). [lnfortu-

nately, the structure of the Ru system is not a laxcrcd one c o m p o s e d o f the blocking and thc ('u()2 layers but a cubic one with a-axis length of 3.¢)2 -\. For the In system, the crystal structure was examined b\ X R D , ED, H R T E M and Rietveld analysis. In fig. 3. the X R D pattern flom the In system is shown. B\ putting a = b = 4 . 1 8 ,:~ and c = 8 . 0 8 .i. its pattern is completely assigned, suggesting that the In system is formed by alternate stacking o f the blocking and the CuO2 layers. In order to confirm the structure of Ba2InCuO4.5> electron diffractions ( E D ) wcrc observed (fig. 4). F r o m the [010] and [100] position> in the ED pattern of fig. 4 ( c ) , it was revealed that the a-axis length is nearly equal to the/J-axis length. On the other hand, the C-axis length is about twice as long as the a-axis length, as seen in fig. 41 a ). t::rom the X R D and ED patterns, the shape of the tlnit col[ was roughly,' confirmed. As illustrated in fig. I. the structure of the expected system is a double Perovskite structure with the alternate stack of the blocking and the CuO2 layers. Judging from the values of the cell parameters, the designed structure is realized in the In system, A H R T E M image of BaelnCu()<~3 taken with the

S. Kambe et al. /Structure of Ba2InCuOy

123

(i)

(a)

(b)

Fig. 6. Enlarged image of fig. 5 and the two probable structural models.

incident beam parallel to [010] is shown in fig. 5. The picture clearly displays the atomic arrangement of the structure and shows that the lattice parameters are a ~ 4.1 A and c ~ 8.0 A. The enlarged image in" fig. 6 presents two valuable keys to understanding the

structure. First, it is revealed that there are two different B sites. While the medium position between the B( 1 ) sites is brighter, that between the B(2) sites is darker. Considering that the structure of this compound is double Perovskite type, an oxygen is lo-

S. K a m b e et al. / Structure q f Ba f l n ( 'uO ~

124 Table 1 Crystallographic data for BazlnCuO4.s3

Model (a) Atom

Site

v

v

z

B( ,~-' )

Occupancx

Ba In(l ) In(2) Cu O( 1 ) 0(2) 0(3) 0(4) 0(5)

2t la lc lc lb le 2q Id lg

0.5 0 0 0 0.5 0 0 0.5 0

0.5 0 0 0

0.2408(3) 0 0.5 0.5

1.1524(2) 0.1781 (4) 3.8327(7) 1.1911 (9)

1 0.9809(9) 0.0700(9) 0.8073(7 )

0

0

(1.5

1

0.5 0 0 0.5

0 0.3026( 1 ) 0.5 0.5

0.5 0.5 0.5 0.5

1 I 0.265 0.265

Rwe=10.31%, Rp=7.97%, R1=2.75%, RF=2.29% and Re=8.51%. Space group P m m m ( N o . 47) wilh a = 4 . 1 8 2 0 ( 6 ) A, b=4.1820(5) ,~,, c=8.0889(9) ~i. Model (b) Atom

Site

x

y

z

B (.&2)

Occupanc>

Ba In( 1 ) In(2) Cu O(1) 0(2) O( 3 ) 0(4) 0(5)

2t lc Ic la lb le 2q ld Ig

0.5 0 0 0 0.5 0 0 0.5 (1

0.5 0 0 0 0 0.5 0 I~ 0.5

0.2648(0) 0.5 0 0 0 0 0.2480( 6 ) 0.5 (}.s

0.5 0.5 (/.5 0.5 0.5 (!.5 O.s 05 ~}q

1 0.9809(9) 0.0700(7) 0.8073( 7 ) I I

Rwp=14.30%, Rp=9.71%, Rx=7.83%, RF=6.18% and Re=8.52%. Space group P m n m l I N o a = 4 . 1 8 3 2 ( 0 ) ~, t,=4.1830( I ) A. c=8.0908(5 ) .t.

I

(L205 (1265 471 wilh

'Fable 2 Interatomic distances ( 4 ) t'or Ba:ln( u~ )45, Ba-Cu ( x 4 ) Ba-ln( 1 ) Ba-O( 1 I ( ×2~ - O ( 2 ) ( )< 2 ) -O(3) (x4) -()(4) ( x 2 ) -0(5) (X2) In(l) O(I) t;,2t - 0 ( 2 ) ()<2) -0(3)

c

v

cO (D

1:

[

.

.

[ II

[

I I

nl

:

>. I L

50

~

100

.

20.0

.

.

.

300 2 0

.

.

.

400

500

600

(deg.)

Fig. 7. XRD pattern of BazlnCuO4.s3. The dotted and solid lines represent the observed and calculated patterns, respectively. The line at the bottom is the difference between the observed and calculated intensities in the same scale.

~2649 :: 0.2242 3.5412 ~ 0.2295 2.8579 t I}.21)1~ 2.8579 ~ 0.201L! 2.9991~0.270q 2.9610 L~).1940 2.9610 t 0.1940 2.0910+0.274~, 2,0010±0.274" 2.4478+ 0.012'~

(7u-O ( 3 )

i. 5 9 6 7 * 0 . 0 1 2 0

-0(4) (X2) -0(5) (×2)

2.0910+0.2746 2.0910+0.2747

cated at the m e d i u m position b e t w e e n the B sites. resulting in the oxygen vacancy existing in lhe B( l ) layer. Actually, the oxygen content determined by the

S. Kambe et al. / Structure of Ba21nCuOv

125

Table 3 Indexed X-ray diffraction pattern of Ba21nCuO4.53 orthorhombic: P m m m ( N o . 47): a = 4 . 1 8 2 0 ( 6 ) A, b = 4 . 1 8 2 0 ( 5 ) A, c = 8 . 0 8 8 9 ( 9 ) A

I/Io

hkI

d~l~

dob.

00 1 0 10 1 00 002 0 11 10 1 1 10 0 12 10 2 111 003 112 0 13 10 3

8.088 4.182 4.182 4.044 3.714 3.714 2.957 2.907 2.907 2.777 2.696 2.387 2.266 2.266

8.051 4.172

13 5

4.030 3.711

4 3

2.951 2.901

65 100

2.771

3

2.383 2.261

10 7

0 vacancy

Cu

8a

In Ba

Cu

c

Fig. 8. Crystal structure of Ba2InCuO4.53. The occupancy of O (4) and 0 ( 5 ) sites are 26.5%.

iodometry was 4.53, which is consistent with the existence of the oxygen vacancy. Secondly, the distance between the A site and the B(2) layer. From these results, two probable models are presented at the bottom of fig. 6. While Cu and In atoms occupy the B( 1 ) and B(2) sites, respectively, in model (a), they occupy the reverse sites in model (b). A Ba atom occupies the A site for both models. In order to elucidate which of the two is the right one, Rietveld analysis was carried out for the two models. Refined crystallographic data for models (a) and (b) are listed in table 1. The reliability factors

hkI

d~.,~

dob.

I/Io

020 200 02 1 12 0 2 10 022 202 0 14 10 4 2 12 12 2 1 14 005

2.091 2.091 2.024 1.870 1.870 1.857 1.857 1.820 1.820 1.697 1.697 1.669 1.617

2.088

28

2.018 1.867

13 2

1.854

3

1.819

3

1.696

28

1.667 1.615

14 3

for the model (a) and (b) were Rwp= 10.3% and 14.3%, respectively. Refinement in model (a) converged with lower R values than that in model (b). In addition, the refined Ba positions for models (a) and (b) were (1 1 0.2403) and (½ 1 0.2648), respectively, indicating that the Ba site approached the I n - O planes for both models. From the HRTEM image, it is revealed that the Ba site shifts toward the B (2) layer. Consequently, it is concluded that model (a) stands for the right structure of Ba2InCuO4.53. As shown in fig. 7, the observed pattern coincides well with the one calculated by model (a). The interatomic distance and the X-ray diffraction data calculated by the Rietveld analysis are listed in tables 2 and 3. By the refinement, lattice parameters were determined to be a = 4 . 1 8 2 0 ( 6 ) A, b=4.1820(5) A, c=8.0889(9) A in the space group Pmmm. The crystal structure of the Ba2InCuO4.53 is shown in fig. 8. Interestingly, the a-axis length of the BalnO2.5 blocking layer is as long as 4.18 A, which is about 7% longer than the 3.92 A of the BaCuO2 layer. We guess that such a large misfit will break down the structure of Ba2InCuOy. The relaxation of the misfit is caused by the removal of the oxygen in the CuO2 plane. As listed in table 1 (a), about 74% of the O ( 4 ) and the O ( 5 ) sites in the CuO2 plane is removed. The vacancy will stretch the distance between the two neighboring Cu sites and match the blocking layer with a longer a-axis length. Actually, the in-plane Cu-

Rwp=

126

.% Kamt~e et al. /Structure ~d Bctfln( 'uO,

0 ( 4 ) and C u - O ( 5 ) bond distances are 2.091(0) A (table 2). The values are much longer than the observed Cu-O bond distances 1.92-1.96 ~ for hightemperature superconductors. Although we can sec the oxygen vacancy in the CuO chain of YBa2Cu30~. and the PbO-Cu-PbO block of Pb2Sr2 (Y, Ca )Cu30~ [ 19], their a-axis lengths lie in the standard range of the CuO2 layer (3.8-3.95 .A). Instead of the long aaxis length of the CuO2 layer for the In system, the bond distance between the Cu and the apex oxygen. O(3), is as short as 1.60 ,~. The short bond distance will relax the instability due to the existence of the oxygen vacancy in the CuO2 layer. Probably through structural hindrance, the shift of the 0 ( 3 ) toward the CuO2 planes causes the shift of the Ba ion toward the I n O 2 planes. The determined crystal structure is showed in fig. 7. The resistivity of Ba2InCuO4.53 was as large as 28.8 MO cm at room temperature. The high resistivity will be due to the lack of oxygen in the CuO2 layer. In order to fill the vacancy with oxygen, both the element substitution and the high pressure treatment are now carried out.

4. Conclusion In order to survey an unknown blocking layer which matches with the BaCuO>. layer, we examined the matching between the BaCuO2 and a variety of non-cuprate perovskite blocking layers. A new blocking layer with an a-axis length of 4.18/~, BalnO.~., was found. The blocking layer supplies an apical oxygen to the CuO2 layer and produces an oxygen vacancy in the CuO2 layer. From the HRTEM and the Rietveld analysis, it was found that the compound has a double perovskite structure (space group P m m m a=4.1820(6) A, b=4.1820(5) 3~, c=8.0889(9) .~). Resistivity measurements showed that Ba21nCuO4.~3 was insulating.

Acknowledgements We are grateful to Y. Syono and M. Kikuchi for the ICP measurement. A part of this work was sup-

portcd by the Nissan Foundation, the cooperation program of 1MR in Tohoku University, and the Grant of the Ministry of Education, Japan.

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