- Email: [email protected]
New cuprates with the 1222 structure: (Ce, M) Sr2(Gd, Ce)2 Cu2Oy(M = Zn,Ni)
PHYSICA ELSEVIER
Physica C 270 (1996)167-172
New cuprates with the 1222 structure: (Ce,M) Sr2(Gd,Ce)2CU2Oy( M = Zn,Ni) Luo Hongmei a, Chen Zuyao a,b, Li Rukang * ,a a Department of Applied Chemistry, University of Science and Technology of China, Hefei, Anhui 230026, China t, Structure Research Laboratory, University of Science and Technology of China, Hefei, Anhui 230026, China
Received 12 June 1996
Abstract
A new type of layered cuprate with the nominal composition (Ceo.sM0.5)Srz(Gd2_xCex)Cu2Oy (M = Zn,Ni) has been successfully synthesized and identified by X-ray diffraction analysis. The compounds have a tetragonal cell with the space group of I4/mmm. The lattice parameters of a = 3.8365(1) ,~, c = 29.2010(4) ~, for (Ce0.sZno.5)Sr2(Gdl.zCeo.8)CU2Oy and a = 3.8389(5) ,~, c = 29.0548(10) ,~ for the Ni analog were obtained from indexing the XRD patterns. By using the Rietveld refinement, the compounds were found possessing the same structure type as the common 1222 structure. Although complete CuO pyramidal planes also exist in the present compounds, the as-prepared samples are not superconducting above 15 K,
1. I n t r o d u c t i o n
Since the discovery of superconductivity in the so-called Cu-1222 compound, (Ln,Ce)2(Ba,Ln) 2Cu3Oj0 [1], several new layered cuprates with the 1222 structure have been reported, such as: (T1,Pb)1222 [2], (Pb,Cu)-1222 [3], MSr2(Ln,Ce)2Cu20.(M = Nb,Ta,Ti,Ga,A1,Co) [4-6] and (Bi,Cu)-1222 [7]. Their structures are all derived from the related i 212-type structure by replacing single (Ln,Ca) layer with a double (Ln,Ce)20 2 fluorite layer. According to our classification scheme [8], those compounds are the same but with different connecting layers which are the BaCuOy deficient perovskite, SrMO 3 c o m -
* Corresponding author.
plete perovskite and (Ba,Sr)(TI,Pb,Bi)O 2 rock salt layers, respectively, in the above compounds. Cerium is known to occupy the rock salt connecting layer in the 1212 type compound (T1,Ce)Sr 2CaCu207 [9], ( C e , M ) S r 2 ( Y , C a ) C u z O 7 ( M = Cd,Zn,Cu) [10] and also in one of the superconducting 1222 compounds [11], (Cu,Ce)Sra(Y,Ce)2CU2Oy. It is especially interesting that the latter compound, (Ce,Cu)-1222, possesses the unique structure where the Ce occupy both the separating fluorite layer and the connecting rock salt Sr(Ce,Cu)O 2 layer. In order to develop a new layered cuprate as a potential high-Tc superconductor, we have tried to replace the single (Y,Ca) layer in the above-mentioned (Ce,M)1212 compounds with the (Ln,Ce)O 2 fluorite layer, and succeeded in preparing a new series of 1222 cuprates, (Ce, M)Srz(Gd,Ce)~Cu 2Or ( M = Zn,Ni).
0921-4534/96/$15.00 Copyright © 1996 Elsevier Science B.V. All rights reserved PII S0921 -4534(96)00491- 1
168
H.M. Luo et al. / Physica C 270 (1996) 167-172
2. Experimental
annealed at 500°C for another 20 hours, finally followed by slow cooling to room temperature. Part of each pellet was further treated under high oxygen pressure in a sealed quartz tube (30 atm, 600°C, 20 hr). The X-ray powder diffraction (XRD) patterns were recorded with a Y-4Q X-ray diffractometer (Dandong Radiation Instrument Group Co.). The powder diffraction data for Rietveld analysis were collected in the range of 20-122 ° (20) at a step of 0.03 ° (20) and a counting time of 3 seconds with a Rigaku D m a x / r B diffractometer. The resistance of the samples was measured using the standard four-probe method down to 15 K in a commercial He circling
Samples with nominal compositions of (Ceo.5 Mo.5)Sr2(Gd 2-xCex) Cu 2Oy (M = Zn, Ni, 0.5 ~
2500
-. __ ~ ~
_.~__x=O.~5
2000
1500
......
I
i
ft..
x=0.8
1000 x=0.9
500
10
20
30
40
50
60
70
2e(CuKcO Fig. 1. X-ray powder diffraction patterns of (CeosZno.s)Sr2(Gd/_xCe~)Cu2Oy (the asterisks, triangles and a dot represent the impurity phases of CeO2, 1212 and an unknown phase, respectively).
H.M. Luo et al./Physica C 270 (1996) 167-172
Fig. 2. Schematic representation of the crystal structure of (Ce, M)Sr 2(Ln,Ce) 2Cu 2Oy-
refrigerator. The contacts were made by soldering fine Cu wires on indium pressed onto the sample surface. The temperatures were measured with a calibrated Rh-Fe resistance thermometer set close to the sample.
3. Results and discussion The X R D patterns o f the ( C e o s Z n o s ) S r 2(Gd2_xCe,)Cu2Oy samples are shown in Fig. 1. From the patterns, we found that the samples in the 0.6 < x < 0.9 range are primarily in a single phase.
169
The sample o f x = 0.5 contains the 1212 phase and that of x = 1.0 contains CeO 2 as impurities. For the samples containing Ni the single phase can also be obtained in the same region of 0.6 ~< x ~< 0.9 under similar preparation conditions. The XRD patterns of these phases are similar to that o f (Pb,Cu)-1222 samples and the diffraction peaks can be indexed based on a tetragonal body-center lattice with a space group I 4 / m m m . The lattice parameters obtained for (Ce%sM0.5)Sr2(Gd~.2Ce0o8)Cu2Oy are a = 3 . 8 3 6 5 ( 1 ) A, c = 29.2010(4) A for M = Zn, and a = 3.8389(5) A, c = 29.0548(10) A for M = Ni. The lattice parameo ters are also consistent with a = 3.840 A, c = 29.01 for ( P b , f u ) ( S r , G d ) 2 ( G d , C e ) 2 f u 2 0 z [12] and a = 3.820 A, c - - - 2 9 . 0 9 4 A for (Cu06Ce0.4)Sr 2(Yi.2Ce0.8)Cu20: [11]. Thus the basic structure of (Pb,Cu)-1222 should be also applicable to the present ( C e , M ) - I 2 2 2 compound. Fig. 2 shows a schematic representation of the crystallographic structure of (Ce,M)Sr2(Ln,Ce)2CU2Oy. The structure of ( C e , M ) - 1 2 2 2 can be described as a rock-salt-type block. The ( C e , M ) - O layer connects the apices of pyramidal CuO 5 and the bases of the pyramids are further separated by the double fluorite layer (Ln,Ce)O 2 . Structure refinement of the proposed model was performed by using the Rietveld method and the D B W S package [13]. A total of 38 parameters, including 5 polynomial background, 16 structural parameters and 17 other global parameters of zero point, scale factor, preferred orientation and peak shape parameters are refined. The pseudo-Voigt function was taken to describe the individual peak profile. At the beginning of refinement, the atomic
Table 1 Refined structural parameters for (Ceo.sZno.5)Sr2(Gdl.2Ceo.s)CU2Oy (space group 14/mmm and cell parameters a = 3.8365(1) ~,, c = 29.2010(4) ,~, Rwp = 8.44%, R B = 6.22%)
Atom
Site
x
y
z
n
B (,&2)
Ce/Zn Sr Gd/Ce Cu O( I) 0(2) 0(3) 0(4)
2a 4e 4e 4e 8h 4e 8g 4d
0 0 0 0 0.622(9) 0 0.5 0.5
0 0 0 0 0.622(9) 0 0 0
0 0.4163( 1) 0.2937( 1) 0.1443(2) 0 0.0659(6) 0.1507(6) 0.25
0.39(1)/0.61(1) 1 0.65/0.35 1 0.25 1 1 1
2.1(2) 1.3( 1) 0.35(6) 2.2(3) 1(1) 2.0(5) 2.2(3) 0.3
170
H.M. Luo et al./ Physica C 270 (1996) 167-172
positions from the other 1222 structure were taken as the starting points. During the progress of refinement, CeO 2 and 1212 impurities were found in the XRD pattern. Thus, CeO 2 was refined simultaneously with the 1222 main phase and the peaks at 20 = 32.44 (due to the 1212 phase) and 33.54 were excluded. The refinement went well except that the temperature factor of O1 turned out to be too large, and that of 0 4 went to meaningless negative values. The problems were solved by allowing the O1 to occupy a split position (813) and fixing the temperature factor of 0 4 (the selection of 0, 0.3 or - 0.5 of
Bo4
actually did not alter the agreement indices). The refinement converges to the following agreement indices: Rwp = 8.53%, S = 1.78, Dwd = 1.35 and R B = 6.75%. Table 1 lists the structural parameters obtained for (Ce0.sZn0.5)Sr2(Gdl.2Ce0.8)CU2Oy. Fig. 3 shows the Rietveld refinement patterns for (Ceo.sZn0.5)Sr2(Gdl.2Ce0.8)CU2Oy. Table 2 lists the selected inter-atomic distances between the metal and oxygen atoms calculated from the refined atomic parameters. Although the refinement led to good agreement indices, which seems to support the (Ce, M)-1222 model, we cannot fully exclude the
15000
10000 tat) e,0
5000 =-I
I
20
__
I
L
I
I
40
60
80
1O0
120
20(CuK~) Fig. 3. Observed (dotted) and calculated (solid line) X-ray diffraction pattern of (Ceo.hZno.5)Sr2(Gdj.2Ceo.8)CU2Oy. The diffraction peak marks and the difference plot are shown at the bottom of the figure.
H.M. Luo et a l . / Physica C 270 (1996) 167-172 Table 2 Selected bond lengths of (Ceo.sZno.5)Sr2(Gd LzCeo.s)Cu2Oy
30
Bond
r (~,)
Bond
r (~k)
25
Ce/Zn-O(I) Cu-O(2) Sr-O(1) Sr-O(3) Gd/Ce-O(4)
3.375(2.051) 2.289 2.574 2.740 2.304
Ce/Zn-O(2) Cu-O(3) Sr-O(2) Gd/Ce-O(3)
1.924 1.927 2.807 2.513
..~ 20
possibility that some Cu atoms occupy at the Ce sites in the rock salt connecting layer while Zn atoms substitute the CuO 5 pyramidal plane sites. The fact that we failed to prepare the Fe, Co analogs under similar conditions might show as a clue that such a hypothesis is unfavorable since Fe, Co ions are believed to preferably occupy the pyramidal plane sites [ 14]. Since complete two-dimensional CuO planes exist in the structure of the present compound as in common cuprate superconductors, (Ce,M)-1222 should be a superconductor if proper carrier concentration is achieved. However, all the as-prepared samples showed semiconductor-like behavior. Fig. 4 shows the temperature dependence of the normalized resistance for the (Ce05Zn05)Sr2(Gd2_xCex)CU2Oy samples prepared in flowing 0 2 gas. One can see that the x = 0.7 and 0.8 samples are narrow gap semi60 •
x=0.6
• •
x=0.7 x=0.8
--~
x=0.9
50 :
•
171
air
g
5
0
30arm O~"2 ~ ' l ' ' - ~ A,
t 50
i 100
J 150
i 200
I 250
300
Temperature(K)
Fig. 5. Temperature dependence of the normalized resistance for (Ceo.5Zno.5)Sr2(Gdl.3Ceo.7)Cu2Oy annealed under different con-
ditions.
conductors, and x = 0.6 and 0.9 samples are with a larger gap. The carriers of these compounds are holes as inferred from the in-plane C u - O bond length. In order to induce superconductivity, the samples were further treated under high 02 pressure. After such an annealing, the semiconducting activation energy of the sample for x = 0.7 dropped (Fig. 5). Taking into consideration that the (Cuo.6Ce0.4)SrE(Yi.2Ce0.8)Cu2Oy became a superconductor when treated under oxygen pressure of 2 GPa, we expect that the title compounds would become new superconductors under further heat treatment.
40
.~
r~
4. Conclusion
30
A new series of 1222-type Ce-based cuprates (Ce0. 5M0.5)Sr2(Gd2_xCex)Cu2Oy ( M - - Zn,Ni) has been prepared and characterized. The compounds crystallize in a similar structure to that of the (Pb,Cu)-1222 phase. We have not succeeded in making the samples superconducting yet.
20
10
I
T
50
100
- - T
. . . .
150
X
. . . .
200
T
. . . .
250
300
Temperature(K)
Fig. 4. Temperature dependence of the normalized resistance for (CeosZno.5)Sr2(Gd2_xCex)Cu20y samples prepared in flowing O 2 gas.
Acknowledgment This work was partially supported by the Fok Yingdong Education Foundation,
172
H.M. Luo et al./Physica C 270 (1996) 167-172
References [1] H. Sawa, K. Obara, J. Akimitsu, Y. Matusi and S. Horiuchi, J. Phys. Soc. Jpn. 58 (1989) 2252. [2] C. Martin, D. Bourgault, M. Hervieu, C. Michel, J. Provost and B. Raveau, Mod. Phys. Lett. B 3 (1989) 993. T. Mochiku, T. Nagashima, Y. Saito, M. Watahiki, H. Asano and Y. Fukai, Jpn. J. Appl. Phys. 29 (1990) L588. [3] S. Adachi, O. Inoue, S. Kawashima, H. Adachi, Y. Ichikawa, K. Setsune and K. Wasa Physica C 168 (1990) 1. T. Maeda, K. Sakuyama, S. Koriyama, A. lchinose, H. Yamauchi and S. Tanaka, Physica C 169 (1990) 133. [4] Li Rukang, Zhu Yingjie, Qian Yitai and Chen Zuyao, Physica C 176 (1991) 19. Li Rukang, Zhu Yingjie, Xu Cheng, Chen Zuyao, Qian Yitai and Fang Chenggao, J. Solid State Chem. 94 (1991) 206. [5] Li Rukang, R.K. Kremer and J. Marier, Physica C 200 (1992) 344.
[6] R.J. Cava, H.W. Zandbergen, J.J. Krajewski, W.F. Peck, Jr, B. Hessen, R.B. Van Dover and S.W. Cheong, Physica C 198 (1992) 27. [7] A. Schilling, J.D. Guo, M. Cantoni, F. Hulliger, B. Xue and H.R. Ott, Mater. Lett. 15 (1992) 141. [8] Li Rukang, Appl. Phys. Commun. 11 (1992) 295. [9] Z. lqbal, B.L. Ramakrishna and J.C. Barry, Physica C 169 (199O) 396. [10] T.P. Beales, C. Dineen, S.R. Hall, M.R. Harrison and J.M. Parberry, Physica C 207 (1993) 1. [11] A. Ono and S. Horiuchi, Physica C 216 (1993) 165. [12] N. Sakai, T. Maeda, H. Yamauchi and S. Tanaka, Physica C 212 (1993) 75. [13] R.A. Young, A. Sakthivel, T.S. Moss and C.O. Paiva-Santos, J. Appl. Cryst. 28 (1995) 366. [I 4] L. Er-Rakho, C. Michel, Ph. Lacorre and B. Raveau, J. Solid State Chem. 73 (1988) 531. L. Barbey, N. Nguyen, V. Caignaert, M. Hervieu and B. Raveau, Mater. Res. Bull. 27 (1992) 295.
Physica C 270 (1996)167-172
New cuprates with the 1222 structure: (Ce,M) Sr2(Gd,Ce)2CU2Oy( M = Zn,Ni) Luo Hongmei a, Chen Zuyao a,b, Li Rukang * ,a a Department of Applied Chemistry, University of Science and Technology of China, Hefei, Anhui 230026, China t, Structure Research Laboratory, University of Science and Technology of China, Hefei, Anhui 230026, China
Received 12 June 1996
Abstract
A new type of layered cuprate with the nominal composition (Ceo.sM0.5)Srz(Gd2_xCex)Cu2Oy (M = Zn,Ni) has been successfully synthesized and identified by X-ray diffraction analysis. The compounds have a tetragonal cell with the space group of I4/mmm. The lattice parameters of a = 3.8365(1) ,~, c = 29.2010(4) ~, for (Ce0.sZno.5)Sr2(Gdl.zCeo.8)CU2Oy and a = 3.8389(5) ,~, c = 29.0548(10) ,~ for the Ni analog were obtained from indexing the XRD patterns. By using the Rietveld refinement, the compounds were found possessing the same structure type as the common 1222 structure. Although complete CuO pyramidal planes also exist in the present compounds, the as-prepared samples are not superconducting above 15 K,
1. I n t r o d u c t i o n
Since the discovery of superconductivity in the so-called Cu-1222 compound, (Ln,Ce)2(Ba,Ln) 2Cu3Oj0 [1], several new layered cuprates with the 1222 structure have been reported, such as: (T1,Pb)1222 [2], (Pb,Cu)-1222 [3], MSr2(Ln,Ce)2Cu20.(M = Nb,Ta,Ti,Ga,A1,Co) [4-6] and (Bi,Cu)-1222 [7]. Their structures are all derived from the related i 212-type structure by replacing single (Ln,Ca) layer with a double (Ln,Ce)20 2 fluorite layer. According to our classification scheme [8], those compounds are the same but with different connecting layers which are the BaCuOy deficient perovskite, SrMO 3 c o m -
* Corresponding author.
plete perovskite and (Ba,Sr)(TI,Pb,Bi)O 2 rock salt layers, respectively, in the above compounds. Cerium is known to occupy the rock salt connecting layer in the 1212 type compound (T1,Ce)Sr 2CaCu207 [9], ( C e , M ) S r 2 ( Y , C a ) C u z O 7 ( M = Cd,Zn,Cu) [10] and also in one of the superconducting 1222 compounds [11], (Cu,Ce)Sra(Y,Ce)2CU2Oy. It is especially interesting that the latter compound, (Ce,Cu)-1222, possesses the unique structure where the Ce occupy both the separating fluorite layer and the connecting rock salt Sr(Ce,Cu)O 2 layer. In order to develop a new layered cuprate as a potential high-Tc superconductor, we have tried to replace the single (Y,Ca) layer in the above-mentioned (Ce,M)1212 compounds with the (Ln,Ce)O 2 fluorite layer, and succeeded in preparing a new series of 1222 cuprates, (Ce, M)Srz(Gd,Ce)~Cu 2Or ( M = Zn,Ni).
0921-4534/96/$15.00 Copyright © 1996 Elsevier Science B.V. All rights reserved PII S0921 -4534(96)00491- 1
168
H.M. Luo et al. / Physica C 270 (1996) 167-172
2. Experimental
annealed at 500°C for another 20 hours, finally followed by slow cooling to room temperature. Part of each pellet was further treated under high oxygen pressure in a sealed quartz tube (30 atm, 600°C, 20 hr). The X-ray powder diffraction (XRD) patterns were recorded with a Y-4Q X-ray diffractometer (Dandong Radiation Instrument Group Co.). The powder diffraction data for Rietveld analysis were collected in the range of 20-122 ° (20) at a step of 0.03 ° (20) and a counting time of 3 seconds with a Rigaku D m a x / r B diffractometer. The resistance of the samples was measured using the standard four-probe method down to 15 K in a commercial He circling
Samples with nominal compositions of (Ceo.5 Mo.5)Sr2(Gd 2-xCex) Cu 2Oy (M = Zn, Ni, 0.5 ~
2500
-. __ ~ ~
_.~__x=O.~5
2000
1500
......
I
i
ft..
x=0.8
1000 x=0.9
500
10
20
30
40
50
60
70
2e(CuKcO Fig. 1. X-ray powder diffraction patterns of (CeosZno.s)Sr2(Gd/_xCe~)Cu2Oy (the asterisks, triangles and a dot represent the impurity phases of CeO2, 1212 and an unknown phase, respectively).
H.M. Luo et al./Physica C 270 (1996) 167-172
Fig. 2. Schematic representation of the crystal structure of (Ce, M)Sr 2(Ln,Ce) 2Cu 2Oy-
refrigerator. The contacts were made by soldering fine Cu wires on indium pressed onto the sample surface. The temperatures were measured with a calibrated Rh-Fe resistance thermometer set close to the sample.
3. Results and discussion The X R D patterns o f the ( C e o s Z n o s ) S r 2(Gd2_xCe,)Cu2Oy samples are shown in Fig. 1. From the patterns, we found that the samples in the 0.6 < x < 0.9 range are primarily in a single phase.
169
The sample o f x = 0.5 contains the 1212 phase and that of x = 1.0 contains CeO 2 as impurities. For the samples containing Ni the single phase can also be obtained in the same region of 0.6 ~< x ~< 0.9 under similar preparation conditions. The XRD patterns of these phases are similar to that o f (Pb,Cu)-1222 samples and the diffraction peaks can be indexed based on a tetragonal body-center lattice with a space group I 4 / m m m . The lattice parameters obtained for (Ce%sM0.5)Sr2(Gd~.2Ce0o8)Cu2Oy are a = 3 . 8 3 6 5 ( 1 ) A, c = 29.2010(4) A for M = Zn, and a = 3.8389(5) A, c = 29.0548(10) A for M = Ni. The lattice parameo ters are also consistent with a = 3.840 A, c = 29.01 for ( P b , f u ) ( S r , G d ) 2 ( G d , C e ) 2 f u 2 0 z [12] and a = 3.820 A, c - - - 2 9 . 0 9 4 A for (Cu06Ce0.4)Sr 2(Yi.2Ce0.8)Cu20: [11]. Thus the basic structure of (Pb,Cu)-1222 should be also applicable to the present ( C e , M ) - I 2 2 2 compound. Fig. 2 shows a schematic representation of the crystallographic structure of (Ce,M)Sr2(Ln,Ce)2CU2Oy. The structure of ( C e , M ) - 1 2 2 2 can be described as a rock-salt-type block. The ( C e , M ) - O layer connects the apices of pyramidal CuO 5 and the bases of the pyramids are further separated by the double fluorite layer (Ln,Ce)O 2 . Structure refinement of the proposed model was performed by using the Rietveld method and the D B W S package [13]. A total of 38 parameters, including 5 polynomial background, 16 structural parameters and 17 other global parameters of zero point, scale factor, preferred orientation and peak shape parameters are refined. The pseudo-Voigt function was taken to describe the individual peak profile. At the beginning of refinement, the atomic
Table 1 Refined structural parameters for (Ceo.sZno.5)Sr2(Gdl.2Ceo.s)CU2Oy (space group 14/mmm and cell parameters a = 3.8365(1) ~,, c = 29.2010(4) ,~, Rwp = 8.44%, R B = 6.22%)
Atom
Site
x
y
z
n
B (,&2)
Ce/Zn Sr Gd/Ce Cu O( I) 0(2) 0(3) 0(4)
2a 4e 4e 4e 8h 4e 8g 4d
0 0 0 0 0.622(9) 0 0.5 0.5
0 0 0 0 0.622(9) 0 0 0
0 0.4163( 1) 0.2937( 1) 0.1443(2) 0 0.0659(6) 0.1507(6) 0.25
0.39(1)/0.61(1) 1 0.65/0.35 1 0.25 1 1 1
2.1(2) 1.3( 1) 0.35(6) 2.2(3) 1(1) 2.0(5) 2.2(3) 0.3
170
H.M. Luo et al./ Physica C 270 (1996) 167-172
positions from the other 1222 structure were taken as the starting points. During the progress of refinement, CeO 2 and 1212 impurities were found in the XRD pattern. Thus, CeO 2 was refined simultaneously with the 1222 main phase and the peaks at 20 = 32.44 (due to the 1212 phase) and 33.54 were excluded. The refinement went well except that the temperature factor of O1 turned out to be too large, and that of 0 4 went to meaningless negative values. The problems were solved by allowing the O1 to occupy a split position (813) and fixing the temperature factor of 0 4 (the selection of 0, 0.3 or - 0.5 of
Bo4
actually did not alter the agreement indices). The refinement converges to the following agreement indices: Rwp = 8.53%, S = 1.78, Dwd = 1.35 and R B = 6.75%. Table 1 lists the structural parameters obtained for (Ce0.sZn0.5)Sr2(Gdl.2Ce0.8)CU2Oy. Fig. 3 shows the Rietveld refinement patterns for (Ceo.sZn0.5)Sr2(Gdl.2Ce0.8)CU2Oy. Table 2 lists the selected inter-atomic distances between the metal and oxygen atoms calculated from the refined atomic parameters. Although the refinement led to good agreement indices, which seems to support the (Ce, M)-1222 model, we cannot fully exclude the
15000
10000 tat) e,0
5000 =-I
I
20
__
I
L
I
I
40
60
80
1O0
120
20(CuK~) Fig. 3. Observed (dotted) and calculated (solid line) X-ray diffraction pattern of (Ceo.hZno.5)Sr2(Gdj.2Ceo.8)CU2Oy. The diffraction peak marks and the difference plot are shown at the bottom of the figure.
H.M. Luo et a l . / Physica C 270 (1996) 167-172 Table 2 Selected bond lengths of (Ceo.sZno.5)Sr2(Gd LzCeo.s)Cu2Oy
30
Bond
r (~,)
Bond
r (~k)
25
Ce/Zn-O(I) Cu-O(2) Sr-O(1) Sr-O(3) Gd/Ce-O(4)
3.375(2.051) 2.289 2.574 2.740 2.304
Ce/Zn-O(2) Cu-O(3) Sr-O(2) Gd/Ce-O(3)
1.924 1.927 2.807 2.513
..~ 20
possibility that some Cu atoms occupy at the Ce sites in the rock salt connecting layer while Zn atoms substitute the CuO 5 pyramidal plane sites. The fact that we failed to prepare the Fe, Co analogs under similar conditions might show as a clue that such a hypothesis is unfavorable since Fe, Co ions are believed to preferably occupy the pyramidal plane sites [ 14]. Since complete two-dimensional CuO planes exist in the structure of the present compound as in common cuprate superconductors, (Ce,M)-1222 should be a superconductor if proper carrier concentration is achieved. However, all the as-prepared samples showed semiconductor-like behavior. Fig. 4 shows the temperature dependence of the normalized resistance for the (Ce05Zn05)Sr2(Gd2_xCex)CU2Oy samples prepared in flowing 0 2 gas. One can see that the x = 0.7 and 0.8 samples are narrow gap semi60 •
x=0.6
• •
x=0.7 x=0.8
--~
x=0.9
50 :
•
171
air
g
5
0
30arm O~"2 ~ ' l ' ' - ~ A,
t 50
i 100
J 150
i 200
I 250
300
Temperature(K)
Fig. 5. Temperature dependence of the normalized resistance for (Ceo.5Zno.5)Sr2(Gdl.3Ceo.7)Cu2Oy annealed under different con-
ditions.
conductors, and x = 0.6 and 0.9 samples are with a larger gap. The carriers of these compounds are holes as inferred from the in-plane C u - O bond length. In order to induce superconductivity, the samples were further treated under high 02 pressure. After such an annealing, the semiconducting activation energy of the sample for x = 0.7 dropped (Fig. 5). Taking into consideration that the (Cuo.6Ce0.4)SrE(Yi.2Ce0.8)Cu2Oy became a superconductor when treated under oxygen pressure of 2 GPa, we expect that the title compounds would become new superconductors under further heat treatment.
40
.~
r~
4. Conclusion
30
A new series of 1222-type Ce-based cuprates (Ce0. 5M0.5)Sr2(Gd2_xCex)Cu2Oy ( M - - Zn,Ni) has been prepared and characterized. The compounds crystallize in a similar structure to that of the (Pb,Cu)-1222 phase. We have not succeeded in making the samples superconducting yet.
20
10
I
T
50
100
- - T
. . . .
150
X
. . . .
200
T
. . . .
250
300
Temperature(K)
Fig. 4. Temperature dependence of the normalized resistance for (CeosZno.5)Sr2(Gd2_xCex)Cu20y samples prepared in flowing O 2 gas.
Acknowledgment This work was partially supported by the Fok Yingdong Education Foundation,
172
H.M. Luo et al./Physica C 270 (1996) 167-172
References [1] H. Sawa, K. Obara, J. Akimitsu, Y. Matusi and S. Horiuchi, J. Phys. Soc. Jpn. 58 (1989) 2252. [2] C. Martin, D. Bourgault, M. Hervieu, C. Michel, J. Provost and B. Raveau, Mod. Phys. Lett. B 3 (1989) 993. T. Mochiku, T. Nagashima, Y. Saito, M. Watahiki, H. Asano and Y. Fukai, Jpn. J. Appl. Phys. 29 (1990) L588. [3] S. Adachi, O. Inoue, S. Kawashima, H. Adachi, Y. Ichikawa, K. Setsune and K. Wasa Physica C 168 (1990) 1. T. Maeda, K. Sakuyama, S. Koriyama, A. lchinose, H. Yamauchi and S. Tanaka, Physica C 169 (1990) 133. [4] Li Rukang, Zhu Yingjie, Qian Yitai and Chen Zuyao, Physica C 176 (1991) 19. Li Rukang, Zhu Yingjie, Xu Cheng, Chen Zuyao, Qian Yitai and Fang Chenggao, J. Solid State Chem. 94 (1991) 206. [5] Li Rukang, R.K. Kremer and J. Marier, Physica C 200 (1992) 344.
[6] R.J. Cava, H.W. Zandbergen, J.J. Krajewski, W.F. Peck, Jr, B. Hessen, R.B. Van Dover and S.W. Cheong, Physica C 198 (1992) 27. [7] A. Schilling, J.D. Guo, M. Cantoni, F. Hulliger, B. Xue and H.R. Ott, Mater. Lett. 15 (1992) 141. [8] Li Rukang, Appl. Phys. Commun. 11 (1992) 295. [9] Z. lqbal, B.L. Ramakrishna and J.C. Barry, Physica C 169 (199O) 396. [10] T.P. Beales, C. Dineen, S.R. Hall, M.R. Harrison and J.M. Parberry, Physica C 207 (1993) 1. [11] A. Ono and S. Horiuchi, Physica C 216 (1993) 165. [12] N. Sakai, T. Maeda, H. Yamauchi and S. Tanaka, Physica C 212 (1993) 75. [13] R.A. Young, A. Sakthivel, T.S. Moss and C.O. Paiva-Santos, J. Appl. Cryst. 28 (1995) 366. [I 4] L. Er-Rakho, C. Michel, Ph. Lacorre and B. Raveau, J. Solid State Chem. 73 (1988) 531. L. Barbey, N. Nguyen, V. Caignaert, M. Hervieu and B. Raveau, Mater. Res. Bull. 27 (1992) 295.