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Two new modulated structures in the (BiPb)2Sr2Ca2Cu3O10+δ superconductor
Physica C 203 ( 1992) 426-430 North-Holland
Two new modulated structures in the ( BiPb ) $3r2Ca2Cu30 I o + 6 superconductor X.C. Wu, T.S. Shi, Z.Z. ShengandT.G.
Chen
Shanghai Institute of Metallurgy, Chinese Academy of Sciences, Shanghai 200050, China Received
25 August
I992
s0 10+d is studied by TEM. Besides normal modulation with The modulation of the superconducting phase of (BiPb)&,Ca,Cu q, z 0.1 lb’, two new types of modulation with qz x & (a*+ 38’) and q3 x & (a*+ 2b’) are found in the post-annealed sample. These types of modulation are characterized by wave vectors located in the a*-b*-plane. The nature of these modulated structures is discussed in this report.
1. Introduction
2. Experimental
Among all high-T, superconductors, those of the Y-system and Bi-system provide the most hope for practical application, so their structures have been widely studied. One of the obvious characteristics of Bi-system superconductors is their modulated structure. The modulation is characterized by a wave vector, which is found to be located in the b*-c*-plane and is represented by q= pb* + yc*, here p= 0.2 1 and y varies for different n in Bi2SrZCan_ICu,02n+4+6 [ 1,2 1. The most pronounced modulation is found in Bi2SrZCu06+6 (2201 phase) with wave vector The modulation wave vector of a=0.2lb*+yc*. (2212 phase) and Bi2Sr2CaCuz08+6 BiZSr2Ca2Cu30,0+S (2223 phase) is q=O.21b*+c*, partial substitution of Pb for Bi stabilizes the 2223 phase, and both j3 and y reduce dramatically [ 3 1, so that q=O.l lb* [4], but all q remain in the b*-c*plane. The displacement of the atomic row along the u-axis ( [ 1001) in the modulated structure is synchronized and can be seen from HR images taken along [ 1001, consisting of alternative Bi-dense and Bi-deficient regions [ 5 1. In this report, we present evidence for two new types of modulation found in the post-annealed (BiPb)2SrzCazCu30,0+a compound with q located in the u*-b*-plane.
The superconducting sample was prepared by codecomposition of a nitrate mixture with Bi:Pb:Sr:Ca:Cu= 1.6:0.4:2:2:3 and subsequent calcination grinding, pressing and finally sintering at 855 “C, followed by slow furnace cooling [ 61. The sample is essentially single 2223 phase, as shown by XRD, and its T,(R= 0) equal to 105 K as measured by the four-probe resistivity method. Then, the sample was annealed in air at 600°C for 5 h and quenched in liquid nitrogen. In this state the T,(R=O) increases to 107.5 K. Disks of 3 mm diameter were cut from both the as-sintered and post-annealed samples, ground, dimpled and finally Ar+ ion-milled to electron transparency. The electron diffraction and HREM study was carried out using a JEM-4000EX electron microscope.
0921-4534/92/$05.00
0 1992 Elsevier Science Publishers
3. Results 3.1. The modulated structure of the as-sintered Pbdoped 2223 phase The basic structure of Pb-doped 2223 phase is orthorhombic with a~ bx0.54 nm and cz 3.70 nm. Its [ 1001 zone diffraction pattern is shown in fig. 1. In
B.V. All rights reserved.
X.C. Wu et al. /Two new modulatedstructures in the (BiPb)2SrZCaZCu3010+asuperconductor
427
3.2. New modulations in post-annealed Pb-doped 2223 phase
Fig. I. [ 1001 zone electron diffraction pattern of as-sintered Pbdoped Bi-2223 phase.
this figure, satellite reflections on both sides of the (02L) spots caused by modulation can be seen. The modulation is located in the ( 100) plane with wave vector qxO.1 lb* and period A.,~4.7 nm, the same as reported in ref. [ 2 1.
Besides the normal modulated structure reported above, two new types of modulated structure are found in the sample, post-annealed at 600°C for 5 h. The [ 3 10 1, [ 1301 zone diffraction patterns of the first modulated structure are shown in figs. 2 (a) and (b). In fig. 2(a), satellite spots on both sides of the main diffraction spots have been noticed along [ 130]*, but the satellite spots cannot be seen in fig. 2 (b). It indicates that this type of modulation is onedimensional and located in the (3 10) plane. The wave vector q2 determined from fig. 2(a) is about & (a.+3b’). The [ 2 lo] and [ 1201 zone diffraction patterns of the second modulated structure found in a different area of the post-annealed sample are shown in figs. 3(a) and (b). In fig. 3(a), the satellite reflections can again be noticed on both sides of the main diffraction spots (24L) along the [ 120]* direction and the satellite spots disappear in the [ 1201 zone diffraction pattern (fig. 3(b) ). Thus, the second type of modulation is also one-dimensional and located in the (210) plane with q2 x &(a*+26*).
Fig. 2. Electron diffraction patterns of the post-annealed Bi-2223 phase doped with Pb. (a) (5 lo] zone, (b) [ 1301 zone.
X.C. Wu et al. /Two new modulatedstructures
428
in the (BiPb)2Sr2Ca2Cu3010+a
superconductor
Fig. 3. Electron diffraction patterns of the post-annealed Bi-2223 phase doped with Pb. (a) [ 2 lo] zone, (b) [ 1201 zone.
Fig. 4. High-resolution image of as-sintered Bi-2223 phase doped with Pb viewed along [ LOO].
Fig. 5. HR image of post-annealed Pbdoped Bi-2223 phase viewedalong [310].
3.3. HR images
Figures 4, 5 and 6 are HR images of three types of modulation discussed above. Figure 4 is the [ 1001 zone HR image of the as-sintered Pb-doped 2223 phase. The horizontal parallel lines in fig. 4 are the (002) plane. The interplane distance d= 1.85 nm. The vertical black lines show modulation along [ 0 lo] with wavelength A, z 4.7 nm.
Figures 5 and 6 are HR images of modulated structures viewed along [ 3 10 ] and [ 2 10 ] in the postannealed Pb-doped 2223 phase. The modulation wavelength can be measured directly from these images to be about 5.1 nm and 5.8 nm. From the figures, the interplane spacing between (002) is determined to be 1.85 nm. The lack of modulated structure in the 90” rotation twin in fig. 6 serves as additional evidence for
429
XC. Wu et al. /Two new modulatedstructures in the (BiPb)3SrzCazCu3010+s superconductor
nm and cz 3.70 nm. So all of them are Bi-2223 compound doped with Pb. (2) The wave vectors of modulated structures in the Bi-system reported before are located in the b*c*-plane with a zero or very tiny component along the a*-axis. In these modulated structures there are no displacements along the u-axis and the atomic rows along the a-axis shift synchrously. However, in the newly discovered modulated structures in the post-annealed sample, their modulated vectors are distinguished by a significant component along the U.-axis. (3 ) It is generally accepted that the modulated structure in the Bi-system is correlated with extra interstitial oxygen atoms in (Bi0)2 [ 11. For the normal modulated structure in the Bi-system, the modulation vector is characterized by an essentially zero component along the a*-axis. The synchronous shift of the atomic row along the u-axis requires a synchronous introduction of extra interstitial oxygen atoms in the form of a row along the u-axis. For the modulated structures with q2 = $ the situation is (a*+36*) and q3 z & (a*+2b*), changed. It is suggested that the incorporation of extra interstitial oxygen atoms in the (BiO)* layer is no longer synchronous, but has some phase shift. As a result, the arrangement of extra interstitial oxygen atoms in the (BiO)z layer changes from a straight line along the u-axis to a ladder-like line as shown in
Fig. 6. HR image of post-annealed Ph-doped Bi-2223 phase viewed along [ 2 10 1, the upper part of the figure is a 90” rotation twin.
the one-dimensional ulated structure.
characteristic
of the new mod-
4. Discussions ( 1) The diffraction patterns and HR images presented above show that the basic structures of the three modulated phases are the same with ax bx 0.54
Ii001 a
0
T
0
0
I3lOJ
[ZIO] C
b
3
0
0
0
0
0
0
0
0
0
0
0
‘.
0 0
Bi atom x
Interstitial z: T
3
‘1
cl
.,
_’
oxygen
atom
‘33OC’ n
;
oc~oodooo
000000
b[OlOl Fig. 7. Top view of the arrangement of extra interstitial oxygen atoms in the ( BiO ) x layer in (a) normal (c) newly discovered modulated structures in post-annealed Ph-doped Bi-2223 phase.
modulated
structure,
(b ) and
430
X.C. Wu et al. /Two new modulated structures in the (BiPb)zSrzCa2Cu3010+d
fig. 7; therefore, it is suggested that the newly discovered modulated structures in the post-annealed Bi-2223 phase doped with Pb are formed as a result of the rearrangement of extra interstitial oxygen atoms during post-annealing.
superconductor
ladder-like line in the a-b-plane and it results in new types of modulated structures with modulation vectors q2 and q, located in the a*-b*-plane.
Acknowledgement
5. Conclusion ( 1) In post-annealed Pb-doped 2223 phase, three types of modulation are found by electron diffraction and HREM. Their wave vectors are q, z 0.1 lb*, q2 x 6 (a*+3b*), and q3 x & (a*+2b*). The first modulation is known already. The modulations with wave vectors q2 and q3 are newly discovered. (2) Differing from all the modulated structures reported before, the new types of modulation are characterized by a modulation wave vector located in the a*-b*-plane. (3) It is suggested that the arrangement of extra oxygen atoms in the ( Bi0)2 layer has changed during post-annealing from a row along the a-axis to a
This work was supported by the National Research and Development Center for Superconductivity of China.
References [ 1] H.W. Zandbergen, W.A. Groen, EC. Mijlhoff, G. Van Tendeloo and S. Amelinckx, Physica C 156 (1988) 325. [2]0.Eibl,PhysicaCl68(1990)215. [3] M. Takano, J. Tanaka, K. Oda, H. Kitaguchi, Y. Miura and Y. Ikeda, Jpn. J. Appl. Phys. 27 (1988) LlO41. [ 4 ] S. Ikeda, K. Aota, S. Horiuchi and A. Umezono, Jpn. J. Appl. Phys. 27 ( 1988) L2040. [ 51 Y. Matsui, H. Maeda, Y. Tanaka and S. Horiuchi, Jpn. J. Appl. Phys. 27 (1988) L361, L372. [6] C.J. Zhou, D.W. Li and J.G. Chen, Physica C 179 (1991) 369.
Two new modulated structures in the ( BiPb ) $3r2Ca2Cu30 I o + 6 superconductor X.C. Wu, T.S. Shi, Z.Z. ShengandT.G.
Chen
Shanghai Institute of Metallurgy, Chinese Academy of Sciences, Shanghai 200050, China Received
25 August
I992
s0 10+d is studied by TEM. Besides normal modulation with The modulation of the superconducting phase of (BiPb)&,Ca,Cu q, z 0.1 lb’, two new types of modulation with qz x & (a*+ 38’) and q3 x & (a*+ 2b’) are found in the post-annealed sample. These types of modulation are characterized by wave vectors located in the a*-b*-plane. The nature of these modulated structures is discussed in this report.
1. Introduction
2. Experimental
Among all high-T, superconductors, those of the Y-system and Bi-system provide the most hope for practical application, so their structures have been widely studied. One of the obvious characteristics of Bi-system superconductors is their modulated structure. The modulation is characterized by a wave vector, which is found to be located in the b*-c*-plane and is represented by q= pb* + yc*, here p= 0.2 1 and y varies for different n in Bi2SrZCan_ICu,02n+4+6 [ 1,2 1. The most pronounced modulation is found in Bi2SrZCu06+6 (2201 phase) with wave vector The modulation wave vector of a=0.2lb*+yc*. (2212 phase) and Bi2Sr2CaCuz08+6 BiZSr2Ca2Cu30,0+S (2223 phase) is q=O.21b*+c*, partial substitution of Pb for Bi stabilizes the 2223 phase, and both j3 and y reduce dramatically [ 3 1, so that q=O.l lb* [4], but all q remain in the b*-c*plane. The displacement of the atomic row along the u-axis ( [ 1001) in the modulated structure is synchronized and can be seen from HR images taken along [ 1001, consisting of alternative Bi-dense and Bi-deficient regions [ 5 1. In this report, we present evidence for two new types of modulation found in the post-annealed (BiPb)2SrzCazCu30,0+a compound with q located in the u*-b*-plane.
The superconducting sample was prepared by codecomposition of a nitrate mixture with Bi:Pb:Sr:Ca:Cu= 1.6:0.4:2:2:3 and subsequent calcination grinding, pressing and finally sintering at 855 “C, followed by slow furnace cooling [ 61. The sample is essentially single 2223 phase, as shown by XRD, and its T,(R= 0) equal to 105 K as measured by the four-probe resistivity method. Then, the sample was annealed in air at 600°C for 5 h and quenched in liquid nitrogen. In this state the T,(R=O) increases to 107.5 K. Disks of 3 mm diameter were cut from both the as-sintered and post-annealed samples, ground, dimpled and finally Ar+ ion-milled to electron transparency. The electron diffraction and HREM study was carried out using a JEM-4000EX electron microscope.
0921-4534/92/$05.00
0 1992 Elsevier Science Publishers
3. Results 3.1. The modulated structure of the as-sintered Pbdoped 2223 phase The basic structure of Pb-doped 2223 phase is orthorhombic with a~ bx0.54 nm and cz 3.70 nm. Its [ 1001 zone diffraction pattern is shown in fig. 1. In
B.V. All rights reserved.
X.C. Wu et al. /Two new modulatedstructures in the (BiPb)2SrZCaZCu3010+asuperconductor
427
3.2. New modulations in post-annealed Pb-doped 2223 phase
Fig. I. [ 1001 zone electron diffraction pattern of as-sintered Pbdoped Bi-2223 phase.
this figure, satellite reflections on both sides of the (02L) spots caused by modulation can be seen. The modulation is located in the ( 100) plane with wave vector qxO.1 lb* and period A.,~4.7 nm, the same as reported in ref. [ 2 1.
Besides the normal modulated structure reported above, two new types of modulated structure are found in the sample, post-annealed at 600°C for 5 h. The [ 3 10 1, [ 1301 zone diffraction patterns of the first modulated structure are shown in figs. 2 (a) and (b). In fig. 2(a), satellite spots on both sides of the main diffraction spots have been noticed along [ 130]*, but the satellite spots cannot be seen in fig. 2 (b). It indicates that this type of modulation is onedimensional and located in the (3 10) plane. The wave vector q2 determined from fig. 2(a) is about & (a.+3b’). The [ 2 lo] and [ 1201 zone diffraction patterns of the second modulated structure found in a different area of the post-annealed sample are shown in figs. 3(a) and (b). In fig. 3(a), the satellite reflections can again be noticed on both sides of the main diffraction spots (24L) along the [ 120]* direction and the satellite spots disappear in the [ 1201 zone diffraction pattern (fig. 3(b) ). Thus, the second type of modulation is also one-dimensional and located in the (210) plane with q2 x &(a*+26*).
Fig. 2. Electron diffraction patterns of the post-annealed Bi-2223 phase doped with Pb. (a) (5 lo] zone, (b) [ 1301 zone.
X.C. Wu et al. /Two new modulatedstructures
428
in the (BiPb)2Sr2Ca2Cu3010+a
superconductor
Fig. 3. Electron diffraction patterns of the post-annealed Bi-2223 phase doped with Pb. (a) [ 2 lo] zone, (b) [ 1201 zone.
Fig. 4. High-resolution image of as-sintered Bi-2223 phase doped with Pb viewed along [ LOO].
Fig. 5. HR image of post-annealed Pbdoped Bi-2223 phase viewedalong [310].
3.3. HR images
Figures 4, 5 and 6 are HR images of three types of modulation discussed above. Figure 4 is the [ 1001 zone HR image of the as-sintered Pb-doped 2223 phase. The horizontal parallel lines in fig. 4 are the (002) plane. The interplane distance d= 1.85 nm. The vertical black lines show modulation along [ 0 lo] with wavelength A, z 4.7 nm.
Figures 5 and 6 are HR images of modulated structures viewed along [ 3 10 ] and [ 2 10 ] in the postannealed Pb-doped 2223 phase. The modulation wavelength can be measured directly from these images to be about 5.1 nm and 5.8 nm. From the figures, the interplane spacing between (002) is determined to be 1.85 nm. The lack of modulated structure in the 90” rotation twin in fig. 6 serves as additional evidence for
429
XC. Wu et al. /Two new modulatedstructures in the (BiPb)3SrzCazCu3010+s superconductor
nm and cz 3.70 nm. So all of them are Bi-2223 compound doped with Pb. (2) The wave vectors of modulated structures in the Bi-system reported before are located in the b*c*-plane with a zero or very tiny component along the a*-axis. In these modulated structures there are no displacements along the u-axis and the atomic rows along the a-axis shift synchrously. However, in the newly discovered modulated structures in the post-annealed sample, their modulated vectors are distinguished by a significant component along the U.-axis. (3 ) It is generally accepted that the modulated structure in the Bi-system is correlated with extra interstitial oxygen atoms in (Bi0)2 [ 11. For the normal modulated structure in the Bi-system, the modulation vector is characterized by an essentially zero component along the a*-axis. The synchronous shift of the atomic row along the u-axis requires a synchronous introduction of extra interstitial oxygen atoms in the form of a row along the u-axis. For the modulated structures with q2 = $ the situation is (a*+36*) and q3 z & (a*+2b*), changed. It is suggested that the incorporation of extra interstitial oxygen atoms in the (BiO)* layer is no longer synchronous, but has some phase shift. As a result, the arrangement of extra interstitial oxygen atoms in the (BiO)z layer changes from a straight line along the u-axis to a ladder-like line as shown in
Fig. 6. HR image of post-annealed Ph-doped Bi-2223 phase viewed along [ 2 10 1, the upper part of the figure is a 90” rotation twin.
the one-dimensional ulated structure.
characteristic
of the new mod-
4. Discussions ( 1) The diffraction patterns and HR images presented above show that the basic structures of the three modulated phases are the same with ax bx 0.54
Ii001 a
0
T
0
0
I3lOJ
[ZIO] C
b
3
0
0
0
0
0
0
0
0
0
0
0
‘.
0 0
Bi atom x
Interstitial z: T
3
‘1
cl
.,
_’
oxygen
atom
‘33OC’ n
;
oc~oodooo
000000
b[OlOl Fig. 7. Top view of the arrangement of extra interstitial oxygen atoms in the ( BiO ) x layer in (a) normal (c) newly discovered modulated structures in post-annealed Ph-doped Bi-2223 phase.
modulated
structure,
(b ) and
430
X.C. Wu et al. /Two new modulated structures in the (BiPb)zSrzCa2Cu3010+d
fig. 7; therefore, it is suggested that the newly discovered modulated structures in the post-annealed Bi-2223 phase doped with Pb are formed as a result of the rearrangement of extra interstitial oxygen atoms during post-annealing.
superconductor
ladder-like line in the a-b-plane and it results in new types of modulated structures with modulation vectors q2 and q, located in the a*-b*-plane.
Acknowledgement
5. Conclusion ( 1) In post-annealed Pb-doped 2223 phase, three types of modulation are found by electron diffraction and HREM. Their wave vectors are q, z 0.1 lb*, q2 x 6 (a*+3b*), and q3 x & (a*+2b*). The first modulation is known already. The modulations with wave vectors q2 and q3 are newly discovered. (2) Differing from all the modulated structures reported before, the new types of modulation are characterized by a modulation wave vector located in the a*-b*-plane. (3) It is suggested that the arrangement of extra oxygen atoms in the ( Bi0)2 layer has changed during post-annealing from a row along the a-axis to a
This work was supported by the National Research and Development Center for Superconductivity of China.
References [ 1] H.W. Zandbergen, W.A. Groen, EC. Mijlhoff, G. Van Tendeloo and S. Amelinckx, Physica C 156 (1988) 325. [2]0.Eibl,PhysicaCl68(1990)215. [3] M. Takano, J. Tanaka, K. Oda, H. Kitaguchi, Y. Miura and Y. Ikeda, Jpn. J. Appl. Phys. 27 (1988) LlO41. [ 4 ] S. Ikeda, K. Aota, S. Horiuchi and A. Umezono, Jpn. J. Appl. Phys. 27 ( 1988) L2040. [ 51 Y. Matsui, H. Maeda, Y. Tanaka and S. Horiuchi, Jpn. J. Appl. Phys. 27 (1988) L361, L372. [6] C.J. Zhou, D.W. Li and J.G. Chen, Physica C 179 (1991) 369.