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Growth and characterisation of Bi2Sr2Ca1Cu2Oy by the floating zone method
Materials
Chemistry
and Physics,
31 (1992)
281
281-284
Short Communication Growth and characterisation of Bi2Sr,CalCu20, by the floating zone method P. Murugakoothan, R. Jayavel, C. R. Venkateswara Rao, C. Subramanian and P. Ramasamy Crystal
Growth
(Received
Centre, Anna
September
University,
30, 1991; accepted
Madras-25
November
(India)
11, 1991)
Abstract The floating Zone Melting (FZM) technique using the immersed strip heater arrangement was adopted to grow BizSr,CaICuzOy crystals. High quality single crystals have been obtained from the grown boule. The crystals were investigated with an optical microscope to understand the growth mechanism. The growth direction is perpendicular to the (001) plane. The crystals have an orthorhombic structure with cell parameters a =5.40 A, b =5.44 8, and c=30.74 A. The composition of the grown crystal is Bi,.,Sr,,,Ca,.,,CuzOs,,. Superconducting transition of crystals occur at 82 K.
Introduction
Since the discovery of high T, superconductivity in Bi-cuprate [l] there has been intense activity concentrated on growing superconducting Bi-SrCa-Cu-0 single crystals. The flux technique is normally used to grow the crystals of these incongruently melting materials [2-51. But in all systems so far known for high T, superconductivity, one has encountered problems during crystal growth due to the reactivity of the fluxes. A very long growth process time due to a low growth rate leads to the contamination of the melt. The next difficulty arises due to the creeping of the melt along the walls of the crucible. This changes the melt composition during the growth process. All these problems, especially the contamination, make a crucible free method necessary. The floating zone melting technique [6, 71 has proved to be a very promising method of preparing the samples of highly textured microstructures with superconducting grains elongated and well aligned in the ab plane. A textured microstructure in a superconductor has been found to improve the critical current density enormously [S, 91.
0254-0584/92/$5.00
In this paper we report on the Immersed Heater Floating Zone Melting (IHFZM) [lo, 111 preparation of textured superconducting Bi-Sr-Ca-Cu-0 crystals grown in ambient air. So far no attempt has been made to grow these crystals by the IHFZM technique. This is a more suitable technique for growing highly textured Bi-Sr-Ca-Cu-0 with large crystals. The grown crystals were examined by Optical Microscopy, Powder X-ray diffraction, Electron Probe Micro Analyzer (EPMA) and DC resistivity measurements.
Experimental
The polycrystalline rods of composition Bi2Sr2CalCu20,, were prepared as feed material using highly pure Bi203, SrCO,, CaCO, and CuO. Appropriate amounts of starting materials were taken and mixed together in triple distilled water. The resulting homogenized slurry was dried and calcined at 800 “C for 4 hours. Samples were again milled in isopropyl alcohol, dried and charged into the steel die. The ceramic rods of 1 cm diameter and 2 cm length were prepared by applying a pressure of 5 tons/cm’. The prepared rods were sintered at 790 “C in flowing oxygen for 2 hours. The crystal growth apparatus is an immersed heater type floating zone furnace described elsewhere in detail [12]. The platinum strip was used as a heating source. Holes of diameter 0.5 to 1 mm were made at the central part of the strip to form a circular configuration, which was found to give a steady temperature at the growth zone [13]. The holes in the strip connect the molten zones on both sides of the strip and provide the facility for material transport from the feed zone to growth zone. The seed crystal was prepared from a crystalline boule obtained by zone melting the polycrystalline rod. Single crystals of Bi&,CarCu,O, were grown by using the crystalline boule as seed and the polycrystalline rod as feed. In the growth process, the platinum strip was maintained just above the melting point of the material. The seed rod rotation of 5 r-pm was used for thorough stirring of the melt. The automatic vertical downward pull was started at a rate of 1 mm/h when an appropriate interface was formed. After the growth was over, the temperature of
0
1992 - Elsevier
Sequoia. All rights reserved
282
the platinum strip was kept constant for 5 hours without pulling. Then the temperature was reduced gradually to 300 “C and quenched to room temperature. Finally the crystal boule was annealed at 800 “C in air for 48 hours. The preferred orientation of the elongated superconducting grain in the grown boule was confirmed by a Leitz optical microscope. The X-ray powder diffraction studies were made at room temperature with CuKcv radiation to confirm the phase of the grown crystal. The composition of the grown crystals were analyzed by an electron probe micro analyzer on the surface perpendicular to the growth axis. The DC four probe technique was used to measure the resistance of the sample with an input excitation current of 10 mA. The contacts were made, using silver paint, on the surface perpendicular to the growth axis of the crystal boule.
Results
Fig. 2. Optical micrograph of a cleaved surface along the growth axis (arrow indicates the growth axis).
and discussion
The as grown boule with seed is shown in Fig. 1. The surface of the grown boule along the growth axis shows a highly textured surface morphology (Fig. 2). The crystals are prolonged along the ingot axis and the ab plane is perpendicular to the melt surface. Figure 3 shows the optical micrograph of the aggregation of platelet crystals aligned parallel to each other along the pulling direction. The single crystals were picked up from the crystal boule by cleaving along the growth axis. The phase of the grown crystal and the cell constants were determined from the powder X-ray diffractogram of the crystal boule (Fig. 4). It reveals that the grown crystal is a single phase
Fig. 1. The photograph
of a grown crystal boule with seed.
Fig. 3. Optical micrograph showing the aggregation of crystals packed along the growth axis (arrow indicates the growth axis).
(2212) with traces of B&O3 and CuO impurity peaks and 2223 phase. The observed impurity peaks may be due to the precipitation of a very small quantity of B&O3 and CuO during stable growth. This is due to the large temperature gradient experienced by the molten material at the growth zone. The presence of the 2223 phase peak may be due to the syntactic growth of various phases. The cell constants were determined as a =5.40 A, b =5.44 8, and c=30.74 A, by the least squares method. The EPMA observation (Fig. 5) of the sample shows that the zone melted sample is in the Bi 2212 phase. The chemical composition of the grown sample is close to Bi2.04Srl.8Cal.16CuzO~+~Resistive transition of the Biz.04SrI.8Ca&uz08+y crystal as a function of temperature in the annealed state is shown in Fig. 6. The crystalline ingot exhibits a T, onset at 90 K and zero resistance was measured at 82 K. The detailed field and frequency depen-
283
2223
l
z 0 0
60
55
M
45
LO
DIFFRACTION
Fig. 4. Powder X-ray diffractogram
35
ANGLE
2B
30
.
cue
.
El1203
25
20
(degrees)
of the grown crystal boule.
d Y
:
0 1 J
6 m
i
oos-
0.00
I
I
L
1
Fig. 6. Resistive transition a function of temperature.
ENERGY
Fig. 5. EPMA arbitrary).
1
6
spectrum
8
10
12
I KeV)
of Bi,,,Sr,,,Ca,.,,Cu,O,,,
(peaks
are
dence of the ac susceptibility and the current density of the textured high density samples will be reported later. Conclusion
88
116 TEMPERATURE
VJ”’
2
I 60
IL1
172 (Kl
2c
A
of Bi,,,Sr,,,Ca,.,,Cu,O,,,
crystal as
nique. This method presents some advantages over the conventional floating zone technique. Unlike in the conventional floating zone process the melt zone is usually very stable with precise control over the planar growth front and also the growth initiation with a seed crystal is particularly easy. The zone melted samples show a highly textured microstructure with crystals extending along the growth axis. Their X-ray diffraction pattern confirms their orthorhombic structure. The chemical composition of the grown crystal is Bi,,Sr&aI.&u~08 +,, The resistivity measurements on the grown crystals show their normal state resistivity to be linear with temperature and have zero resistance at 82 K.
284
References 1 H. Maeda, Y. Tanaka, M. Fukutomi and T. Asano, Ipn. J, A&. Phys., 27 (1989) L209. 2 J. M. Tar-axon, Y. Le Page, P. Barboux, B. G. Bagley, L. H. Greene, W. R. Mckinnon, G. W. Hull, M. Giroud and D. H. Huang, Phys. Rev. B, 37 (1988) 9382. 3 P. Sureshkumar, C. Subramaian and P. Ramasamy, Mod. Phys. Lett. B, 3 (1989) 1417. 4 H. Takagi, H. Eisaki, S. Uchida, A. Maeda, S. Tajima, K. Uchinokura and S. Tanaka, Nature, 332 (1988) 236. 5 L. F. Schneemeyer, R. B. Van Dover, S. H. Glarum, S. A. Sunshine, R. M. Fleming, B. Batlogg, T. Siegrist, J. M, Marshall, J. V. Waszczak and L. W. Rupp, Nature, 332 (1988) 422.
6 M. J. Cima, X. P. Jiang, H. M. Chow, J. S. Haggerty, M. C. Flemings, H. D. Brody, R. A. Laudise and D. W. Johnson, J. Mat. Res., 5 (1990) 1834. 7 S. Takekawa, H. Nozaki, A. Umezono, K. Kosuda and M. Kobayashi, J. Crystal Growth, 92 (1988) 687. 8 K. Tsushima, Prog. High Temp. Superconductivity, 24 (1989) 10. 9 K. Salama, V. Selvamanickam, L. Gao and K. Sun, A&. Phys. Len., 54 (1989) 2352. 10 J. J. Brissot and C. Belin, J. CIYS~.Growth, 8 (1971) 213. 11 P. R. Swinehart, J. Cryst. Growth, 26 (1974) 317. 12 M. Palaniswamy, F. D. Gnanam, P. Ramasamy and G. S. Laddha, Cvsi. Res. Technol., 17 (1982) 911. 13 R. Gopalakrishnan, D. Arivu Oh and P. Ramasamy, Cryst. Res. Technol., (in press).
Chemistry
and Physics,
31 (1992)
281
281-284
Short Communication Growth and characterisation of Bi2Sr,CalCu20, by the floating zone method P. Murugakoothan, R. Jayavel, C. R. Venkateswara Rao, C. Subramanian and P. Ramasamy Crystal
Growth
(Received
Centre, Anna
September
University,
30, 1991; accepted
Madras-25
November
(India)
11, 1991)
Abstract The floating Zone Melting (FZM) technique using the immersed strip heater arrangement was adopted to grow BizSr,CaICuzOy crystals. High quality single crystals have been obtained from the grown boule. The crystals were investigated with an optical microscope to understand the growth mechanism. The growth direction is perpendicular to the (001) plane. The crystals have an orthorhombic structure with cell parameters a =5.40 A, b =5.44 8, and c=30.74 A. The composition of the grown crystal is Bi,.,Sr,,,Ca,.,,CuzOs,,. Superconducting transition of crystals occur at 82 K.
Introduction
Since the discovery of high T, superconductivity in Bi-cuprate [l] there has been intense activity concentrated on growing superconducting Bi-SrCa-Cu-0 single crystals. The flux technique is normally used to grow the crystals of these incongruently melting materials [2-51. But in all systems so far known for high T, superconductivity, one has encountered problems during crystal growth due to the reactivity of the fluxes. A very long growth process time due to a low growth rate leads to the contamination of the melt. The next difficulty arises due to the creeping of the melt along the walls of the crucible. This changes the melt composition during the growth process. All these problems, especially the contamination, make a crucible free method necessary. The floating zone melting technique [6, 71 has proved to be a very promising method of preparing the samples of highly textured microstructures with superconducting grains elongated and well aligned in the ab plane. A textured microstructure in a superconductor has been found to improve the critical current density enormously [S, 91.
0254-0584/92/$5.00
In this paper we report on the Immersed Heater Floating Zone Melting (IHFZM) [lo, 111 preparation of textured superconducting Bi-Sr-Ca-Cu-0 crystals grown in ambient air. So far no attempt has been made to grow these crystals by the IHFZM technique. This is a more suitable technique for growing highly textured Bi-Sr-Ca-Cu-0 with large crystals. The grown crystals were examined by Optical Microscopy, Powder X-ray diffraction, Electron Probe Micro Analyzer (EPMA) and DC resistivity measurements.
Experimental
The polycrystalline rods of composition Bi2Sr2CalCu20,, were prepared as feed material using highly pure Bi203, SrCO,, CaCO, and CuO. Appropriate amounts of starting materials were taken and mixed together in triple distilled water. The resulting homogenized slurry was dried and calcined at 800 “C for 4 hours. Samples were again milled in isopropyl alcohol, dried and charged into the steel die. The ceramic rods of 1 cm diameter and 2 cm length were prepared by applying a pressure of 5 tons/cm’. The prepared rods were sintered at 790 “C in flowing oxygen for 2 hours. The crystal growth apparatus is an immersed heater type floating zone furnace described elsewhere in detail [12]. The platinum strip was used as a heating source. Holes of diameter 0.5 to 1 mm were made at the central part of the strip to form a circular configuration, which was found to give a steady temperature at the growth zone [13]. The holes in the strip connect the molten zones on both sides of the strip and provide the facility for material transport from the feed zone to growth zone. The seed crystal was prepared from a crystalline boule obtained by zone melting the polycrystalline rod. Single crystals of Bi&,CarCu,O, were grown by using the crystalline boule as seed and the polycrystalline rod as feed. In the growth process, the platinum strip was maintained just above the melting point of the material. The seed rod rotation of 5 r-pm was used for thorough stirring of the melt. The automatic vertical downward pull was started at a rate of 1 mm/h when an appropriate interface was formed. After the growth was over, the temperature of
0
1992 - Elsevier
Sequoia. All rights reserved
282
the platinum strip was kept constant for 5 hours without pulling. Then the temperature was reduced gradually to 300 “C and quenched to room temperature. Finally the crystal boule was annealed at 800 “C in air for 48 hours. The preferred orientation of the elongated superconducting grain in the grown boule was confirmed by a Leitz optical microscope. The X-ray powder diffraction studies were made at room temperature with CuKcv radiation to confirm the phase of the grown crystal. The composition of the grown crystals were analyzed by an electron probe micro analyzer on the surface perpendicular to the growth axis. The DC four probe technique was used to measure the resistance of the sample with an input excitation current of 10 mA. The contacts were made, using silver paint, on the surface perpendicular to the growth axis of the crystal boule.
Results
Fig. 2. Optical micrograph of a cleaved surface along the growth axis (arrow indicates the growth axis).
and discussion
The as grown boule with seed is shown in Fig. 1. The surface of the grown boule along the growth axis shows a highly textured surface morphology (Fig. 2). The crystals are prolonged along the ingot axis and the ab plane is perpendicular to the melt surface. Figure 3 shows the optical micrograph of the aggregation of platelet crystals aligned parallel to each other along the pulling direction. The single crystals were picked up from the crystal boule by cleaving along the growth axis. The phase of the grown crystal and the cell constants were determined from the powder X-ray diffractogram of the crystal boule (Fig. 4). It reveals that the grown crystal is a single phase
Fig. 1. The photograph
of a grown crystal boule with seed.
Fig. 3. Optical micrograph showing the aggregation of crystals packed along the growth axis (arrow indicates the growth axis).
(2212) with traces of B&O3 and CuO impurity peaks and 2223 phase. The observed impurity peaks may be due to the precipitation of a very small quantity of B&O3 and CuO during stable growth. This is due to the large temperature gradient experienced by the molten material at the growth zone. The presence of the 2223 phase peak may be due to the syntactic growth of various phases. The cell constants were determined as a =5.40 A, b =5.44 8, and c=30.74 A, by the least squares method. The EPMA observation (Fig. 5) of the sample shows that the zone melted sample is in the Bi 2212 phase. The chemical composition of the grown sample is close to Bi2.04Srl.8Cal.16CuzO~+~Resistive transition of the Biz.04SrI.8Ca&uz08+y crystal as a function of temperature in the annealed state is shown in Fig. 6. The crystalline ingot exhibits a T, onset at 90 K and zero resistance was measured at 82 K. The detailed field and frequency depen-
283
2223
l
z 0 0
60
55
M
45
LO
DIFFRACTION
Fig. 4. Powder X-ray diffractogram
35
ANGLE
2B
30
.
cue
.
El1203
25
20
(degrees)
of the grown crystal boule.
d Y
:
0 1 J
6 m
i
oos-
0.00
I
I
L
1
Fig. 6. Resistive transition a function of temperature.
ENERGY
Fig. 5. EPMA arbitrary).
1
6
spectrum
8
10
12
I KeV)
of Bi,,,Sr,,,Ca,.,,Cu,O,,,
(peaks
are
dence of the ac susceptibility and the current density of the textured high density samples will be reported later. Conclusion
88
116 TEMPERATURE
VJ”’
2
I 60
IL1
172 (Kl
2c
A
of Bi,,,Sr,,,Ca,.,,Cu,O,,,
crystal as
nique. This method presents some advantages over the conventional floating zone technique. Unlike in the conventional floating zone process the melt zone is usually very stable with precise control over the planar growth front and also the growth initiation with a seed crystal is particularly easy. The zone melted samples show a highly textured microstructure with crystals extending along the growth axis. Their X-ray diffraction pattern confirms their orthorhombic structure. The chemical composition of the grown crystal is Bi,,Sr&aI.&u~08 +,, The resistivity measurements on the grown crystals show their normal state resistivity to be linear with temperature and have zero resistance at 82 K.
284
References 1 H. Maeda, Y. Tanaka, M. Fukutomi and T. Asano, Ipn. J, A&. Phys., 27 (1989) L209. 2 J. M. Tar-axon, Y. Le Page, P. Barboux, B. G. Bagley, L. H. Greene, W. R. Mckinnon, G. W. Hull, M. Giroud and D. H. Huang, Phys. Rev. B, 37 (1988) 9382. 3 P. Sureshkumar, C. Subramaian and P. Ramasamy, Mod. Phys. Lett. B, 3 (1989) 1417. 4 H. Takagi, H. Eisaki, S. Uchida, A. Maeda, S. Tajima, K. Uchinokura and S. Tanaka, Nature, 332 (1988) 236. 5 L. F. Schneemeyer, R. B. Van Dover, S. H. Glarum, S. A. Sunshine, R. M. Fleming, B. Batlogg, T. Siegrist, J. M, Marshall, J. V. Waszczak and L. W. Rupp, Nature, 332 (1988) 422.
6 M. J. Cima, X. P. Jiang, H. M. Chow, J. S. Haggerty, M. C. Flemings, H. D. Brody, R. A. Laudise and D. W. Johnson, J. Mat. Res., 5 (1990) 1834. 7 S. Takekawa, H. Nozaki, A. Umezono, K. Kosuda and M. Kobayashi, J. Crystal Growth, 92 (1988) 687. 8 K. Tsushima, Prog. High Temp. Superconductivity, 24 (1989) 10. 9 K. Salama, V. Selvamanickam, L. Gao and K. Sun, A&. Phys. Len., 54 (1989) 2352. 10 J. J. Brissot and C. Belin, J. CIYS~.Growth, 8 (1971) 213. 11 P. R. Swinehart, J. Cryst. Growth, 26 (1974) 317. 12 M. Palaniswamy, F. D. Gnanam, P. Ramasamy and G. S. Laddha, Cvsi. Res. Technol., 17 (1982) 911. 13 R. Gopalakrishnan, D. Arivu Oh and P. Ramasamy, Cryst. Res. Technol., (in press).