- Email: [email protected]
Preparation of high-Tc superconductors by electrophoretic deposition method
PHYSICA
Physica C 190 ( 1991 ) 163-164 North-Holland
Preparation of high-To superconductors by electrophoretic deposition method Study on the substrate and the electrolyte N. Koura and H. Shoji Department of Industrial Chemistry, Faculty of Science and Technology, Science University of Tokyo, 2641 Yamazaki, Noda-shi 278, Japan
Variously shaped superconducting oxides with various substrates have been prepared by the electrophoretic deposition method. The maximum Jc was about 600 A/cm 2, because the oxides were fairly porous. Therefore, the deposition was attempted at high voltages for the substrate having a thermal expansivity close to that of the oxides. In the case of the stainless steel ( 19Cr-I 3Ni3Si-0.1Nb), the superconducting phase did not have cracks, even if it was deposited at high voltage. Moreover, the preparation of BSCCO superconductor was studied by this method.
1. Introduction
3. Results and discussion
Variously shaped superconducting oxides with various substrates have been prepared by the electrophoretic deposition method [ 1-7]. In the case of A1~O3 ceramics or silver substrates, the coated oxides were uniform. Their thicknesses were about 200 ~tm. Their XRD patterns coincided completely with that of YBa2Cu3OT_~. Their Tcs were about 90 K. But, the maximum Jr was about 600 A / c m z, because the coating was fairly porous. Therefore, the deposition was attempted at high voltages for the substrate having a thermal expansivity close to that of the superconductor in order to increase the J¢ value. Furthermore, the influence of diffusion of metals from the substrate was studied. The preparation of BSCCO superconductor was also attempted.
In the case of a silver substrate, the samples deposited at high voltages had some cracks after being sintered. This was attributed to the difference in the thermal expansivities of silver and YBCO. Then, we attempted stainless steel substrates. In the case of the ferrite steel (19Cr-13Ni-3Si0.1Nb), the oxides layer did not have cracks, even if the deposition was done at high voltage. However, diffusion of Ni, Cr, and Fe to the superconducting phase occurred. Then, we studied to control the diffusion as below. The restraint of the diffusion from the stainless steel was attempted by changing of sintering and annealing conditions. When the sintering temperature was changed, the relationship between the resistivity and the temperature ( R -
2. Experimental 5.0
The calcined YBCO powder was suspended in an acetone bath ( 100 ml acetone+ 20 mg 12+0.3 ml H 2 0 + 1.0 g YBCO) by an ultrasonic washing machine. The electrolyte for the electrophoretic deposition was the acetone bath, the negative electrode was Ag substrate, and the positive electrode was Pt wire. The superconductor coated material was heattreated at 940°C (6 h), then annealed at 500°C (4 h). The resistivity was measured by the DC four-probe method.
4.0
_~ 3.0 2.0
0
1O0
200
300
Temperal~re, T I K
Fig. I. Resistivity-temperaturecurves for various sintering temperatures. Substrate: 19Cr-13Ni-3Si-0.1Nb (1) 900°C, (2) 920°C, (3) 940°C.
0921-4534/91/$03.50 © 1991 Elsevier Science Publishers B.V. All rights reserved.
N. Koura, H. Shoji / Preparation of HTSC by electrophoretic deposition
164
5.0
YBCO
4.0
~ ( 1 ) Z r O 2 or (2lAg I "4-~ 19Cr -I 3 N i - 3 S i - 0. INb
3.0 '~
2.0 1.0
100
200
300
Temperature, T / K
Fig. 2. Resistivity-temperature curves. Substrate: 19Cr-I 3Ni3Si-0.1Nb. Buffering layer: ZrO2 or Ag.
5.0
4.0 --
i ¢
3.0
~
(a)
(a)
(C)
I00
0
200
300
Temperature, T / K
Fig. 3. Resistivity-temperature curves for BSCCO. (a) Acetone bath, (b) n-hexane bath, (c) toluene bath.
5.0
..... O v,~
oo
4.0
0
'7
o
3.0
OO
nealing temperature of 400 ° C, a part of a shoulder appeared on the R - T curve, and zero resistivity was not obtained. But in the case of 500°C, the Tc was about 50 K. The restraint of the diffusion of metals from the substrate was studied by a metal and a ceramics coating on the substrafe as buffering layer. In the case of the zirconia coating by an electrophoretic deposition method, the Tc rose to about 82 K as shown in fig. 2. Moreover, the shoulder on the R T curve disappeared, and the resistivity behavior was like that of a metal. In the case of the silver coating by an electroless plating method, the Tc also rose to about 73 K. The preparation of BSCCO superconductor has been investigated. The resistivity behavior of the sample prepared from the acetone bath was like that of a semiconductor at the normal conductive range (fig. 3). The transition to the superconducting state was gradual, although the high-To phase existed. The Tc was about 15 K. It was considered that the superconductivity was deteriorated, because the BSCCO reacted with ketones. Then we studied the solvents which do not react with the BSCCO. Toluene and n-hexane were selected. The electrophoretic deposition baths with these sotvents were prepared as follows. In the case of the n-hexane bath, the bath was 20-40 ml acetone+0.1 g nitrocellul o s e + 6 0 - 8 0 ml n-hexane+2.0 g BSCCO powder; the applied voltage was 100-200 V. In the case of the toluene bath, the bath was 100 ml toluene+2.0 g BSCCO powder; the applied voltage was 1000-1500 V. In the case of the n-hexane bath, the amount of deposit was small. In the case of a toluene bath, the amount of deposit increased with increasing voltage (fig. 4). Resistivity measurements were carried out about these samples. These were obviously different from the samples prepared from the acetone and ethanol baths. The resistivity decreased with decreasing temperature like that of a metal at the normal conductive range. Their Tcs were 45 and 50 K, respectively (fig. 3).
0 ,~
2.0
References
o < 1.o
0 0
~o o00 0
,
i000
2000
Vdtage/V
Fig. 4. Relationship between the amount of deposit and the applied voltage (toluene bath). Tcurve) was obtained as shown infig. 1. From 920 to 940°C, the resistivity increased with decreasing temperature like that of a semiconductor. Their Tcs were about 50 K. Furthermore, the T~ rose with increasing sintering time. Next, the annealing temperature was changed. In the case of an an-
[ 1 ] N. Koura, Denki Kagaku 56 (1988) 208. [2] N. Koura, N. Takami andY. Mikuriya, MRS Int. Meet. Adv. Mater. 6 (1989) 193. [ 3 ] N. Koura and Y. Mikuriya, J. Surf. Fin. Soc. Jpn. 40 (1989) 72. [4] N. Koura and Y. Mikuriya, J. Surf. Fin. Soc. Jpn. 40 (1989) 819. [5] N. Koura, Y. Mikuriya and H. Shoji, Hyomen 27 (1989) 719. [6] N. Koura, H. Shoji and A. Morita, Mol. Cryst. Liq. Cryst. 184 (1990) 243. [ 7 ] N. Koura and H. Shoji, J. Surf. Fin. Soc. Jpn. 42 ( 1991 ) 508.
Physica C 190 ( 1991 ) 163-164 North-Holland
Preparation of high-To superconductors by electrophoretic deposition method Study on the substrate and the electrolyte N. Koura and H. Shoji Department of Industrial Chemistry, Faculty of Science and Technology, Science University of Tokyo, 2641 Yamazaki, Noda-shi 278, Japan
Variously shaped superconducting oxides with various substrates have been prepared by the electrophoretic deposition method. The maximum Jc was about 600 A/cm 2, because the oxides were fairly porous. Therefore, the deposition was attempted at high voltages for the substrate having a thermal expansivity close to that of the oxides. In the case of the stainless steel ( 19Cr-I 3Ni3Si-0.1Nb), the superconducting phase did not have cracks, even if it was deposited at high voltage. Moreover, the preparation of BSCCO superconductor was studied by this method.
1. Introduction
3. Results and discussion
Variously shaped superconducting oxides with various substrates have been prepared by the electrophoretic deposition method [ 1-7]. In the case of A1~O3 ceramics or silver substrates, the coated oxides were uniform. Their thicknesses were about 200 ~tm. Their XRD patterns coincided completely with that of YBa2Cu3OT_~. Their Tcs were about 90 K. But, the maximum Jr was about 600 A / c m z, because the coating was fairly porous. Therefore, the deposition was attempted at high voltages for the substrate having a thermal expansivity close to that of the superconductor in order to increase the J¢ value. Furthermore, the influence of diffusion of metals from the substrate was studied. The preparation of BSCCO superconductor was also attempted.
In the case of a silver substrate, the samples deposited at high voltages had some cracks after being sintered. This was attributed to the difference in the thermal expansivities of silver and YBCO. Then, we attempted stainless steel substrates. In the case of the ferrite steel (19Cr-13Ni-3Si0.1Nb), the oxides layer did not have cracks, even if the deposition was done at high voltage. However, diffusion of Ni, Cr, and Fe to the superconducting phase occurred. Then, we studied to control the diffusion as below. The restraint of the diffusion from the stainless steel was attempted by changing of sintering and annealing conditions. When the sintering temperature was changed, the relationship between the resistivity and the temperature ( R -
2. Experimental 5.0
The calcined YBCO powder was suspended in an acetone bath ( 100 ml acetone+ 20 mg 12+0.3 ml H 2 0 + 1.0 g YBCO) by an ultrasonic washing machine. The electrolyte for the electrophoretic deposition was the acetone bath, the negative electrode was Ag substrate, and the positive electrode was Pt wire. The superconductor coated material was heattreated at 940°C (6 h), then annealed at 500°C (4 h). The resistivity was measured by the DC four-probe method.
4.0
_~ 3.0 2.0
0
1O0
200
300
Temperal~re, T I K
Fig. I. Resistivity-temperaturecurves for various sintering temperatures. Substrate: 19Cr-13Ni-3Si-0.1Nb (1) 900°C, (2) 920°C, (3) 940°C.
0921-4534/91/$03.50 © 1991 Elsevier Science Publishers B.V. All rights reserved.
N. Koura, H. Shoji / Preparation of HTSC by electrophoretic deposition
164
5.0
YBCO
4.0
~ ( 1 ) Z r O 2 or (2lAg I "4-~ 19Cr -I 3 N i - 3 S i - 0. INb
3.0 '~
2.0 1.0
100
200
300
Temperature, T / K
Fig. 2. Resistivity-temperature curves. Substrate: 19Cr-I 3Ni3Si-0.1Nb. Buffering layer: ZrO2 or Ag.
5.0
4.0 --
i ¢
3.0
~
(a)
(a)
(C)
I00
0
200
300
Temperature, T / K
Fig. 3. Resistivity-temperature curves for BSCCO. (a) Acetone bath, (b) n-hexane bath, (c) toluene bath.
5.0
..... O v,~
oo
4.0
0
'7
o
3.0
OO
nealing temperature of 400 ° C, a part of a shoulder appeared on the R - T curve, and zero resistivity was not obtained. But in the case of 500°C, the Tc was about 50 K. The restraint of the diffusion of metals from the substrate was studied by a metal and a ceramics coating on the substrafe as buffering layer. In the case of the zirconia coating by an electrophoretic deposition method, the Tc rose to about 82 K as shown in fig. 2. Moreover, the shoulder on the R T curve disappeared, and the resistivity behavior was like that of a metal. In the case of the silver coating by an electroless plating method, the Tc also rose to about 73 K. The preparation of BSCCO superconductor has been investigated. The resistivity behavior of the sample prepared from the acetone bath was like that of a semiconductor at the normal conductive range (fig. 3). The transition to the superconducting state was gradual, although the high-To phase existed. The Tc was about 15 K. It was considered that the superconductivity was deteriorated, because the BSCCO reacted with ketones. Then we studied the solvents which do not react with the BSCCO. Toluene and n-hexane were selected. The electrophoretic deposition baths with these sotvents were prepared as follows. In the case of the n-hexane bath, the bath was 20-40 ml acetone+0.1 g nitrocellul o s e + 6 0 - 8 0 ml n-hexane+2.0 g BSCCO powder; the applied voltage was 100-200 V. In the case of the toluene bath, the bath was 100 ml toluene+2.0 g BSCCO powder; the applied voltage was 1000-1500 V. In the case of the n-hexane bath, the amount of deposit was small. In the case of a toluene bath, the amount of deposit increased with increasing voltage (fig. 4). Resistivity measurements were carried out about these samples. These were obviously different from the samples prepared from the acetone and ethanol baths. The resistivity decreased with decreasing temperature like that of a metal at the normal conductive range. Their Tcs were 45 and 50 K, respectively (fig. 3).
0 ,~
2.0
References
o < 1.o
0 0
~o o00 0
,
i000
2000
Vdtage/V
Fig. 4. Relationship between the amount of deposit and the applied voltage (toluene bath). Tcurve) was obtained as shown infig. 1. From 920 to 940°C, the resistivity increased with decreasing temperature like that of a semiconductor. Their Tcs were about 50 K. Furthermore, the T~ rose with increasing sintering time. Next, the annealing temperature was changed. In the case of an an-
[ 1 ] N. Koura, Denki Kagaku 56 (1988) 208. [2] N. Koura, N. Takami andY. Mikuriya, MRS Int. Meet. Adv. Mater. 6 (1989) 193. [ 3 ] N. Koura and Y. Mikuriya, J. Surf. Fin. Soc. Jpn. 40 (1989) 72. [4] N. Koura and Y. Mikuriya, J. Surf. Fin. Soc. Jpn. 40 (1989) 819. [5] N. Koura, Y. Mikuriya and H. Shoji, Hyomen 27 (1989) 719. [6] N. Koura, H. Shoji and A. Morita, Mol. Cryst. Liq. Cryst. 184 (1990) 243. [ 7 ] N. Koura and H. Shoji, J. Surf. Fin. Soc. Jpn. 42 ( 1991 ) 508.