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Properties and analysis of superconducting pellets and thin films of Bi-Sr-Ca-Cu-O material
applied surface science ELSEVIER
Applied Surface Science79/80 (1994)455-458
Properties and analysis of superconducting pellets and thin films of B i - S r - C a - C u - O material D . F e r r o b U . G a m b a r d e l l a a, V. M a r o t t a a R . M a r t i n o S. O r l a n d o a, G . P . P a r i s i a
a
A. Morone
.,a
a Istituto per i Materiali Speciali, Area di Ricerca di Potenza, CNR, 85050 Tito Scalo, PZ, Italy b Centro Termodinamica Chimica AT, CNR, Roma, Italy
(Received 13 October 1993; accepted for publication 5 December 1993)
Abstract
This work deals with the production and characterization of superconducting Bi-Sr-Ca-Cu-O thin films realized by using the pulsed laser deposition technique. Scanning electron microscopy, energy dispersive spectroscopy, and X-ray diffraction have been utilized to characterize the thin films. The presence of the Bi-Sr-Ca-Cu-O 2223 phase is reported.
I. Introduction
In these last years the high critical temperature transition materials (HT c) have aroused the research workers [1]. Ceramic composite materials as Y - B a - C u - O , L a - B a - C u - O and B i - S r C a - C u - O have been studied in order to improve the electrical properties like high Tc and critical current density J~ [2]. Usually these materials were prepared in powders and afterwards pelletized. Furthermore, considerable progress has been achieved in developing methods to grow thin films of these superconducting materials, with the aim of realizing electronic devices. Different techniques ranging from sputtering to laser ablation yielded high quality thin films when deposited on suitable substrates. The pulsed laser
* Corresponding author. Fax: (+ 39) 971 427 222.
deposition (PLD) features a straightforward method to grow thin films of composed materials, and in addition offers a simple deposition scheme. A laser beam enters through a window into the vacuum chamber and impinges on the material to be deposited. Laser removal of matter produces a plume in which electrons, ions and neutral species are present. The ablated material is collected on a substrate placed at a suitable distance. H T c materials require an appropriate heat treatment to get superconducting films. It is of real interest to understand the interrelationship between the chemistry, the laser ablation processes, and the resulting microstructural properties of the deposited thin film. We measured the space and time dependent emission spectra of the species present in the plume, which provided a key to understand the dynamics and reactivity of the ablated materials in the gas phase [3-5]. In our laboratory we produce PbBiSrCaCuO (PBSCCO)
0169-4332/94/$07.00 © 1994 Elsevier Science B.V. All rights reserved 0169-4332(94)00095-I
SSDI
456
D. Ferro et aL /Applied Surface Science 70/80 (1994) 455 458
2. Experimental
)000
o 2223 80o
6[)11
o
4011
o
c [ ],
200
~ o
o ~ °
~
o
18.5
34
49.5
65
20 Fig. 1. Diffraction pattern of BiPbSrCaCuO pellet: (O) 2223 phase.
pellets of the high transition t e m p e r a t u r e (To) phase (2223) on which we perform the laser ablation process with the aim to grow films of the same 2223 phase. In this paper, after a short summary of the experimental facilities, we present the analysis performed on our BSCCO thin films by means of different techniques: X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS).
The laser system consists of a frequency doubled (A : 532 nm, pulse duration 10 ns) N d - Y A G laser. The laser energy is about 2.5-3 J/cm 2, the incidence angle with respect to the target surface is 45 °. The vacuum chamber is equipped with a quartz laser entrance window faced to a rotating target holder. In front of the target, at a distance of 2.5 cm, is placed a substrate holder heated to 600°C. The chamber pressure is in the range of 10-5_10 6 mbar during the ablation process. Thin films were deposited on MgO(100) substrates by laser ablation of sintered PBSCCO pellets. The pellets were obtained by calcining mixtures of Bi20 3, PbO, CaCO3, SrCO 3 and CuO, with the aim that the Pb partial substitution of Bi promote the growth of the BSCCO 2223 high Tc phase [6,7]. The produced films of BSCCO were furnace annealed in air for 1 h at 850°C. Morphological analyses were performed by SEM having a resolution of 70 nm while the composition of pellets and thin films, both "as deposited" and after annealing, were investigated either by EDS microanalysis. Structural analyses were obtained by using Cu K a I = 1.5406 ,~ radiation.
Fig. 2. Micrograph of BiPbSrCaCuO pellet.
457
D. Ferro et al. /Applied Surface Science 79/80 (1994) 455-458
1000
3. Results and d i s c u s s i o n
Targets were p r e p a r e d in a standard way starting from Bi203, PbO, CuO and CaCO3, SrCO 3 powders, with a cationic ratio of Bi2APb0.4SrzCa 3 Cu 4 [8]. The powders were mixed together in ethanol and heated at 780°C for a few hours in air. They were subsequently calcined in air at 840°C for a duration time up to 120 h. The calcined powders were then cold pressed into pellets and isothermally sintered at 845°C for 100 h. The structure and composition of the powders and pellets were determined by X-ray diffraction and SEM-EDS measurements. Fig. 1 shows a typical X-ray diffraction pattern of the pellet, in which the 2223 phase can be identified. Fig. 2 shows a SEM micrograph of the pellet. Different orientations can be noted in the pellet, depending on the area observed. The EDS microanalyses of these crystals are a result of a spatial average of measurements on the surface. Although the cationic ratio of the powders was in average strongly deviating from the 2223 phase the composition of the pellet plate-like crystals is Bi2.tPb0aSr2Ca2Cu3.5, only slightly deviating from 2223, when considering the large uncertainties
o 2223 + 2212
800
600 +
400
÷
o °
200 +
3
18.5
o
34
49.5
65
20 Fig. 4. Diffraction pattern of BSCCO superconducting thin film. introduced by the roughness of the sample and by the use of the spot method. The resistive behavior of typical targets used for PLD has a Tc onset of 110 K, corresponding essentially to the 2223 phase, and a zero resistance temperature higher than 102 K.
Fig. 3. Micrograph of BSCCO superconducting thin film.
D. Ferro et al. /Applied Surface Science 7 9 / 8 0 ('1994) 455-458
458
l
. . . .
,
. . . .
,
. . . .
,
. . . .
,
.
.
.
.
,
. . . .
0.8 ~0.6 *~ 0.4
0.2
50
100
150
200
250
300
Temperature (K) Fig. 5. Temperature dependence of BSCCO film resistance.
A typical morphology of the ablated films after annealing is reported in Fig. 3. The presence of isolated granular structures of particles 5 - 2 0 / z m in diameter is evidenced by SEM analysis. These islands have an averaged length of 10 ~ m in which stoichiometric composition (Bil.sPb0.~Sr 2 Ca2CH3. 2) is found by EDS analysis. However, composition at the island edges is mainly of the 2212 phase with some contamination of CuCaO. In Fig. 4 the X-ray spectra of the film is reported. The presence of peaks relative to the 2223 phase is indicated by open circles, while crosses denote the peaks ascribed to the 2212 phase. Finally, in Fig. 5 is shown the resistive behavior of a BSCCO annealed film. Here the "double transition" confirms the hypotheses of the presence of both phases, being the 2223 phase not fully connected by any precolative path.
4. Summary We have sintered Pb doped BSCCO pellets exhibiting the 2223 high Tc phase either in X R D or EDS measurements. The resistive behavior
also indicates the presence of the 2223 phase. By means of PLD from these pellets we have grown BSCCO thin films and analyzed their structure as well as their critical temperature. We discuss detailed EDS data recorded on superconducting films. These results, together with XRD pattern and Tc measurements, indicate that our films grow both in the 2212 and the 2223 phase. However, even if the 2223 phase in the films is detected in small structures on the film surfaces, it is large enough to induce a clear drop of the resistance at the corresponding critical temperature of 110 K. Further work is needed in our fabrication process to improve the 2223 phase compared with the 2212 and contaminants in the films.
References [1] J.G. Bednorz and K.B. Muller, Z. Phys. B 64 (1986) 189. [2] H. Maeda, Y. Tamaka, M. Fukutomi and T. Asano, Jpn. J. Appl. Phys. 27 (1988) L209. [3] A. Giardini Guidoni, E. Desimoni, A.M. Salvi, R. Teghil, M. Ambrico, A. Morone, S. Piccirillo and M. Snels, Proc. Int. Conf. on Lasers '90 (1990) p. 331. [4] A. Giardini Guidoni, A. Morone, M. Snels, E. Desimoni, A.M. Salvi, R. Fantoni, W.C.M. Berden and M. Giorgi, Appl. Surf. Sci. 46 (1990) 321. [5] A. Mele, D. Consalvo, D. Stranges and A. Giardini Guidoni, Int. J. Mass Spectrosc. Ion. Proces. 95 (1990) 359. [6] S.A. Sunshine, T. Siegrist, L.F. Schneemeyer, D.W. Murphy, R.J. Cava, B. Batlogg, R.B. van Doover, R.M. Fleming, S.H. Glarum, S. Nakahara, R. Farrow, J.J. Krajewski, S.M. Zahurak, J,V. Waszczak, J.H. Marshall, P. Marsh, L.W. Rupp, Jr. and W.F. Peck, Phys. Rev. B 38 (1988) 893. [7] W. Kulda, R. Sobolewski, J. Gorecka and S.J. Lewandoski, J. Appl. Phys. 70 (1991) 3171. [8] C. Alvani, M. Penna, V. Boffa and G. Patern6, in: Proc. First Italian Workshop on Laser Deposition of Advanced Materials, Tito (PZ), Italy, September 28-3(I, 1992, Eds. M. Allegrini, A. Giardini Guidoni and A. Morone, ETS (1992) p. 67.
Applied Surface Science79/80 (1994)455-458
Properties and analysis of superconducting pellets and thin films of B i - S r - C a - C u - O material D . F e r r o b U . G a m b a r d e l l a a, V. M a r o t t a a R . M a r t i n o S. O r l a n d o a, G . P . P a r i s i a
a
A. Morone
.,a
a Istituto per i Materiali Speciali, Area di Ricerca di Potenza, CNR, 85050 Tito Scalo, PZ, Italy b Centro Termodinamica Chimica AT, CNR, Roma, Italy
(Received 13 October 1993; accepted for publication 5 December 1993)
Abstract
This work deals with the production and characterization of superconducting Bi-Sr-Ca-Cu-O thin films realized by using the pulsed laser deposition technique. Scanning electron microscopy, energy dispersive spectroscopy, and X-ray diffraction have been utilized to characterize the thin films. The presence of the Bi-Sr-Ca-Cu-O 2223 phase is reported.
I. Introduction
In these last years the high critical temperature transition materials (HT c) have aroused the research workers [1]. Ceramic composite materials as Y - B a - C u - O , L a - B a - C u - O and B i - S r C a - C u - O have been studied in order to improve the electrical properties like high Tc and critical current density J~ [2]. Usually these materials were prepared in powders and afterwards pelletized. Furthermore, considerable progress has been achieved in developing methods to grow thin films of these superconducting materials, with the aim of realizing electronic devices. Different techniques ranging from sputtering to laser ablation yielded high quality thin films when deposited on suitable substrates. The pulsed laser
* Corresponding author. Fax: (+ 39) 971 427 222.
deposition (PLD) features a straightforward method to grow thin films of composed materials, and in addition offers a simple deposition scheme. A laser beam enters through a window into the vacuum chamber and impinges on the material to be deposited. Laser removal of matter produces a plume in which electrons, ions and neutral species are present. The ablated material is collected on a substrate placed at a suitable distance. H T c materials require an appropriate heat treatment to get superconducting films. It is of real interest to understand the interrelationship between the chemistry, the laser ablation processes, and the resulting microstructural properties of the deposited thin film. We measured the space and time dependent emission spectra of the species present in the plume, which provided a key to understand the dynamics and reactivity of the ablated materials in the gas phase [3-5]. In our laboratory we produce PbBiSrCaCuO (PBSCCO)
0169-4332/94/$07.00 © 1994 Elsevier Science B.V. All rights reserved 0169-4332(94)00095-I
SSDI
456
D. Ferro et aL /Applied Surface Science 70/80 (1994) 455 458
2. Experimental
)000
o 2223 80o
6[)11
o
4011
o
c [ ],
200
~ o
o ~ °
~
o
18.5
34
49.5
65
20 Fig. 1. Diffraction pattern of BiPbSrCaCuO pellet: (O) 2223 phase.
pellets of the high transition t e m p e r a t u r e (To) phase (2223) on which we perform the laser ablation process with the aim to grow films of the same 2223 phase. In this paper, after a short summary of the experimental facilities, we present the analysis performed on our BSCCO thin films by means of different techniques: X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS).
The laser system consists of a frequency doubled (A : 532 nm, pulse duration 10 ns) N d - Y A G laser. The laser energy is about 2.5-3 J/cm 2, the incidence angle with respect to the target surface is 45 °. The vacuum chamber is equipped with a quartz laser entrance window faced to a rotating target holder. In front of the target, at a distance of 2.5 cm, is placed a substrate holder heated to 600°C. The chamber pressure is in the range of 10-5_10 6 mbar during the ablation process. Thin films were deposited on MgO(100) substrates by laser ablation of sintered PBSCCO pellets. The pellets were obtained by calcining mixtures of Bi20 3, PbO, CaCO3, SrCO 3 and CuO, with the aim that the Pb partial substitution of Bi promote the growth of the BSCCO 2223 high Tc phase [6,7]. The produced films of BSCCO were furnace annealed in air for 1 h at 850°C. Morphological analyses were performed by SEM having a resolution of 70 nm while the composition of pellets and thin films, both "as deposited" and after annealing, were investigated either by EDS microanalysis. Structural analyses were obtained by using Cu K a I = 1.5406 ,~ radiation.
Fig. 2. Micrograph of BiPbSrCaCuO pellet.
457
D. Ferro et al. /Applied Surface Science 79/80 (1994) 455-458
1000
3. Results and d i s c u s s i o n
Targets were p r e p a r e d in a standard way starting from Bi203, PbO, CuO and CaCO3, SrCO 3 powders, with a cationic ratio of Bi2APb0.4SrzCa 3 Cu 4 [8]. The powders were mixed together in ethanol and heated at 780°C for a few hours in air. They were subsequently calcined in air at 840°C for a duration time up to 120 h. The calcined powders were then cold pressed into pellets and isothermally sintered at 845°C for 100 h. The structure and composition of the powders and pellets were determined by X-ray diffraction and SEM-EDS measurements. Fig. 1 shows a typical X-ray diffraction pattern of the pellet, in which the 2223 phase can be identified. Fig. 2 shows a SEM micrograph of the pellet. Different orientations can be noted in the pellet, depending on the area observed. The EDS microanalyses of these crystals are a result of a spatial average of measurements on the surface. Although the cationic ratio of the powders was in average strongly deviating from the 2223 phase the composition of the pellet plate-like crystals is Bi2.tPb0aSr2Ca2Cu3.5, only slightly deviating from 2223, when considering the large uncertainties
o 2223 + 2212
800
600 +
400
÷
o °
200 +
3
18.5
o
34
49.5
65
20 Fig. 4. Diffraction pattern of BSCCO superconducting thin film. introduced by the roughness of the sample and by the use of the spot method. The resistive behavior of typical targets used for PLD has a Tc onset of 110 K, corresponding essentially to the 2223 phase, and a zero resistance temperature higher than 102 K.
Fig. 3. Micrograph of BSCCO superconducting thin film.
D. Ferro et al. /Applied Surface Science 7 9 / 8 0 ('1994) 455-458
458
l
. . . .
,
. . . .
,
. . . .
,
. . . .
,
.
.
.
.
,
. . . .
0.8 ~0.6 *~ 0.4
0.2
50
100
150
200
250
300
Temperature (K) Fig. 5. Temperature dependence of BSCCO film resistance.
A typical morphology of the ablated films after annealing is reported in Fig. 3. The presence of isolated granular structures of particles 5 - 2 0 / z m in diameter is evidenced by SEM analysis. These islands have an averaged length of 10 ~ m in which stoichiometric composition (Bil.sPb0.~Sr 2 Ca2CH3. 2) is found by EDS analysis. However, composition at the island edges is mainly of the 2212 phase with some contamination of CuCaO. In Fig. 4 the X-ray spectra of the film is reported. The presence of peaks relative to the 2223 phase is indicated by open circles, while crosses denote the peaks ascribed to the 2212 phase. Finally, in Fig. 5 is shown the resistive behavior of a BSCCO annealed film. Here the "double transition" confirms the hypotheses of the presence of both phases, being the 2223 phase not fully connected by any precolative path.
4. Summary We have sintered Pb doped BSCCO pellets exhibiting the 2223 high Tc phase either in X R D or EDS measurements. The resistive behavior
also indicates the presence of the 2223 phase. By means of PLD from these pellets we have grown BSCCO thin films and analyzed their structure as well as their critical temperature. We discuss detailed EDS data recorded on superconducting films. These results, together with XRD pattern and Tc measurements, indicate that our films grow both in the 2212 and the 2223 phase. However, even if the 2223 phase in the films is detected in small structures on the film surfaces, it is large enough to induce a clear drop of the resistance at the corresponding critical temperature of 110 K. Further work is needed in our fabrication process to improve the 2223 phase compared with the 2212 and contaminants in the films.
References [1] J.G. Bednorz and K.B. Muller, Z. Phys. B 64 (1986) 189. [2] H. Maeda, Y. Tamaka, M. Fukutomi and T. Asano, Jpn. J. Appl. Phys. 27 (1988) L209. [3] A. Giardini Guidoni, E. Desimoni, A.M. Salvi, R. Teghil, M. Ambrico, A. Morone, S. Piccirillo and M. Snels, Proc. Int. Conf. on Lasers '90 (1990) p. 331. [4] A. Giardini Guidoni, A. Morone, M. Snels, E. Desimoni, A.M. Salvi, R. Fantoni, W.C.M. Berden and M. Giorgi, Appl. Surf. Sci. 46 (1990) 321. [5] A. Mele, D. Consalvo, D. Stranges and A. Giardini Guidoni, Int. J. Mass Spectrosc. Ion. Proces. 95 (1990) 359. [6] S.A. Sunshine, T. Siegrist, L.F. Schneemeyer, D.W. Murphy, R.J. Cava, B. Batlogg, R.B. van Doover, R.M. Fleming, S.H. Glarum, S. Nakahara, R. Farrow, J.J. Krajewski, S.M. Zahurak, J,V. Waszczak, J.H. Marshall, P. Marsh, L.W. Rupp, Jr. and W.F. Peck, Phys. Rev. B 38 (1988) 893. [7] W. Kulda, R. Sobolewski, J. Gorecka and S.J. Lewandoski, J. Appl. Phys. 70 (1991) 3171. [8] C. Alvani, M. Penna, V. Boffa and G. Patern6, in: Proc. First Italian Workshop on Laser Deposition of Advanced Materials, Tito (PZ), Italy, September 28-3(I, 1992, Eds. M. Allegrini, A. Giardini Guidoni and A. Morone, ETS (1992) p. 67.