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Influence of B, Al, Ga, In on the composition of Bi(Pb)SrCaCuO system
Physica B 321 (2002) 295–297
Influence of B, Al, Ga, In on the composition of Bi(Pb)SrCaCuO system D. Sy! korova! a,*, O. Smrc$ kova! a, K. Rubes$ova! a, K. Kn!ız$ ekb a
Department of Inorganic Chemistry, Institute of Chemical Technology, Technicka! 5, 166 28 Prague 6, Czech Republic b Institute of Physics, 162 53 Cukrovarnicka! 10, Prague 6, Czech Republic
Abstract Samples with partial cationic substitution for bismuth in Bi(Pb)–Sr–Ca–Cu–O system were prepared to systematically examine phase formation due to different concentrations of B, Al, Ga and In. The elements were substituted in the range x ¼ 020:5 in the nominal formula Bi1.8xAxPb0.26Sr2Ca2Cu3Oy. X-ray diffraction analysis was carried out for phase analysis with special emphasis to detect impurity phases. All the samples were mixed phases of 2212 and 2223. Rietveld analysis was used to find out the ratio of the phases. Boron enhanced the formation of the 2223 phase up to x ¼ 0:5; but gallium deteriorated the high-temperature phase 2223 and the 2212 phase became dominant. The amount of 2223 phase was increased with increasing content of Al and In (up to x ¼ 0:2) and then was decreased. The lattice parameters of the superconducting phases were obtained, and no systematic variations with the dopant level were found. Scanning electron microscopy observations revealed the presence of small and irregular amounts of Ga and In in the chemical composition of superconducting grains and the existence of the various non-superconducting phases. Superconducting properties of the samples were characterized by the measurement of the temperature dependence of the electrical and magnetic properties. r 2002 Elsevier Science B.V. All rights reserved. Keywords: BiSrCaCuO; Substitution; Phase structure
1. Introduction The partial substitution of various elements in the basic composition of superconducting material Bi–Sr–Ca–Cu–O has been studied to enhance the volume of the phase Bi-2223 with the highest critical temperature. The substitution of Pb for Bi has been reported to be very effective in increasing the amount of the high-Tc phase [1]. The Bi-2223 phase precipitates from a partially melted liquid phase [2], and the favourable sintering temperature range for the formation of *Corresponding author. Fax: +420-2-243-11010. E-mail address: [email protected] (D. S!ykorov!a).
this phase is limited and is just below the melting temperature [3]. Some additives can act as a flux which has a melting point lower than the sintering temperature and it could increase the temperature range in which the high-Tc phase is formed. Many studies have been carried out on the effect of the substitution or doping by different elements on the physical, electrical and magnetic properties [4]. Most of the results demonstrated no significant changes in the structural parameters, but in some cases, important changes occurred in the carrier concentration due to different cation doping levels [5]. Some of the elements were also found to be high-Tc phase stabilizers [6].
0921-4526/02/$ - see front matter r 2002 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 1 - 4 5 2 6 ( 0 2 ) 0 0 8 6 4 - 5
! D. Sykorov a! et al. / Physica B 321 (2002) 295–297
Addition of a second phase can lead to a modification of the microstructure, and, in particular, the fine precipitates of the second phase can act as effective pinning centres. This work reports a systematic investigation of the effect of oxides of 3.A elements of the periodic table on the phase composition in the Bi(Pb)–Sr– Ca–Cu–O system.
2. Experimental details Samples with nominal composition Bi1.8xAxPb0.26Sr2Ca2Cu3Oy, A=B, Al, Ga, In and x ¼ 020:5 were prepared by solid state reaction. Powders of oxides and carbonates were mixed together in the molar ratios, ground and calcined repeatedly at 7501C, 7701C and 7901C for 24 h in air. The calcined powders were reground, pressed into pellets and sintered at 8401C for 168 h and then air-quenched. Their superconducting properties were evaluated by resistivity measurements using a standard four-probe method and from both AC and DC susceptibility using an SQUID susceptometer. The structure of each sample was checked by X-ray diffraction using DRON 3 with CuKa radiation. The microstructure was measured with the help of scanning electron microscopy using spectrometer JXA 733 fy JEOL.
3. Results and discussion All X-ray diffractograms of the substituted samples Bi1.8xAxPb0.26Sr2Ca2Cu3Oy, A=B, Al, Ga, In and x ¼ 020:5 showed a mixture of phases Bi-2212 and Bi-2223. Some small unidentified peaks were observed and their intensities were not in relation with the amounts of dopant elements. The proportion of the Bi-2223 phase in the volume of the superconducting phases was computed by the Rietveld analysis. The results are shown in Table 1. In the boron-substituted samples, the volume of Bi-2223 phase increased from 20% to 42% for sample (Fig. 1) with the highest content of B
Table 1 The relation between volume of 2212/2223 phases and concentration of additives (x) Volume 2212/2223 phases (%) x
Boron
Aluminium
Gallium
Indium
0 0.05 0.1 0.15 0.2 0.3 0.4 0.5
81/19 79/21 85/15 82/18 70/30 63/37 71/29 58/42
81/19 67/33 86/14 84/16 82/18 90/10 92/8 92/8
81/19 75/25 89/11 89/11 94/6 96/4 97/3 97/3
81/19 78/22 79/21 72/28 76/24 80/20 87/13 100/0
% 2223
296
45 40 35 30 25 20 15 10 5 0
B Al Ga In
0.0
0.1
0.2
0.3
0.4
0.5
x
Fig. 1. The content of 2223 phase as the function of concentration of additives (x),
(x ¼ 0:5). The result confirms the favourable influence of B2O3 (melting temperature 4501C) on the formation of Bi-2223 phase. XRD analysis did not identify any secondary phases. A small addition of Al2O3 and Ga2O3 (x ¼ 0:05) increased the volume of high-Tc 2223 phase, but the higher content of these additives stabilized the Bi-2212 phase. Indium had a positive influence on the formation of Bi-2223 phase up to x ¼ 0:15 and the with highest content of In, this phase disappears. A deeper analysis of the nature of the additives containing phases and the morphology of some samples (x ¼ 0:3 and 0.5) has been performed by scanning electron microscopy. It was not possible to detect boron in the samples due its low mass and low concentration. The phases surrounding
30.840
37.400
30.830
37.350 c (x 10-1 nm)
c (x 10-1 nm)
! D. Sykorov a! et al. / Physica B 321 (2002) 295–297
30.820 30.810 30.800 30.790
297
37.300 37.250 37.200 37.150 37.100
0
0.1
0.2 x
0.3
0.4 B Ga
0.5
0
Al In
0.1
0.2
x
0.3 B Ga
0.4 Al In
Fig. 2. The lattice parameter c for the 2212 phase.
Fig. 3. The lattice parameter c for the 2223 phase.
one phase region Bi-2223 have been identified [7]: Bi-2212, (Ca, Sr)14Cu24Ox=1424, (Ca, Sr)2CuO3=21 and CuO. These phases contained only a small amount (o1 at%) of additives. Some mixed oxides with a higher content of Al, Ga and In (4–20 at%) were found, for example: Bi7Sr13Ca3CuAl19O56.5, Bi2Sr5Ca7Cu4Ga4.5O27, Bi1.5Sr14Ca5Cu23In4.5O51. The experimental results did not detect the additives that took part in the structure of the superconducting phases. This is supported by little changes in the lattice parameters of the Bi-2212 and Bi-2223 phases (Figs. 2 and 3). All the samples where Bi was partially substituted by B and Al exhibited reproducible superconducting behaviour with Tc (determined from the inflection point of the resistance curve) in range 105–110 K. The samples with Ga had Tc B105 K up to x ¼ 0:2: When the content of Ga was higher, only the Bi-2212 phase was present. Indium-substituted samples had sharp transitions at 106–107 K up to x ¼ 0:4; and the sample with x ¼ 0:5 had Tc ¼ 74; 5 K (Bi-2212 phase). Samples with B (x ¼ 0:3), Al (x ¼ 0:05) and Ga
(x ¼ 0:15) had much higher values of critical current density when compared with samples without additives [8]. This observation resulted in our opinion that the secondary phases acting as pinning centres are probably formed.
Acknowledgements This work was supported by GACR under projects 104/99/1440 and 106/99/1441.
References [1] M. Takano, et al., Jpn. J. Appl. Phys. 27 (1988) L1041. [2] J.C. Grivel, R. Flukiger, . Superlattices Microstruct. 25 (1999) 527. [3] H. Nobumasa, et al., Jpn. J. Appl. Phys. 27 (1988) L864. [4] S. Sunshine, et al., Phys. Rev. B 38 (1988) 893. [5] L. Dimesso, et al., Physica C 227 (1994) 291. [6] M.E. Yakinci, et al., Physica C 235–240 (1994) 959. [7] P. Majewski, et al., J. Am. Ceram. Soc. 80 (1997) 1174. [8] O. Smr$ckov!a, D. S!ykorov!a, K. Rube$sov!a, P. Va$sek, in these Proceedings (MSM 2001), Physica B 321 (2002).
Influence of B, Al, Ga, In on the composition of Bi(Pb)SrCaCuO system D. Sy! korova! a,*, O. Smrc$ kova! a, K. Rubes$ova! a, K. Kn!ız$ ekb a
Department of Inorganic Chemistry, Institute of Chemical Technology, Technicka! 5, 166 28 Prague 6, Czech Republic b Institute of Physics, 162 53 Cukrovarnicka! 10, Prague 6, Czech Republic
Abstract Samples with partial cationic substitution for bismuth in Bi(Pb)–Sr–Ca–Cu–O system were prepared to systematically examine phase formation due to different concentrations of B, Al, Ga and In. The elements were substituted in the range x ¼ 020:5 in the nominal formula Bi1.8xAxPb0.26Sr2Ca2Cu3Oy. X-ray diffraction analysis was carried out for phase analysis with special emphasis to detect impurity phases. All the samples were mixed phases of 2212 and 2223. Rietveld analysis was used to find out the ratio of the phases. Boron enhanced the formation of the 2223 phase up to x ¼ 0:5; but gallium deteriorated the high-temperature phase 2223 and the 2212 phase became dominant. The amount of 2223 phase was increased with increasing content of Al and In (up to x ¼ 0:2) and then was decreased. The lattice parameters of the superconducting phases were obtained, and no systematic variations with the dopant level were found. Scanning electron microscopy observations revealed the presence of small and irregular amounts of Ga and In in the chemical composition of superconducting grains and the existence of the various non-superconducting phases. Superconducting properties of the samples were characterized by the measurement of the temperature dependence of the electrical and magnetic properties. r 2002 Elsevier Science B.V. All rights reserved. Keywords: BiSrCaCuO; Substitution; Phase structure
1. Introduction The partial substitution of various elements in the basic composition of superconducting material Bi–Sr–Ca–Cu–O has been studied to enhance the volume of the phase Bi-2223 with the highest critical temperature. The substitution of Pb for Bi has been reported to be very effective in increasing the amount of the high-Tc phase [1]. The Bi-2223 phase precipitates from a partially melted liquid phase [2], and the favourable sintering temperature range for the formation of *Corresponding author. Fax: +420-2-243-11010. E-mail address: [email protected] (D. S!ykorov!a).
this phase is limited and is just below the melting temperature [3]. Some additives can act as a flux which has a melting point lower than the sintering temperature and it could increase the temperature range in which the high-Tc phase is formed. Many studies have been carried out on the effect of the substitution or doping by different elements on the physical, electrical and magnetic properties [4]. Most of the results demonstrated no significant changes in the structural parameters, but in some cases, important changes occurred in the carrier concentration due to different cation doping levels [5]. Some of the elements were also found to be high-Tc phase stabilizers [6].
0921-4526/02/$ - see front matter r 2002 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 1 - 4 5 2 6 ( 0 2 ) 0 0 8 6 4 - 5
! D. Sykorov a! et al. / Physica B 321 (2002) 295–297
Addition of a second phase can lead to a modification of the microstructure, and, in particular, the fine precipitates of the second phase can act as effective pinning centres. This work reports a systematic investigation of the effect of oxides of 3.A elements of the periodic table on the phase composition in the Bi(Pb)–Sr– Ca–Cu–O system.
2. Experimental details Samples with nominal composition Bi1.8xAxPb0.26Sr2Ca2Cu3Oy, A=B, Al, Ga, In and x ¼ 020:5 were prepared by solid state reaction. Powders of oxides and carbonates were mixed together in the molar ratios, ground and calcined repeatedly at 7501C, 7701C and 7901C for 24 h in air. The calcined powders were reground, pressed into pellets and sintered at 8401C for 168 h and then air-quenched. Their superconducting properties were evaluated by resistivity measurements using a standard four-probe method and from both AC and DC susceptibility using an SQUID susceptometer. The structure of each sample was checked by X-ray diffraction using DRON 3 with CuKa radiation. The microstructure was measured with the help of scanning electron microscopy using spectrometer JXA 733 fy JEOL.
3. Results and discussion All X-ray diffractograms of the substituted samples Bi1.8xAxPb0.26Sr2Ca2Cu3Oy, A=B, Al, Ga, In and x ¼ 020:5 showed a mixture of phases Bi-2212 and Bi-2223. Some small unidentified peaks were observed and their intensities were not in relation with the amounts of dopant elements. The proportion of the Bi-2223 phase in the volume of the superconducting phases was computed by the Rietveld analysis. The results are shown in Table 1. In the boron-substituted samples, the volume of Bi-2223 phase increased from 20% to 42% for sample (Fig. 1) with the highest content of B
Table 1 The relation between volume of 2212/2223 phases and concentration of additives (x) Volume 2212/2223 phases (%) x
Boron
Aluminium
Gallium
Indium
0 0.05 0.1 0.15 0.2 0.3 0.4 0.5
81/19 79/21 85/15 82/18 70/30 63/37 71/29 58/42
81/19 67/33 86/14 84/16 82/18 90/10 92/8 92/8
81/19 75/25 89/11 89/11 94/6 96/4 97/3 97/3
81/19 78/22 79/21 72/28 76/24 80/20 87/13 100/0
% 2223
296
45 40 35 30 25 20 15 10 5 0
B Al Ga In
0.0
0.1
0.2
0.3
0.4
0.5
x
Fig. 1. The content of 2223 phase as the function of concentration of additives (x),
(x ¼ 0:5). The result confirms the favourable influence of B2O3 (melting temperature 4501C) on the formation of Bi-2223 phase. XRD analysis did not identify any secondary phases. A small addition of Al2O3 and Ga2O3 (x ¼ 0:05) increased the volume of high-Tc 2223 phase, but the higher content of these additives stabilized the Bi-2212 phase. Indium had a positive influence on the formation of Bi-2223 phase up to x ¼ 0:15 and the with highest content of In, this phase disappears. A deeper analysis of the nature of the additives containing phases and the morphology of some samples (x ¼ 0:3 and 0.5) has been performed by scanning electron microscopy. It was not possible to detect boron in the samples due its low mass and low concentration. The phases surrounding
30.840
37.400
30.830
37.350 c (x 10-1 nm)
c (x 10-1 nm)
! D. Sykorov a! et al. / Physica B 321 (2002) 295–297
30.820 30.810 30.800 30.790
297
37.300 37.250 37.200 37.150 37.100
0
0.1
0.2 x
0.3
0.4 B Ga
0.5
0
Al In
0.1
0.2
x
0.3 B Ga
0.4 Al In
Fig. 2. The lattice parameter c for the 2212 phase.
Fig. 3. The lattice parameter c for the 2223 phase.
one phase region Bi-2223 have been identified [7]: Bi-2212, (Ca, Sr)14Cu24Ox=1424, (Ca, Sr)2CuO3=21 and CuO. These phases contained only a small amount (o1 at%) of additives. Some mixed oxides with a higher content of Al, Ga and In (4–20 at%) were found, for example: Bi7Sr13Ca3CuAl19O56.5, Bi2Sr5Ca7Cu4Ga4.5O27, Bi1.5Sr14Ca5Cu23In4.5O51. The experimental results did not detect the additives that took part in the structure of the superconducting phases. This is supported by little changes in the lattice parameters of the Bi-2212 and Bi-2223 phases (Figs. 2 and 3). All the samples where Bi was partially substituted by B and Al exhibited reproducible superconducting behaviour with Tc (determined from the inflection point of the resistance curve) in range 105–110 K. The samples with Ga had Tc B105 K up to x ¼ 0:2: When the content of Ga was higher, only the Bi-2212 phase was present. Indium-substituted samples had sharp transitions at 106–107 K up to x ¼ 0:4; and the sample with x ¼ 0:5 had Tc ¼ 74; 5 K (Bi-2212 phase). Samples with B (x ¼ 0:3), Al (x ¼ 0:05) and Ga
(x ¼ 0:15) had much higher values of critical current density when compared with samples without additives [8]. This observation resulted in our opinion that the secondary phases acting as pinning centres are probably formed.
Acknowledgements This work was supported by GACR under projects 104/99/1440 and 106/99/1441.
References [1] M. Takano, et al., Jpn. J. Appl. Phys. 27 (1988) L1041. [2] J.C. Grivel, R. Flukiger, . Superlattices Microstruct. 25 (1999) 527. [3] H. Nobumasa, et al., Jpn. J. Appl. Phys. 27 (1988) L864. [4] S. Sunshine, et al., Phys. Rev. B 38 (1988) 893. [5] L. Dimesso, et al., Physica C 227 (1994) 291. [6] M.E. Yakinci, et al., Physica C 235–240 (1994) 959. [7] P. Majewski, et al., J. Am. Ceram. Soc. 80 (1997) 1174. [8] O. Smr$ckov!a, D. S!ykorov!a, K. Rube$sov!a, P. Va$sek, in these Proceedings (MSM 2001), Physica B 321 (2002).