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Synthesis of high-purity RuSr2GdCu2O8 with semiconductivity
Physica C 382 (2002) 233–236 www.elsevier.com/locate/physc
Synthesis of high-purity RuSr2GdCu2O8 with semiconductivity Mingde Li a, Min Yu b, Zhongbing Wang a, Hongshun Yang b, Yuan Hu c, Zuyao Chen a,*, Zhiquan Li b, Liezhao Cao b a
c
Structure Research Laboratory and Department of Chemistry, University of Science and Technology of China, 230026 Hefei, Anhui, China b Department of Physics, University of Science and Technology of China, 230026 Hefei, Anhui, China State Key Fire Laboratory of China, University of Science and Technology of China, 230026 Hefei, Anhui, China Received 22 January 2001; received in revised form 25 March 2001
Abstract The synthesis of superconductor RuSr2 GdCu2 O8 by common solid-state reaction is always accompanied by the formation of small amounts of ferromagnetic SrRuO3 impurities. In this paper, we present a precursor method of pure RuSr2 GdCu2 O8 preparation. Pure precursor Sr2 GdRuO6 is synthesized by solid-state reaction in flowing O2 and water , b ¼ 5:802 A , c ¼ 8:206 A . RuSr2 GdCu2 O8 vapor. The precursor crystallizes in an orthorhombic structure, a ¼ 5:814 A prepared by this method is a high-purity RuSr2 GdCu2 O8 phase. Stoichiometric pure RuSr2 GdCu2 O8 is semiconductive. Ó 2002 Elsevier Science B.V. All rights reserved. PACS: 74.25.F; 74.25.H; 74.62.B Keywords: RuSr2 GdCu2 O8 ; Sr2 GdRuO6 ; SrRuO3 ; Water vapor
1. Introduction Two types of ruthenate–cuprate superconductors, RuSr2 LnCu2 O8 (Ru-1212) and RuSr2 (Ln, Ce)2 Cu2 O10 (Ru-1222) (Ln ¼ Sm, Eu, Gd) [1–4] had been synthesized. The synthesis of these phases by common solid-state reaction is always accompanied by the formation of ferromagnetic SrRuO3 impurities, which have a devastating influence on the superconductivity.
*
Corresponding author. Fax: +86-551-3631760. E-mail address: [email protected] (Z. Chen).
Recently, the material of Ru-1212 was found to display not only superconductivity, but coexisting ferromagnetism as well [5], and attracted a great deal of interest. RuSr2 GdCu2 O8 phase can be transformed into Sr2 GdRuO6 (Ru-211) and Cu2 O by sintering in flowing nitrogen. The conventional synthesis method [2] is calcining stoichiometric CuO, RuO2 , Gd2 O3 and SrCO3 to produce initial 1212 compound, then sintering it in flowing nitrogen and oxygen alternatively to reduce SrRuO3 by the transition between Ru-1212 and Ru-211 phases. But our effort to prepare pure 1212 samples by this method was not successful. In this paper, we present preparation of highpurity RuSr2 GdCu2 O8 compound from a precursor Sr2 GdRuO6 (Ru-211) that was synthesized by
0921-4534/02/$ - see front matter Ó 2002 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 1 - 4 5 3 4 ( 0 2 ) 0 1 1 3 7 - 1
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solid-state reaction in O2 and water vapor atmospheres. Some results about 211 and 1212 phases synthesized by this method are given.
2. Experimental The starting materials were high-purity oxides CuO (99.99%), RuO2 (99.99%), Gd2 O3 (Specpure, Johnson Matthey Chemicals) and strontium–carbonate SrCO3 (99.99%). The starting material of RuO2 contained crystal water, so it was baked at 400–500 °C for 5–6 h before weighing. Then it was taken out of furnace and weighed immediately. First, the powders of a stoichiometric RuO2 , Gd2 O3 , and SrCO3 mixture were calcined at 950 °C in flowing O2 and water vapor to synthesize the pure precursor Sr2 GdRuO6 . The flowing O2 was maintained during heating from room temperature to 600 °C, then, water vapor was added. The powders were calcined at 950 °C for 30 h in O2 and water vapor atmospheres. To prepare Ru-1212 samples, a stoichiometric mixture of pure Sr2 GdRuO6 and CuO was milled, pressed into pellets and sintered. X-ray diffraction (XRD) was carried out on a MXP18AHF diffractometer (CuKa1 radiation). Resistivity measurements were performed by a standard four-probe method.
3. Results and discussion As Ru-1212, the synthesis of Ru-211 in air or O2 is always accompanied by the formation of SrRuO3 impurities that could not be reduced by varying the synthesis temperature. But in flowing O2 and water vapor, a high-purity 211 compound was prepared from the starting materials RuO2 þ 1=2 ðGd2 O3 Þ þ 2ðSrCO3 ). The SrRuO3 phase could not be detected by XRD diffraction as shown in Fig. 1. The lattice parameters of the compound Sr2 , b ¼ GdRuO6 were refined to be a ¼ 5:814 A 5:802 A, c ¼ 8:206 A of orthorhombic symmetry. Similar compounds having the general formula A2 BRuO6 had been prepared [6–9]. All the materials adopt a perovskite-related structure with an
Fig. 1. The XRD spectrum for a Sr2 GdRuO6 (2 1 1) sample.
Fig. 2. Temperature dependence of the zero-field-cooled magnetization of Sr2 GdRuO6 .
alternative ordering of the B cations and Ru5þ on the octahedral site. Fig. 2 shows the zero-field-cooled magnetization measurement of 211 phase. The disappearance of peaks characteristic for the ferromagnetic transition of SrRuO3 at 160 K indicates that the 211 phase is pure without SrRuO3 . Its ferromagnetic transition at temperature about 50 K is in contrast with previous A2 BRuO6 compounds [6–9] that exhibit antiferromagnetism. Three samples were synthesized via the precursor route. Sample 1 was sintered at 930 °C in air for 24 h by one step, samples 2 and 3 were calcined
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Fig. 4. Temperature dependence of the resistivity of RuSr2 GdCu2 O8 (sample 1). Fig. 3. The XRD diagrams for RuSr2 GdCu2 O8 phase: (a) highpurity sample 1, (b) sample 2 with Sr2 GdRuO6 impurities.
in powders in O2 at 950 °C for 24 h first, then sintered in pellets at 1050 °C in 1 atm O2 for 24 h. Sample 1 was high-purity 1212 compound, and in samples 2 and 3 there were some Sr2 GdRuO6 and SrRuO3 impurities. Fig. 3 shows the powder diffraction diagrams of samples 1 and 2. The lattice parameters were re, c ¼ 11:51 A for sample 1 fined to be a ¼ 3:839 A , c ¼ 11:51 A for sample 2. The and a ¼ 3:832 A crystal structures are similar to that of MBa2 LaCu2 O8 (M ¼ Nb, Ta) and MA2 RECu2 O8 with M ¼ Nb or Ta, A ¼ Ba or Sr, and RE ¼ Pr or Sm [10–12]. Sample 1 is not superconductive although it is a high-purity phase as shown in Fig. 4. Annealing in O2 for long time or in high-oxygen pressure could not induce its superconductivity. Resistivity curve shows a typical semiconductive behavior. Fig. 5 shows resistivity measurements of samples 2 and 3. Resistivity curves exhibit ferromagnetic transition at 133 K as that reported [5] and superconductive transition from 24 to 30 K. But superconducting transition was not detected by magnetization measurement as shown in Fig. 6.
Fig. 5. Temperature dependence of the resistivity of RuSr2 GdCu2 O8 (samples 2 and 3).
In summary, pure Ru-1212 phase was synthesized successfully from a precursor of Sr2 GdRuO6 that was prepared by calcining in O2 and water vapor atmospheres. Stoichiometric RuSr2 GdCu2 O8 prepared by this method is semiconductive.
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References
Fig. 6. Temperature dependence of the zero-field-cooled magnetization of RuSr2 GdCu2 O8 .
Acknowledgement This work was supported by the Ministry of Science and Technology of China (NKBRSFG19990646).
[1] L. Bauerfeind, W. Widder, H.F. Braun, Physica C 254 (1995) 151. [2] L. Bauerfeind, W. Widder, H.F. Braun, J. Low Temp. Phys. 105 (1996) 1605. [3] T. Kaibin, Q. Yitai, Z. Yadun, Y. Li, C. Zuyao, Z. Yuheng, Physica C 259 (1996) 168. [4] A. Ono, Jpn. J. Appl. Phys. Part 2 34 (1995) L1121. [5] C. Bernhard et al., Phys. Rev. B 59 (1999) 14099. [6] P.D. Battle, J.B. Goodenough, R. Price, J. Solid State Chem. 46 (1983) 234. [7] P.D. Battle, W.J. Macklin, J. Solid State Chem. 52 (1984) 138. [8] P.D. Battle, W.J. Macklin, J. Solid State Chem. 54 (1984) 245. [9] P.D. Battle, C.W. Jones, J. Solid State Chem. 78 (1989) 108. [10] N. Murayama, E. Sudo, K. Kani, A. Tsuzuki, S. Kawakami, M. Awano, Y. Torii, Jpn. Appl. Phys. 27 (1988) L1623. [11] C. Greaves, P.R. Slater, Physica C 161 (1989) 245. [12] X.Z. Wang, B. Hellebrand, in: H. Kuzmany, M. Mehring, J. Fink (Eds.), Electronic Properties of High Tc Superconductors, Springer Series in Solid State Science, vol. 113, Springer-Verlag, New York/Berlin, 1993, p. 19.
Synthesis of high-purity RuSr2GdCu2O8 with semiconductivity Mingde Li a, Min Yu b, Zhongbing Wang a, Hongshun Yang b, Yuan Hu c, Zuyao Chen a,*, Zhiquan Li b, Liezhao Cao b a
c
Structure Research Laboratory and Department of Chemistry, University of Science and Technology of China, 230026 Hefei, Anhui, China b Department of Physics, University of Science and Technology of China, 230026 Hefei, Anhui, China State Key Fire Laboratory of China, University of Science and Technology of China, 230026 Hefei, Anhui, China Received 22 January 2001; received in revised form 25 March 2001
Abstract The synthesis of superconductor RuSr2 GdCu2 O8 by common solid-state reaction is always accompanied by the formation of small amounts of ferromagnetic SrRuO3 impurities. In this paper, we present a precursor method of pure RuSr2 GdCu2 O8 preparation. Pure precursor Sr2 GdRuO6 is synthesized by solid-state reaction in flowing O2 and water , b ¼ 5:802 A , c ¼ 8:206 A . RuSr2 GdCu2 O8 vapor. The precursor crystallizes in an orthorhombic structure, a ¼ 5:814 A prepared by this method is a high-purity RuSr2 GdCu2 O8 phase. Stoichiometric pure RuSr2 GdCu2 O8 is semiconductive. Ó 2002 Elsevier Science B.V. All rights reserved. PACS: 74.25.F; 74.25.H; 74.62.B Keywords: RuSr2 GdCu2 O8 ; Sr2 GdRuO6 ; SrRuO3 ; Water vapor
1. Introduction Two types of ruthenate–cuprate superconductors, RuSr2 LnCu2 O8 (Ru-1212) and RuSr2 (Ln, Ce)2 Cu2 O10 (Ru-1222) (Ln ¼ Sm, Eu, Gd) [1–4] had been synthesized. The synthesis of these phases by common solid-state reaction is always accompanied by the formation of ferromagnetic SrRuO3 impurities, which have a devastating influence on the superconductivity.
*
Corresponding author. Fax: +86-551-3631760. E-mail address: [email protected] (Z. Chen).
Recently, the material of Ru-1212 was found to display not only superconductivity, but coexisting ferromagnetism as well [5], and attracted a great deal of interest. RuSr2 GdCu2 O8 phase can be transformed into Sr2 GdRuO6 (Ru-211) and Cu2 O by sintering in flowing nitrogen. The conventional synthesis method [2] is calcining stoichiometric CuO, RuO2 , Gd2 O3 and SrCO3 to produce initial 1212 compound, then sintering it in flowing nitrogen and oxygen alternatively to reduce SrRuO3 by the transition between Ru-1212 and Ru-211 phases. But our effort to prepare pure 1212 samples by this method was not successful. In this paper, we present preparation of highpurity RuSr2 GdCu2 O8 compound from a precursor Sr2 GdRuO6 (Ru-211) that was synthesized by
0921-4534/02/$ - see front matter Ó 2002 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 1 - 4 5 3 4 ( 0 2 ) 0 1 1 3 7 - 1
234
M. Li et al. / Physica C 382 (2002) 233–236
solid-state reaction in O2 and water vapor atmospheres. Some results about 211 and 1212 phases synthesized by this method are given.
2. Experimental The starting materials were high-purity oxides CuO (99.99%), RuO2 (99.99%), Gd2 O3 (Specpure, Johnson Matthey Chemicals) and strontium–carbonate SrCO3 (99.99%). The starting material of RuO2 contained crystal water, so it was baked at 400–500 °C for 5–6 h before weighing. Then it was taken out of furnace and weighed immediately. First, the powders of a stoichiometric RuO2 , Gd2 O3 , and SrCO3 mixture were calcined at 950 °C in flowing O2 and water vapor to synthesize the pure precursor Sr2 GdRuO6 . The flowing O2 was maintained during heating from room temperature to 600 °C, then, water vapor was added. The powders were calcined at 950 °C for 30 h in O2 and water vapor atmospheres. To prepare Ru-1212 samples, a stoichiometric mixture of pure Sr2 GdRuO6 and CuO was milled, pressed into pellets and sintered. X-ray diffraction (XRD) was carried out on a MXP18AHF diffractometer (CuKa1 radiation). Resistivity measurements were performed by a standard four-probe method.
3. Results and discussion As Ru-1212, the synthesis of Ru-211 in air or O2 is always accompanied by the formation of SrRuO3 impurities that could not be reduced by varying the synthesis temperature. But in flowing O2 and water vapor, a high-purity 211 compound was prepared from the starting materials RuO2 þ 1=2 ðGd2 O3 Þ þ 2ðSrCO3 ). The SrRuO3 phase could not be detected by XRD diffraction as shown in Fig. 1. The lattice parameters of the compound Sr2 , b ¼ GdRuO6 were refined to be a ¼ 5:814 A 5:802 A, c ¼ 8:206 A of orthorhombic symmetry. Similar compounds having the general formula A2 BRuO6 had been prepared [6–9]. All the materials adopt a perovskite-related structure with an
Fig. 1. The XRD spectrum for a Sr2 GdRuO6 (2 1 1) sample.
Fig. 2. Temperature dependence of the zero-field-cooled magnetization of Sr2 GdRuO6 .
alternative ordering of the B cations and Ru5þ on the octahedral site. Fig. 2 shows the zero-field-cooled magnetization measurement of 211 phase. The disappearance of peaks characteristic for the ferromagnetic transition of SrRuO3 at 160 K indicates that the 211 phase is pure without SrRuO3 . Its ferromagnetic transition at temperature about 50 K is in contrast with previous A2 BRuO6 compounds [6–9] that exhibit antiferromagnetism. Three samples were synthesized via the precursor route. Sample 1 was sintered at 930 °C in air for 24 h by one step, samples 2 and 3 were calcined
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Fig. 4. Temperature dependence of the resistivity of RuSr2 GdCu2 O8 (sample 1). Fig. 3. The XRD diagrams for RuSr2 GdCu2 O8 phase: (a) highpurity sample 1, (b) sample 2 with Sr2 GdRuO6 impurities.
in powders in O2 at 950 °C for 24 h first, then sintered in pellets at 1050 °C in 1 atm O2 for 24 h. Sample 1 was high-purity 1212 compound, and in samples 2 and 3 there were some Sr2 GdRuO6 and SrRuO3 impurities. Fig. 3 shows the powder diffraction diagrams of samples 1 and 2. The lattice parameters were re, c ¼ 11:51 A for sample 1 fined to be a ¼ 3:839 A , c ¼ 11:51 A for sample 2. The and a ¼ 3:832 A crystal structures are similar to that of MBa2 LaCu2 O8 (M ¼ Nb, Ta) and MA2 RECu2 O8 with M ¼ Nb or Ta, A ¼ Ba or Sr, and RE ¼ Pr or Sm [10–12]. Sample 1 is not superconductive although it is a high-purity phase as shown in Fig. 4. Annealing in O2 for long time or in high-oxygen pressure could not induce its superconductivity. Resistivity curve shows a typical semiconductive behavior. Fig. 5 shows resistivity measurements of samples 2 and 3. Resistivity curves exhibit ferromagnetic transition at 133 K as that reported [5] and superconductive transition from 24 to 30 K. But superconducting transition was not detected by magnetization measurement as shown in Fig. 6.
Fig. 5. Temperature dependence of the resistivity of RuSr2 GdCu2 O8 (samples 2 and 3).
In summary, pure Ru-1212 phase was synthesized successfully from a precursor of Sr2 GdRuO6 that was prepared by calcining in O2 and water vapor atmospheres. Stoichiometric RuSr2 GdCu2 O8 prepared by this method is semiconductive.
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References
Fig. 6. Temperature dependence of the zero-field-cooled magnetization of RuSr2 GdCu2 O8 .
Acknowledgement This work was supported by the Ministry of Science and Technology of China (NKBRSFG19990646).
[1] L. Bauerfeind, W. Widder, H.F. Braun, Physica C 254 (1995) 151. [2] L. Bauerfeind, W. Widder, H.F. Braun, J. Low Temp. Phys. 105 (1996) 1605. [3] T. Kaibin, Q. Yitai, Z. Yadun, Y. Li, C. Zuyao, Z. Yuheng, Physica C 259 (1996) 168. [4] A. Ono, Jpn. J. Appl. Phys. Part 2 34 (1995) L1121. [5] C. Bernhard et al., Phys. Rev. B 59 (1999) 14099. [6] P.D. Battle, J.B. Goodenough, R. Price, J. Solid State Chem. 46 (1983) 234. [7] P.D. Battle, W.J. Macklin, J. Solid State Chem. 52 (1984) 138. [8] P.D. Battle, W.J. Macklin, J. Solid State Chem. 54 (1984) 245. [9] P.D. Battle, C.W. Jones, J. Solid State Chem. 78 (1989) 108. [10] N. Murayama, E. Sudo, K. Kani, A. Tsuzuki, S. Kawakami, M. Awano, Y. Torii, Jpn. Appl. Phys. 27 (1988) L1623. [11] C. Greaves, P.R. Slater, Physica C 161 (1989) 245. [12] X.Z. Wang, B. Hellebrand, in: H. Kuzmany, M. Mehring, J. Fink (Eds.), Electronic Properties of High Tc Superconductors, Springer Series in Solid State Science, vol. 113, Springer-Verlag, New York/Berlin, 1993, p. 19.