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Iron mixed-valence compounds, BaSm(Cu0.5+xFe0.5−x)2O5+δ
Physica C 338 Ž2000. 121–125 www.elsevier.nlrlocaterphysc
Iron mixed-valence compounds, BaSm žCu 0.5qx Fe 0.5yx / 2 O5qd I: Synthesis and chemical characterization J. Nakamura a,b, J. Linden ´ a,c , H. Suematsu a, M. Karppinen a,d , H. Yamauchi a,b,) b
a Materials and Structures Laboratory, Tokyo Institute of Technology, Yokohama 226-8503, Japan Department of InnoÕatiÕe and Engineered Materials, Interdisciplinary Graduate School, Tokyo Institute of Technology, Yokohama 226-8502, Japan c ˚ Akademi UniÕersity, FIN-20500 Turku, Finland Department of Physics, Abo d Laboratory of Inorganic and Analytical Chemistry, Helsinki UniÕersity of Technology, FIN-02015 Espoo, Finland
Abstract Oxygen-deficient BaSmŽCu 0.5qx Fe 0.5yx . 2 O5q d Ž x s y0.5, y0.45, y0.4, y0.1 and 0.0. double-perovskite samples have been successfully obtained by means of a novel synthesis technique utilizing an FerFeO getter encapsulated together with the starting material mixture in an evacuated silica-glass tube. The reducing conditions during the synthesis correspond to an oxygen partial pressure of ; 7.6 = 10y16 atm. From X-ray diffraction ŽXRD., transmission electron micrographs ŽTEM. and energy-dispersive X-ray ŽEDX. analyses, the samples have been confirmed to be of essentially single phase. By post-annealing the as-synthesized samples under O 2 or H 2rAr mixed gas, the amount of excess oxygen was controlled. Approaching d f 0 required prolonged annealing periods under reducing conditions. Samples having y0.4 - x - y0.1 did not form as a single-phase material under the present synthesis conditions. q 2000 Elsevier Science B.V. All rights reserved. Keywords: FerFeO getter; BaSmŽCu 0.5qx Fe 0.5yx . 2 O5q d ; XRD
1. Introduction Oxygen-deficient double-perovskite compounds, BaRT2 O5q d ŽR s rare earth element; T s transition metal., can be categorized as n s 2 phases of the 01Ž n y 1. n homologous series if the same classifica-
)
Corresponding author. Materials and Structures Laboratory, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 226-8503, Japan. Tel.: q81-45-924-5315; fax: q81-45-9245365. E-mail address: [email protected] ŽH. Yamauchi..
tion system as that developed for the multi-layered superconductive copper-oxide structures is applied w1x. The first BaRT2 O5q d compound with the 0112 structure ŽFig. 1. was BaYCuFeO5 isolated by ErRakho et al. w2x in 1988. Later, it was found that the 0112 structure is adopted by the BaYŽCo 1y xCu x . 2 O5q d Ž0.15 F x F 0.5. w3–5x and BaYŽCo 0.5Cu 0.5yx Fe x . 2 O5q d Ž0.15 F x F 0.3. w6x systems as well, but samples with the transition-metal site occupied by one single element were difficult to synthesize. In fact, an early study on the mutual solid solubility of Cu and Fe at the transition-metal site in the BaYŽCu 0.5qx Fe 0.5yx . 2 O5q d system indicated a very narrow interval around the optimum of equal
0921-4534r00r$ - see front matter q 2000 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 1 - 4 5 3 4 Ž 0 0 . 0 0 2 1 3 - 6
122
J. Nakamura et al.r Physica C 338 (2000) 121–125
an appropriate metalrmetal-oxide getter is reported for the BaSmFe 2 O5q d phase. A further goal of the present work was to find the ways to synthesize BaSmŽCu 0.5qx Fe 0.5yx . 2 O5q d samples with a controlled oxygen content in the range of y0.5 F x F 0.0.
2. Experimental
Fig. 1. The ‘‘0112’’ structure of BaRŽCu 0.5qx Fe 0.5yx . 2 O5q d .
amounts of Fe and Cu w7x. Thus far, the highest Cu concentration achieved was 70%, i.e. x s 0.2, obtained through high-pressure heat treatment w8x. Recently, however, the Cu-free BaSmFe 2 O5q d phase was successfully synthesized under low oxygen partial pressures w9x. In the reduced samples of the BaSmFe 2 O5q d phase Ž d f 0., a valence-fluctuation state of iron, formally denoted as Fe 2.5q was furthermore observed by means of Mossbauer spectroscopy ¨ w10x. In the present contribution, a novel encapsulation synthesis technique in which the oxygen partial pressure inside the synthesis ampoule is controlled with
Bulk BaSmŽCu 0.5qx Fe 0.5yx . 2 O5q d Žy0.5 F x F 0.0. materials were prepared from high-purity powders of BaCO 3 , Sm 2 O 3 , Fe 2 O 3 and CuO. Appropriate mixtures of the starting materials were first calcined twice in O 2 at 9008C for 15 h with an intermediate grinding. The calcined powders were then pelletted, and for the compositions with y0.5 F x F y0.3, sintered encapsulated in evacuated silica-glass tubes containing the sample pellets together with Fe grains Ž99.9% up, under 10 mesh. as a getter ŽFig. 2.. The heat treatment was carried out at 9858C for 40 h. Under these conditions, the oxygen partial pressure is expected to equilibrate at 7.6 = 10y1 6 atm due to the redox couple of FerFeO w11x. After the heat treatment, the silica-glass tube was quenched in air in about 1 h down to room temperature. Also, other synthesis conditions were tried, see Table 1. During storage, the synthesized Fe-rich samples were kept in an inert N2 atmosphere to avoid spontaneous oxidation. The samples with y0.1 F x F 0.0 were sintered at 9858C for 40 h in air or in a flowing gas
Fig. 2. Cross-section of the ampoule used during the present encapsulation synthesis.
J. Nakamura et al.r Physica C 338 (2000) 121–125
123
Table 1 Summary of the synthesis conditions applied in the present work for the BaSmŽCu 0.5qx Fe 0.5yx . 2 O5q d samples. In each case, the synthesis time was 40 h Synthesis temperature Ž8C. Getterrgas
985
985
1035
985
985
985
985
985
Fe
Fe
Fe
Co
Ni
Flowing 0.1% O 2
Flowing Ar
Air
pO 2 Žatm.
7.6 = 10y16
Furnace cooling lower than 7.6 = 10y1 6
6.2 = 10y15
1.0 = 10y12
1.3 = 10y10
` ` ` =
n n n
n n
n n
n n
x y0.5 y0.45 y0.4 y0.3 y0.1 0
´
= = n
= n n
` `
`: single-phase double perovskite, n: double perovskiteq impurity phaseŽs., =: no double perovskite.
mixture of ; 0.1% O 2rAr. The same gas mixture was used for oxidizing the y0.5 F x F y0.4 samples at 9008C for 5 h in a thermobalance ŽMAC Science TGrDTA 2000S.. Furthermore, using the thermobalance, the oxygen content of the as-synthesized materials was varied in a controlled manner under a 5% H 2rAr gas mixture. The synthesized samples were checked for phase-purity and lattice parameters by X-ray diffraction ŽXRD; MAC Science M18XHF 22 ; CuK a radiation.. The crystal structures and the cation compositions were investigated by electron diffraction ŽED., high-resolution transmission-electron microscopy ŽHRTEM; Hitachi H-9000. and energy-dispersive X-ray ŽEDX. analysis ŽKevex-Sigma..
rized in Table 1. This is in line with the results of previously reported solid-solubility studies w7x. How-
3. Results and discussion According to the XRD data shown in Fig. 3, the as-synthesized samples corresponding to x s y0.5, y0.45, y0.4, y0.1 and 0.0 were single phase. Also, high-resolution transmission electron micrographs ŽTEM. ŽFig. 4a., ED patterns ŽFig. 4b. and EDX analysis data indicate the double-perovskite structure for these samples. For x values in the interval y0.4 - x - y0.1, a single-phase material was not obtained, even though efforts were made to control the oxygen partial pressure by means of changing the metal getter or temperature, as summa-
Fig. 3. XRD patterns for the as-synthesized Ža. BaSmFe 2 O5q d , Žb. BaSmŽCu 0.05 Fe 0.95 . 2 O5q d , Žc. BaSmŽCu 0.1 Fe 0.9 . 2 O5q d , Žd. BaSmŽCu 0.4 Fe 0.6 . 2 O5q d and Že. BaSmŽCu 0.5 Fe 0.5 . 2 O5q d samples.
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J. Nakamura et al.r Physica C 338 (2000) 121–125
Fig. 4. Ža. HRTEM image and Žb. ED pattern for the as-synthesized BaSmFe 2 O5q d sample.
ever, since the Cu and Fe atoms have been found to populate randomly the transition-metal site w12,13x, one would expect to achieve larger solubility limits, provided the optimal thermodynamic conditions during the synthesis were found. In the Cu-free BaSmFe 2 O5q d sample, the oxygen stoichiometry was easily varied within 0 - d - 0.7 by post-annealing treatments in 0.1% O 2rAr and 5% H 2rAr atmospheres, as estimated from the corresponding TG data. The most reduced samples were obtained by annealing in 5% H 2rAr at 6008C for 5 h. With increasing oxygen content, the a-axis parameter decreased, while both the c-axis parameter and the unit cell volume increased ŽFig. 5.. Although TG analysis of the x s y0.45 and y0.4 samples indicated a completed oxygen loss in 5% H 2rAr at 6008C, the Mossbauer spectra reported for the same ¨ samples in Ref. w14x show a clear presence of excess oxygen Ž d f 0.1.. In fact, both the overall amount of Fe 2.5qrFe 2q and the amount of six-coordinated Fe 3q in the Mossbauer spectra give mutually consistent ¨ non-zero d values for all the reduced BaSmŽCu 0.5qx Fe 0.5yx . 2 O5q d samples. In order to explore the problem with excess oxygen, the BaSmŽCu 0.1 Fe 0.9 . 2 O5q d sample was annealed at various conditions in the reducing 5% H 2rAr atmosphere. According to the analysis of the Mossbauer spectra, ¨ the lowest oxygen content of d s 0.037 was obtained for the sample annealed at 6808C for 48 h. The
slightly Cu-doped x s y0.45 and y0.4 samples were very prone to degradation upon oxidizing them in air. Thus, oxygen loading was performed under a low oxygen partial pressure. Finally, an interesting observation is that the response of the c-axis parameter to increasing d changes gradually with increasing Cu concentration. That is, even though the c axis is expanded with increasing d in Fe-rich samples, it is quite insensitive to d in heavily Cu-doped samples.
Fig. 5. Lattice parameters, a and c, and the unit cell volume of the BaSmFe 2 O5q d phase as a function of excess oxygen, d .
J. Nakamura et al.r Physica C 338 (2000) 121–125
125
4. Conclusions
References
A novel encapsulation synthesis technique utilizing FerFeO as a getter was developed for synthesizing the BaSmFe 2 O5q d double-perovskite phase. Also, Cu-doped BaSmŽCu 0.5qx Fe 0.5yx . 2 O5q d samples with x s y0.45, y0.4, y0.1, and 0.0 were successfully obtained; whereas, attempts to synthesize samples with y0.4 - x - y0.1 failed. The oxygen contents of the samples could be tuned in the interval 0 - d - 0.7, by reducing or oxidizing the samples in 5% H 2rAr or 0.1% O 2rAr atmospheres, respectively.
w1x H. Yamauchi, M. Karppinen, S. Tanaka, Physica C 263 Ž1996. 146. w2x L. Er-Rakho, C. Michel, Ph. Lacorre, B. Raveau, J. Solid State Chem. 73 Ž1988. 531. w3x L. Barbey, N. Nguyen, V. Caignaert, M. Hervieu, B. Raveau, Mater. Res. Bull. 27 Ž1992. 295. w4x L. Barbey, N. Nguyen, V. Caignaert, F. Studer, B. Raveau, J. Solid State Chem. 112 Ž1994. 148. w5x Q. Huang, P. Karen, V.L. Karen, A. Kjekshus, J.W. Lynn, A.D. Mighell, I. Natali Sora, N. Rosov, A. Santoro, J. Solid State Chem. 108 Ž1995. 80. w6x L. Barbey, N. Nguyen, A. Ducouret, V. Caignaert, J.M. Greneche, B. Raveau, J. Solid State Chem. 115 Ž1995. 514. ` w7x P. Karen, P.H. Andersen, A. Kjekshus, J. Solid State Chem. 101 Ž1992. 48. w8x M. Nagase, J. Linden, ´ H. Suematsu, M. Karppinen, H. Yamauchi, Phys. Rev. B 59 Ž1999. 1377. w9x P. Karen, P.M. Woodward, J. Mater. Chem. 9 Ž1999. 789. w10x J. Linden, ´ P. Karen, A. Kjekshus, J. Miettinen, T. Pietari, M. Karppinen, Phys. Rev. B 60 Ž1999. 15251. w11x F.D. Richardson, J.H.E. Jeffes, J. Iron Steel Inst. 160 Ž1948. 261. w12x H. Suematsu, M. Nagase, Y. Tomokiyo, M. Karppinen, H. Yamauchi, in: N. Koshizuka, S. Tajima ŽEds.., Advances in Superconductivity XI Springer, Tokyo, 1998, pp. 389–392. w13x J. Linden, ´ M. Kochi, K. Lehmus, T. Pietari, M. Karppinen, H. Yamauchi, unpublished. w14x J. Linden, ´ J. Nakamura, T. Pietari, T. Taniyama, M. Karppinen, H. Yamauchi, Physica C 338 Ž2000. these proceedings.
Acknowledgements Dr. S.R. Lee is acknowledged for useful advice during the course of this work. One of the authors ŽJ.L.. acknowledges the kind support from the Japan Society for the Promotion of Science. The present work has been supported by a Grant-in-Aid for Scientific Research Žcontract No. 11305002. from The Ministry of Education, Science and Culture of Japan, and also by an International Collaborative Research Project Grant-1999 of the Materials and Structures Laboratory, Tokyo Institute of Technology.
Iron mixed-valence compounds, BaSm žCu 0.5qx Fe 0.5yx / 2 O5qd I: Synthesis and chemical characterization J. Nakamura a,b, J. Linden ´ a,c , H. Suematsu a, M. Karppinen a,d , H. Yamauchi a,b,) b
a Materials and Structures Laboratory, Tokyo Institute of Technology, Yokohama 226-8503, Japan Department of InnoÕatiÕe and Engineered Materials, Interdisciplinary Graduate School, Tokyo Institute of Technology, Yokohama 226-8502, Japan c ˚ Akademi UniÕersity, FIN-20500 Turku, Finland Department of Physics, Abo d Laboratory of Inorganic and Analytical Chemistry, Helsinki UniÕersity of Technology, FIN-02015 Espoo, Finland
Abstract Oxygen-deficient BaSmŽCu 0.5qx Fe 0.5yx . 2 O5q d Ž x s y0.5, y0.45, y0.4, y0.1 and 0.0. double-perovskite samples have been successfully obtained by means of a novel synthesis technique utilizing an FerFeO getter encapsulated together with the starting material mixture in an evacuated silica-glass tube. The reducing conditions during the synthesis correspond to an oxygen partial pressure of ; 7.6 = 10y16 atm. From X-ray diffraction ŽXRD., transmission electron micrographs ŽTEM. and energy-dispersive X-ray ŽEDX. analyses, the samples have been confirmed to be of essentially single phase. By post-annealing the as-synthesized samples under O 2 or H 2rAr mixed gas, the amount of excess oxygen was controlled. Approaching d f 0 required prolonged annealing periods under reducing conditions. Samples having y0.4 - x - y0.1 did not form as a single-phase material under the present synthesis conditions. q 2000 Elsevier Science B.V. All rights reserved. Keywords: FerFeO getter; BaSmŽCu 0.5qx Fe 0.5yx . 2 O5q d ; XRD
1. Introduction Oxygen-deficient double-perovskite compounds, BaRT2 O5q d ŽR s rare earth element; T s transition metal., can be categorized as n s 2 phases of the 01Ž n y 1. n homologous series if the same classifica-
)
Corresponding author. Materials and Structures Laboratory, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 226-8503, Japan. Tel.: q81-45-924-5315; fax: q81-45-9245365. E-mail address: [email protected] ŽH. Yamauchi..
tion system as that developed for the multi-layered superconductive copper-oxide structures is applied w1x. The first BaRT2 O5q d compound with the 0112 structure ŽFig. 1. was BaYCuFeO5 isolated by ErRakho et al. w2x in 1988. Later, it was found that the 0112 structure is adopted by the BaYŽCo 1y xCu x . 2 O5q d Ž0.15 F x F 0.5. w3–5x and BaYŽCo 0.5Cu 0.5yx Fe x . 2 O5q d Ž0.15 F x F 0.3. w6x systems as well, but samples with the transition-metal site occupied by one single element were difficult to synthesize. In fact, an early study on the mutual solid solubility of Cu and Fe at the transition-metal site in the BaYŽCu 0.5qx Fe 0.5yx . 2 O5q d system indicated a very narrow interval around the optimum of equal
0921-4534r00r$ - see front matter q 2000 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 1 - 4 5 3 4 Ž 0 0 . 0 0 2 1 3 - 6
122
J. Nakamura et al.r Physica C 338 (2000) 121–125
an appropriate metalrmetal-oxide getter is reported for the BaSmFe 2 O5q d phase. A further goal of the present work was to find the ways to synthesize BaSmŽCu 0.5qx Fe 0.5yx . 2 O5q d samples with a controlled oxygen content in the range of y0.5 F x F 0.0.
2. Experimental
Fig. 1. The ‘‘0112’’ structure of BaRŽCu 0.5qx Fe 0.5yx . 2 O5q d .
amounts of Fe and Cu w7x. Thus far, the highest Cu concentration achieved was 70%, i.e. x s 0.2, obtained through high-pressure heat treatment w8x. Recently, however, the Cu-free BaSmFe 2 O5q d phase was successfully synthesized under low oxygen partial pressures w9x. In the reduced samples of the BaSmFe 2 O5q d phase Ž d f 0., a valence-fluctuation state of iron, formally denoted as Fe 2.5q was furthermore observed by means of Mossbauer spectroscopy ¨ w10x. In the present contribution, a novel encapsulation synthesis technique in which the oxygen partial pressure inside the synthesis ampoule is controlled with
Bulk BaSmŽCu 0.5qx Fe 0.5yx . 2 O5q d Žy0.5 F x F 0.0. materials were prepared from high-purity powders of BaCO 3 , Sm 2 O 3 , Fe 2 O 3 and CuO. Appropriate mixtures of the starting materials were first calcined twice in O 2 at 9008C for 15 h with an intermediate grinding. The calcined powders were then pelletted, and for the compositions with y0.5 F x F y0.3, sintered encapsulated in evacuated silica-glass tubes containing the sample pellets together with Fe grains Ž99.9% up, under 10 mesh. as a getter ŽFig. 2.. The heat treatment was carried out at 9858C for 40 h. Under these conditions, the oxygen partial pressure is expected to equilibrate at 7.6 = 10y1 6 atm due to the redox couple of FerFeO w11x. After the heat treatment, the silica-glass tube was quenched in air in about 1 h down to room temperature. Also, other synthesis conditions were tried, see Table 1. During storage, the synthesized Fe-rich samples were kept in an inert N2 atmosphere to avoid spontaneous oxidation. The samples with y0.1 F x F 0.0 were sintered at 9858C for 40 h in air or in a flowing gas
Fig. 2. Cross-section of the ampoule used during the present encapsulation synthesis.
J. Nakamura et al.r Physica C 338 (2000) 121–125
123
Table 1 Summary of the synthesis conditions applied in the present work for the BaSmŽCu 0.5qx Fe 0.5yx . 2 O5q d samples. In each case, the synthesis time was 40 h Synthesis temperature Ž8C. Getterrgas
985
985
1035
985
985
985
985
985
Fe
Fe
Fe
Co
Ni
Flowing 0.1% O 2
Flowing Ar
Air
pO 2 Žatm.
7.6 = 10y16
Furnace cooling lower than 7.6 = 10y1 6
6.2 = 10y15
1.0 = 10y12
1.3 = 10y10
` ` ` =
n n n
n n
n n
n n
x y0.5 y0.45 y0.4 y0.3 y0.1 0
´
= = n
= n n
` `
`: single-phase double perovskite, n: double perovskiteq impurity phaseŽs., =: no double perovskite.
mixture of ; 0.1% O 2rAr. The same gas mixture was used for oxidizing the y0.5 F x F y0.4 samples at 9008C for 5 h in a thermobalance ŽMAC Science TGrDTA 2000S.. Furthermore, using the thermobalance, the oxygen content of the as-synthesized materials was varied in a controlled manner under a 5% H 2rAr gas mixture. The synthesized samples were checked for phase-purity and lattice parameters by X-ray diffraction ŽXRD; MAC Science M18XHF 22 ; CuK a radiation.. The crystal structures and the cation compositions were investigated by electron diffraction ŽED., high-resolution transmission-electron microscopy ŽHRTEM; Hitachi H-9000. and energy-dispersive X-ray ŽEDX. analysis ŽKevex-Sigma..
rized in Table 1. This is in line with the results of previously reported solid-solubility studies w7x. How-
3. Results and discussion According to the XRD data shown in Fig. 3, the as-synthesized samples corresponding to x s y0.5, y0.45, y0.4, y0.1 and 0.0 were single phase. Also, high-resolution transmission electron micrographs ŽTEM. ŽFig. 4a., ED patterns ŽFig. 4b. and EDX analysis data indicate the double-perovskite structure for these samples. For x values in the interval y0.4 - x - y0.1, a single-phase material was not obtained, even though efforts were made to control the oxygen partial pressure by means of changing the metal getter or temperature, as summa-
Fig. 3. XRD patterns for the as-synthesized Ža. BaSmFe 2 O5q d , Žb. BaSmŽCu 0.05 Fe 0.95 . 2 O5q d , Žc. BaSmŽCu 0.1 Fe 0.9 . 2 O5q d , Žd. BaSmŽCu 0.4 Fe 0.6 . 2 O5q d and Že. BaSmŽCu 0.5 Fe 0.5 . 2 O5q d samples.
124
J. Nakamura et al.r Physica C 338 (2000) 121–125
Fig. 4. Ža. HRTEM image and Žb. ED pattern for the as-synthesized BaSmFe 2 O5q d sample.
ever, since the Cu and Fe atoms have been found to populate randomly the transition-metal site w12,13x, one would expect to achieve larger solubility limits, provided the optimal thermodynamic conditions during the synthesis were found. In the Cu-free BaSmFe 2 O5q d sample, the oxygen stoichiometry was easily varied within 0 - d - 0.7 by post-annealing treatments in 0.1% O 2rAr and 5% H 2rAr atmospheres, as estimated from the corresponding TG data. The most reduced samples were obtained by annealing in 5% H 2rAr at 6008C for 5 h. With increasing oxygen content, the a-axis parameter decreased, while both the c-axis parameter and the unit cell volume increased ŽFig. 5.. Although TG analysis of the x s y0.45 and y0.4 samples indicated a completed oxygen loss in 5% H 2rAr at 6008C, the Mossbauer spectra reported for the same ¨ samples in Ref. w14x show a clear presence of excess oxygen Ž d f 0.1.. In fact, both the overall amount of Fe 2.5qrFe 2q and the amount of six-coordinated Fe 3q in the Mossbauer spectra give mutually consistent ¨ non-zero d values for all the reduced BaSmŽCu 0.5qx Fe 0.5yx . 2 O5q d samples. In order to explore the problem with excess oxygen, the BaSmŽCu 0.1 Fe 0.9 . 2 O5q d sample was annealed at various conditions in the reducing 5% H 2rAr atmosphere. According to the analysis of the Mossbauer spectra, ¨ the lowest oxygen content of d s 0.037 was obtained for the sample annealed at 6808C for 48 h. The
slightly Cu-doped x s y0.45 and y0.4 samples were very prone to degradation upon oxidizing them in air. Thus, oxygen loading was performed under a low oxygen partial pressure. Finally, an interesting observation is that the response of the c-axis parameter to increasing d changes gradually with increasing Cu concentration. That is, even though the c axis is expanded with increasing d in Fe-rich samples, it is quite insensitive to d in heavily Cu-doped samples.
Fig. 5. Lattice parameters, a and c, and the unit cell volume of the BaSmFe 2 O5q d phase as a function of excess oxygen, d .
J. Nakamura et al.r Physica C 338 (2000) 121–125
125
4. Conclusions
References
A novel encapsulation synthesis technique utilizing FerFeO as a getter was developed for synthesizing the BaSmFe 2 O5q d double-perovskite phase. Also, Cu-doped BaSmŽCu 0.5qx Fe 0.5yx . 2 O5q d samples with x s y0.45, y0.4, y0.1, and 0.0 were successfully obtained; whereas, attempts to synthesize samples with y0.4 - x - y0.1 failed. The oxygen contents of the samples could be tuned in the interval 0 - d - 0.7, by reducing or oxidizing the samples in 5% H 2rAr or 0.1% O 2rAr atmospheres, respectively.
w1x H. Yamauchi, M. Karppinen, S. Tanaka, Physica C 263 Ž1996. 146. w2x L. Er-Rakho, C. Michel, Ph. Lacorre, B. Raveau, J. Solid State Chem. 73 Ž1988. 531. w3x L. Barbey, N. Nguyen, V. Caignaert, M. Hervieu, B. Raveau, Mater. Res. Bull. 27 Ž1992. 295. w4x L. Barbey, N. Nguyen, V. Caignaert, F. Studer, B. Raveau, J. Solid State Chem. 112 Ž1994. 148. w5x Q. Huang, P. Karen, V.L. Karen, A. Kjekshus, J.W. Lynn, A.D. Mighell, I. Natali Sora, N. Rosov, A. Santoro, J. Solid State Chem. 108 Ž1995. 80. w6x L. Barbey, N. Nguyen, A. Ducouret, V. Caignaert, J.M. Greneche, B. Raveau, J. Solid State Chem. 115 Ž1995. 514. ` w7x P. Karen, P.H. Andersen, A. Kjekshus, J. Solid State Chem. 101 Ž1992. 48. w8x M. Nagase, J. Linden, ´ H. Suematsu, M. Karppinen, H. Yamauchi, Phys. Rev. B 59 Ž1999. 1377. w9x P. Karen, P.M. Woodward, J. Mater. Chem. 9 Ž1999. 789. w10x J. Linden, ´ P. Karen, A. Kjekshus, J. Miettinen, T. Pietari, M. Karppinen, Phys. Rev. B 60 Ž1999. 15251. w11x F.D. Richardson, J.H.E. Jeffes, J. Iron Steel Inst. 160 Ž1948. 261. w12x H. Suematsu, M. Nagase, Y. Tomokiyo, M. Karppinen, H. Yamauchi, in: N. Koshizuka, S. Tajima ŽEds.., Advances in Superconductivity XI Springer, Tokyo, 1998, pp. 389–392. w13x J. Linden, ´ M. Kochi, K. Lehmus, T. Pietari, M. Karppinen, H. Yamauchi, unpublished. w14x J. Linden, ´ J. Nakamura, T. Pietari, T. Taniyama, M. Karppinen, H. Yamauchi, Physica C 338 Ž2000. these proceedings.
Acknowledgements Dr. S.R. Lee is acknowledged for useful advice during the course of this work. One of the authors ŽJ.L.. acknowledges the kind support from the Japan Society for the Promotion of Science. The present work has been supported by a Grant-in-Aid for Scientific Research Žcontract No. 11305002. from The Ministry of Education, Science and Culture of Japan, and also by an International Collaborative Research Project Grant-1999 of the Materials and Structures Laboratory, Tokyo Institute of Technology.