M. Shimada
Osaka University
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Materials Research Bulletin | 1978
Yasuo Takeda; Shigeharu Naka; M. Takano; Teruya Shinjo; Toshio Takada; M. Shimada
Abstract Stoichiometric CaFeO 3 was prepared and was characterized by crystallographic, magnetic and electrical measurements. A slight tetragonal distortion from the ideal cubic perovskite structure was found. The tetramolecular unit cell has a = 5.325 (3) A and c = 7.579 (5) A. The susceptibility showed a maximum at about 115 K and the temperature dependence of electrical resistivity changed from metallic to semiconductive in the vicinity of the magnetic transition temperature. These indicate a phase transition from the metallic-paramagnetic (the high-temperature phase) to the semiconductive-antiferromagnetic phase. The Mossbauer spectra indicated that a charge disproportionation 2Fe 4+ → Fe 3+ + Fe 5+ associates with the transition.
Journal of Solid State Chemistry | 1979
H. Taguchi; M. Shimada; M. Koizumi
Abstract The cubic perovskite SrCoO 3−δ (0.05 ⩽ δ ⩽ 0.26) was prepared under high oxygen pressures of 50–2600 bars, and its crystallographic and magnetic properties were examined. From the results, it was found that oxygen deficiency strongly influences the unit-cell parameters and the Curie temperatures. The unit-cell parameter a 0 = 3.836 A and the Curie temperature 222°K for SrCoO 3 were determined.
Materials Research Bulletin | 1978
H. Taguchi; M. Shimada; M. Koizumi
The cubic perovskites La1−xSrxCoO3 (0.5 ≦ x ≦ 1.0) were prepared under high oxygen pressures. From the results of the magnetic measurements, it is found that Co3+ ions are in a high spin state and Co4+ ions in a low spin state. The superexchange interaction for Co3+-O-Co4+ is the strongest of all superexchange interactions in this system.
Materials Research Bulletin | 1980
H. Taguchi; M. Shimada; M. Koizumi
The electrical resistivity of ferromagnetic SrCoO3−δ (0 <δ <0.5) was measured in the temperature range from 77 to 300 K. All samples were good conductors and showed metallic behavior. The magnetic transition was independent of the electrical conductivity in SrCoO3−δ. The logarithm specific electrical resistivities (logρ) at 80 K and 300 K monotonously decreased with increasing the oxygen deficiency, and this result was explained by the itinerant-electron model.
Journal of Solid State Chemistry | 1976
H. Taguchi; M. Shimada; Fumikazu Kanamaru; M. Koizumi; Y. Takeda
Abstract The compounds in the systems of BaCo 1− x Mn x O 3 (0 ≦ x ≦ 1) and SrCo 1− x Mn x O 3 (0 ≦ x ≦ 1) were prepared at an oxygen pressure of 1400 bars. The former had a two-layer hexagonal structure and that of the latter was cubic perovskite type. From the variation of the unit-cell parameters and of the magnetic properties, it is found that the Co 4+ ions change from the low-spin to the high-spin state. In the system of SrCo 1− x Mn x O 3 , the change of magnetic property from ferromagnet to antiferromagnet is related to the spin state of Co 4+ ions located at the octahedral sites.
Journal of Solid State Chemistry | 1982
H. Taguchi; M. Shimada; M. Koizumi
Abstract The perovskite (La1−xCax)CoO3 (0 ≦ x ≦ 0.6) was prepared under high oxygen pressures. The rhombohedral distortion decreases with increasing x and the phase becomes cubic at x = 0.5. From the results of magnetic measurement, it was found that the cobaltite with x ≧ 0.05 is ferromagnetic. This result is explained by the itinerant-electron model.
Journal of Applied Electrochemistry | 1982
Y. Takeda; R. Kanno; T. Kondo; Osamu Yamamoto; H. Taguchi; M. Shimada; M. Koizumi
Strontium ferrates and cobaltates with compositions SrFeO3-δ (0.06⩽δ⩽0.40) and SrCoO3-δ (0.04⩽δ⩽0.30) were synthesized. The dependence of the oxygen electrode properties on the δ value was examined in 1 mol dm−3 KOH solution. In the SrFeO3-δ series, the samples with 0.24<δ<0.29, showed the highest activity in both oxygen evolution and reduction reactions. In contrast, no strong dependence on the δ value was observed in SrCoO3-δ, which also showed a high catalytic activity for oxygen evolution.
Journal of Solid State Chemistry | 1979
Y. Noda; M. Shimada; M. Koizumi; F. Kanamaru
Abstract The solid solution Fe(Nb 1− x W x )O 4 (0 ≦ x ≦ 1) with wolframite-type structure has been prepared under argon atmosphere at 1000°C. The change of unit cell parameters is not linear, owing to the zigzag chain of octahedra along the c -axis. The results of magnetic susceptibility and Mossbauer effect measurements indicate the existence of a mixed valence state of iron ions.
Journal of Solid State Chemistry | 1982
H. Taguchi; M. Shimada; M. Koizumi
Abstract The electrical resistivity of (La 1− x Ca x )CoO 3 (0.1 ≦ x ≦ 0.5) was measured in the temperature range from 80 to 300K. Cobaltite with x ≦ 0.15 is a semiconductor, but the specimen with chemical composition 0.2 ≦ x ≦ 0.5 is metallic. The change of temperature dependence of electrical resistivity has a break point around T c . The value of the logarithm of the specific electrical resistivity (log ϱ) at 300K has a minimum at x = 0.4, and this result is explained by the Zener double-exchange mechanism.
Journal of Solid State Chemistry | 1983
Fumikazu Kanamaru; S. Miyazaki; M. Shimada; M. Koizumi; Kiichi Oda; Y. Mimura
Abstract Amorphous Fe 100− x B x alloys were prepared by the rf-sputtering method in a chemical composition range of 18 ≤ x ≤ 42. The crystallization temperature of the amorphous alloys increases with the B contents up to near x = 36, above which the crystallization temperature decreases monotonically. This anomaly is reflected in the composition dependence of the Curie temperature and of the coercive force of the amorphous alloys.