M. Shimada

Preparation and characterization of stoichiometric CaFeO3

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.

The effect of oxygen vacancy on the magnetic properties in the system SrCoO3−δ (0 < δ < 0.5)

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.

Magnetic properties in the system La1−xSrxCoO3 (0.5 ≦ x ≦ 1.0)

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.

The electrical properties of ferromagnetic SrCoO3−δ (0 <δ <0.5)

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.

Magnetic properties in the system BaCo1−xMnxO3 and SrCo1−xMnxO3 (0 ≦ x ≦ 1)

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.

Magnetic properties in the system (La1−xCax)CoO3 (0≦ x ≦ 0.6)

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.

Properties ofSrMO 3-?(M=Fe, Co) as oxygen electrodes in alkaline solution

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.

Magnetic and electrical properties and Mössbauer effect in the solid solution Fe(Nb1−xWx)O4 (0 ⩽ x ⩽ 1)

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.

Electrical properties in the system (La1−xCax)CoO3 (0.1 ≦ x ≦ 0.5)

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.

Preparation, crystallization, and magnetic properties of amorphous Fe100−xBx (18 ≦ x ≦ 42)

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.