Fumikazu Kanamaru

Superconductivity in the infinite-layer compound Sr1-xLaxCuO2 prepared under high pressure

Abstract A new superconductor Sr 1- x La x CuO 2 ( x =0.1) was prepared applying high pressure synthesis. It has an infinite-layer structure and its T c equals 43 K. It is probably an electron-doped superconductor because the reductive atmosphere was critical for its preparation under high pressure.

Crystal structure analyses of the pyrochlore and fluorite-type Zr2Gd2O7 and anti-phase domain structure

Abstract The detailed structure investigations of Zr2Gd2O7 with pyrochlore- and fluorite-type structures have been carried out by X-ray single crystal method at room temperature. The bond distances between cations and oxide ions versus the site population for cations reasonably support that the fluorite phase is made up of the structure with microdomains of the pyrochlore. Sharp fundamental and diffuse superstructure reflections of the pyrochlore are interpreted assuming that anti-phase domain boundaries lie parallel to the &{211} and that domain sizes are not uniform. It should be proposed that the layers composed of the 48f site oxide ions are anti-phase boundaries. The probability density function maps and effective one-particle potentials of the pyrochlore structure reveal that the magnitudes of anharmonic thermal motions for the 48f site oxide ions are large toward the unoccupied 8b site. Compared to the s-pyrochlore phase (with sharp superstructure reflections), the 48f site oxide ions of the d-pyrochlore (with diffuse superstructure reflections) and fluorite phases have larger temperature factors and gentler potential curves. This is due to that the anti-phase domains are coherent each other and that their electron density distributions are the averages of individual domains.

Synthesis of a new perovskite CaFeO3

Abstract A new perovskite CaFeO 3 with a o = 3.770 A has been synthesized at high temperature and pressure. An isomer shift corresponding to the tetravalent state of iron and a Neel temperature of 120°K are obtained from Mossbauer spectra and magnetic susceptibility measurements.

Stability and antiphase domain structure of the pyrochlore solid solution in the ZrO2Gd2O3 system

The stability of the pyrochlore-type solid solution in the system (1−x)ZrO2xGdO1.5 has been studied by means of X-ray diffraction. The powder samples with the composition of 0.20≤x≤0.62 were synthesized by wet-chemical method. The X-ray diffraction study results in that the pyrochlore-type solid solution is stable within the compositional range of 0.33≤x≤0.60 at 1500°C, which is consistent with composition dependence of lattice constant and physical parameters in conductivity. Broad superstructure peaks of the pyrochlore-type have been observed in the X-ray powder diffraction for the samples within the compositional ranges 0.33≤x≤0.43 and 0.57≤x≤0.62 sintered at 1500°C, and 0.46≤x≤0.54 annealed at 1600°C. This is explained by forming domains with antiphase boundaries in the pyrochlore-type solid solution.

Structure of Sr4Fe6O13, a new perovskite-derivative in the SrFeO system

Abstract Crystal structure of Sr 4 Fe 6 O 13 was studied by means of a single-crystal X-ray diffraction method. The crystal structure is orthorhombic and belongs to one of perovskite-derivatives constructed from Fe 2 O 3 - and Sr 2 Fe 2 O 5 -slabs perpendicular to the b-axis. One third of ferric ions occupies a distorted octahedral site and others locates at two different lattice sites with five oxygen-coordination. In the SrFeO system, Sr 4 Fe 6 O 13 with a chemical composition of Sr 3 -slabs.

Mössbauer effect of FeOCl-pyridine complex

Abstract A Mossbauer effect study has been conducted on FeOCl-pyridine complex in the temperature range between 4.2° and 298°K. The isomer shift relative to Fe metal and the quadrupole splitting at 298°K are 0.36 ± 0.01 and 0.92 ± 0.01 mm/sec, respectively. An antiferromagnetic ordering occurs at 65 ± 3°K. The internal magnetic field is 435 ± 10 kOe at 4.2°K. The z axis of the electric field gradient tensor (|Vzz|> |Vxx| ⩾ |Vyy|, η being small) is shown to be parallel to the direction of the internal magnetic field and perpendicular to the crystalline b axis.

The preparation of NaCl-type Ti1−xAlxN solid solution

Ti1−xAlxN solid solutions (0 ≤ x < 0.6) with NaCl-type structures were synthesized by a rf-sputtering method. The lattice constant of the solid solutions linearly decreases with increasing Al content. For samples withx greater than 0.5, a remarkable lattice distortion was observed.

Exafs study of the fluorite and pyrochlore compounds in the system ZrO2-Gd2O3

Abstract The local structures of the fluorite and pyrochlore compounds in the system (1-x)ZrO2-xGdO1.5 (0.20≤×0.62) have been studied by means of EXAFS spectroscopy. The EXAFS results indicate that trivalent Gd ions are 8-coordinated in both the fluorite-type and the pyrochlore-type solid solutions in the compositional range 0.2≤×0.5, and that the mean coordination number of tetravalent Zr ions decreases from eight to six with increasing Gd content. This indicates that the oxygen vacancies are located adjacent to tetravalent Zr ions. Cluster models which are a part of the pyrochlore structure, are proposed in the region of the fluorite phase.

Structural, electrical and magnetic studies of infinite-layered Sr1−xLaxCuO2 superconductor

Abstract Superconductivities were investigated in infinite-layered Sr 1− x La x CuO 2 prepared in a reductive atmosphere under high pressure. Its solid solution limit was estimated to be just above x =0.10. The T c onset values were in a range of 42–44 K independently of x and all samples attained the zero resistivities. The volume fraction of the superconductor showed a maximum at x =0.10. Their oxygen contents were analyzed to be not more than 2. The value of thermoelectric power was negative but its Hall coefficient had a positive value in a temperature range from room temperature to 77 K for the x =0.10 sample. These results indicate that electrons were doped into the conduction plane in the infinite-layered compound.

EXAFS study of the fluorite-type compounds in the systems ( 1 − x ) ZrO2−xYbO1.5 ( x = 0.18 ≦ x ≦ 0.5 ) and Zr2Ln2O7 (Ln = Tb, Dy, Ho, Er, and Yb)

Abstract The local structures of the fluorite-type compounds with a composition of Zr 2 Ln 2 O 7 ( Ln = Gd, Dy, Ho, Er and Yb) have been studied by means of EXAFS spectroscopy. The EXAFS results indicate that Ln 3+ ions are essentially 8-coordinated by oxide ions but Zr 4+ ions are 6-coordinated. The distinct difference in coordination number between Zr 4+ and Ln 3+ ions means that the local structures of the fluorite-type Zr 2 Ln 2 O 7 are similar to the pyrochlore-type structure, even though both Zr 4+ and Ln 3+3 ions are located statistically at the cation sites (4a site) in the fluorite-type lattice. The local structure of the fluorite-type solid solution in the system ( 1 − x )ZrO 2 − x YbO 1.5 (0.18≦ x ≦0.50) has been also studied by EXAFS spectroscopy. The result indicates that the coordination numbers of Zr 4+ and Yb 3+ ions are 6 and 8, respectively, in the solid solution in the compositional range 0.18≦ x ≦0.50, and that the oxygen vacancies are located adjacent to Zr 4+ ions.