In our previous study TiB2-reinforced sintered steel with the remarkably high Young’s modulus was obtained for enabling a leaner design of automobile parts. This high Young’s modulus seemed to be due to both the suitable reinforcing particles for steels and the high sintered density provided by hot-work process of sintered billet.
In this study increasing the sintered density was investigated by the process of single-pressing and single-sintering in which near net shape parts were simply and easily manufactured.
In the compacts of steel powders containing TiB2 particles, the liquid phase of Fe-B system formed above 1448 K and enhanced densification of the compacts. In case of 2-15 vol% TiB2 addition, since the effect of this liquid phase on the densification was appreciable, the sintered density above 98% of pore free density was achieved by the vacuum sintering at 1523 K. This high relative density realized the high Young’s modulus comparable to calculated value in each TiB2 contents.
The purpose of this study is to examine the influence of soil microbes on the degradation of pipe-shaped red iron oxide pigments. Since there are differences between the conditions of samples for observation and those for analysis in this study, two kinds of culture examinations were performed for the observation and identification of particles. In the culture examination for observation of particles, the pipe-shaped red iron oxide material was annealed to form pipe-shaped particles, which were used as culture samples. The culture samples and iron-reducing bacteria were placed in a liquid medium and cultivated. After cultivation, the particle shape and hue of the samples were observed using a digital microscope and a scanning electron microscope. In the culture examination for crystal identification, annealed and crushed pipe-shaped red iron oxide material was used. The particle samples and iron-reducing bacteria were placed in a liquid medium and cultivated. After cultivation, the samples were subjected to X-ray analysis for crystal identification. This study allowed obtaining information about the changes in shape of pipe-shaped red iron oxides under the influence of iron-reducing bacteria.
The S = 1/2 Heisenberg antiferromagnet on the Lieb lattice accompanied by frustrating interactions is studied by the numerical-diagonalization method. Numerical results suggest that the model of the lattice obtained by combination of the Lieb lattice and the square lattice shows nontrivial states with nonzero spontaneous magnetization smaller than one third of the saturation magnetization when the strength of the frustrating interaction is in a specific region. In the region, the spontaneous magnetization gradually changes by varying the strength of the frustration. We find that the quantum effect in frustrating interactions is related to the appearance of the phase in which such weak spontaneous magnetizations occur.
Synthesis and physical properties of the Pb-Ru based pyrochlores Pb2−xMxRu2O7−δ (M = Eu and Ca) have been studied. For Pb-Eu solid solution Pb2−xEuxRu2O7−δ, single phases were successfully synthesized by the solid-state reaction. Magnetic susceptibility measurements indicated the magnetic transition due to spin-glass freezing in the samples with x ≥ 0.8. From electric resistivity measurements, a crossover from metallic to semiconducting behaviors was observed in the range of 0.6 ≤ x ≤ 0.8. In the metallic region, normalized electric resistivity was found to be almost proportional to T2, indicating the strongly-correlated electron behaviors. The crossover between insulating and metallic phases can be caused by the strong electron-electron couplings between the itinerant 4d electrons. For Pb-Ca solid solution Pb2−xCaxRu2O7−δ, single phases were obtained for x ≤ 0.6 samples by heat treatments in air. Pb2−xCaxRu2O7−δ samples with 0.8 ≤ x ≤ 1.6 were successfully synthesized under high oxygen pressures. Lattice parameter of Pb2−xCaxRu2O7−δ compounds was found to decrease with Ca content x, resulting in the positive chemical pressure. As a result of electric resistivity measurements, the samples with 0.0 ≤ x ≤ 1.0 showed the metallic behaviors.
Metal-oxygen bonds are responsible for a broad spectrum of functional properties of transition-metal oxides, and engineering the bonds is a key for exploring their properties. Artificial oxide heterostructures with chemically abrupt interfaces have provided a platform for engineering bonding geometries that could lead to emergent phenomena not seen in bulk oxides. In this paper, we demonstrate that interfacially engineering oxygen displacement is a good route for exploring structural and functional properties of oxides. Our high-resolution annular bright-field scanning transmission electron microscopy observations revealed that interfacial oxygen displacement determines metal-oxygen bond angles in entire heterostructures and the magnitude of the displacements can be adjusted by controlling propagations of the oxygen octahedral rotations across the heterointerface. We also show that by heterostructuring an itinerant ferromagnet SrRuO3 with Ca0.5Sr0.5TiO3 (0–4 monolayers thick) grown on a GdScO3 substrate, structural phase and magnetic anisotropy of SrRuO3 can be controlled through the interfacial engineering of its oxygen displacement.
To understand magnetism and electronic structures of compounds with CoAs layers, we compared results of experiments and band calculations of LiCoAs, LaCoAsO, and Sr2ScO3CoAs, which are all in the tetragonal crystal structure with the space group of P4/nmm. As a result of synthesis and magnetic measurement, we newly found that LiCoAs shows the Pauli paramagnetism with a small exchange-enhancement. Results of band calculations of three compounds are consistent with the experimental ones. Band structures show that magnetism of compounds with CoAs layers is strongly influenced by the distance between Co atoms within CoAs layer and thickness of it, while the interlayer distance of CoAs layers and the components of in-between layers less influence on their magnetism.
The influence of strain in the Nd-Fe-B was investigated by using the structural phase transition of BaTiO3 in films consisting of a Mo top layer (10 nm), Nd-Fe-B (30 nm), and a Mo bottom layer (20 nm) deposited onto BaTiO3 (001) substrates by sputtering. As a result, it was found that the magnetization along the easy axis jumps up in magnitude by 3% at around 280 K. This significant effect is certainly due to the lattice strain accompanying the structural phase transition of BaTiO3 from orthorhombic to tetragonal. First-principles calculations were applied to simulate the relationship between magnetization, magnetocrystalline anisotropy and the strain in the Nd-Fe-B main phase. It was also found that the magnetization along the easy axis increases as the lattice constant of the a-axis expands, which shows mostly good agreement with the experimental results under some assumptions.
Sr0.5−xCaxBi0.5FeO3 (0.0 ≤ x ≤ 0.5) perovskite compounds, which are solid solutions between Sr0.5Bi0.5FeO3 (x = 0.0) that shows a single charge disproportionation (CD) transition and Ca0.5Bi0.5FeO3 (x = 0.5) that shows successive CD and intermetallic-charge-transfer (CT) transitions, were obtained by high pressure syntheses. The crystal structure at room temperature changes from rhombohedral (0.0 ≤ x ≤ 0.1) to orthorhombic (0.2 ≤ x ≤ 0.5). Unusual-high-valence Fe3.5+ ion is stabilized in the entire range of the solid solution at room temperature, and undergoes a charge transition to relieve the electronic instability. Fe3.5+ in the range 0.0 ≤ x ≤ 0.4 shows a single 3:1 CD transition (Fe3.5+ → 3/4Fe3+ + 1/4Fe5+), and Bi3+ ion does not act as counter cations accepting charges as in Ca0.5Bi0.5FeO3. The difference in the crystal structure symmetry does not influence the 3:1 CD transition, and the transition temperature decreases monotonously with increasing x in the region 0.0 ≤ x ≤ 0.4.
To elucidate magnetism and electronic states of X2Co12P7 with X = Ti, Zr and Hf, which are expected to be in a tetravalent state or a trivalent state with one d-electron, we measured magnetizations of polycrystalline samples of X2Co12P7 and compared their magnetic behaviors with that of itinerant ferromagnets Ln2Co12P7 (Ln = lanthanoids), the Curie temperature TC of which is approximately 150 K. As results of magnetization measurements, we found these compounds to show itinerant ferromagnetism with TC = 67, 149 and 133 K for X = Ti, Zr and Hf, respectively. This behavior is in contrast to the case of Ln2Co12P7 in which TC is almost independent of Ln. The lower TC for the case of X = Ti compared with Ln2Co12P7 suggests that the valence of Ti in this compound is +4 rather than +3 and ferromagnetism derived from Co is weakened due to the electron doping from Ti. On the other hand, in the case of X = Zr and Hf compounds, both TC have similar values to that for Ln2Co12P7, indicating that X are almost in the trivalent state. From the result of magnetization measurements, it is clear that there is no localized magnetic moment in these compounds. Therefore, d-electrons in trivalent Zr or Hf show itinerant nature in X2Co12P7.
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(誤)平成29年4月1日から平成30年3月31日まで
(正)平成30年4月1日から平成31年3月31日まで