Masami Tsubota

Structural, transport, and thermal properties of the single-crystalline type-VIII clathrate Ba8Ga16Sn30

The analysis of temperature dependence of mH suggests a crossover of a dominant scattering mechanism from ionized impurity to acoustic phonon scattering with increasing temperature. The existence of local vibration modes of Ba atoms in cages composed of Ga and Sn atoms is evidenced by analysis of experimental data of structural refinement and specific heat, which give an Einstein temperature of 50 K and a Debye temperature of 200 K. This local vibration of Ba atoms should be responsible for the low thermal conductivity s1.1 W / m K at 150 Kd. The potential of type-VIII clathrate compounds for thermoelectric application is discussed.

Ti 3d orbital change across metal-insulator transition in Ti2O3 : Polarization-dependent soft X-ray absorption spectroscopy at Ti 2p edge

The Ti 3 d electronic structure of Ti 2 O 3 across metal–insulator transition (MIT) has been investigated by means of polarization-dependent soft X-ray absorption spectroscopy (XAS) at the Ti 2 p edge. The XAS spectra exhibit a remarkable linear dichroism (LD) between the polarization vectors of the incident light parallel and perpendicular to the Ti ion pair along the c -axis. LD intensity is significantly reduced at 520 K in the metallic phase in comparison with that at 300 K in the insulating phase, indicating a large change in a 1 g and e g π orbital occupations. The results are qualitatively consistent with a recent theory, where the MIT is due to the change of the 3 d electronic configuration in the Ti pair along the c -axis driven by a change in the t 2 g level splitting relative to the on-site exchange interaction.

Coupling between Orbital and Lattice Degrees of Freedom in Y1-xCaxTiO3 (0 < x ≤0.75): A Resonant X-ray Scattering Study

We have studied the orbitally ordered states in Y 1- x Ca x TiO 3 (0 < x ≤0.75) by resonant X-ray scattering (RXS) near the Ti K -edge ( E ∼5 keV) and by powder X-ray diffraction measurements. The ...

Sm-Sb Bond Length in Mixed-Valence System of SmOs4Sb12

The detailed crystal structure of a mixed-valent skutterudite SmOs 4 Sb 12 has been investigated by synchrotron radiation powder diffraction. Although the lattice parameter monotonically decreases with decreasing temperature, Sm–Sb bond length decreases rapidly below 150 K. The temperature dependence of the bond length coincides with that of the change in the valence of the Sm ion. These facts suggest that the hybridization between 4 f - and conduction electrons is enhanced at low temperatures. In addition, an isotropic thermal atomic displacement parameter of the Sm ion is much larger than those of the Os and Sb ions. This fact indicates the presence of an anharmonic vibration of Sm ions.

Hole-doping and Pressure Effects on the Metal–Insulator Transition in Single Crystals of Y1-xCaxTiO3 (0.37 ≤x ≤0.41)

The measurements of electrical resistivity, magnetic susceptibility, specific heat, thermopower and powder x-ray diffraction under pressure have been performed on single crystals of Y 1- x Ca x TiO...

Improved room-temperature-selectivity between Nd and Fe in Nd recovery from Nd-Fe-B magnet

The sustainable society requires the recycling of rare metals. Rare earth Nd is one of rare metals, accompanying huge consumption especially in Nd-Fe-B magnets. Although the wet process using acid is in practical use in the in-plant recycle of sludge, higher selectivity between Nd and Fe at room temperature is desired. We have proposed a pretreatment of corrosion before the dissolution into HCl and the oxalic acid precipitation. The corrosion produces γ-FeOOH and a Nd hydroxide, which have high selectivity for HCl solution at room temperature. Nd can be recovered as Mn2O3-type Nd2O3. The estimated recovery-ratio of Nd reaches to 97%.

Resonant X-ray Scattering Study at Y K-edge in Y1-xCaxTiO3

Resonant X-ray scattering (RXS) in Y 1- x Ca x TiO 3 has been investigated near the Y K -edge. The resonant signal has been clearly found at a forbidden reflection, (500), and the intensity shows an azimuthal angle dependence with a twofold symmetry. The RXS intensities have almost no Ca concentration dependence, although the RXS intensities at the Ti K -edge markedly decrease with increasing Ca concentration. The origin of the RXS at the Y K -edge is clarified to be the deviation from 180° of the Ti–O–Ti bond angle, namely, the tilts of the octahedra around the Y ion. We also discuss the RXS mechanism at the main edge of the Ti K -edge.

Temperature-Dependent High-Resolution Photoemission Study of Y1-xCaxTiO3

Temperature-dependent high-resolution photoemission spectroscopy has been performed on Y1-xCaxTiO3 (x=0.37, 0.39, 0.41) single crystals. Electrons in Ti 3d bands are strongly correlated and clear metal-insulator transition is observed in the photoemission spectra for x=0.39. The spectral shapes of O 2p and Ti 2p states are temperature dependent indicating strong coupling between electronic states and lattice distortion.

Elastic properties of ferromagnetic Mott insulator YTiO3

Abstract YTiO3 has attracted interests because of a Mott insulator with a ferromagnetic transition at T c ≃29 K . We have measured temperature dependence of elastic moduli for a high-quality single-crystal of YTiO3 around Tc using an ultrasonic technique. It is plausible that the elastic anomaly at Tc arises from a usual magnetostriction effect.

A necessary criterion for obtaining accurate lattice parameters by Rietveld method

To obtain the lattice parameters accurately by the Rietveld method, the relationship between the lattice parameters and the peak-shift, which is the deviation in diffraction angle from the theoretical Bragg position, was studied. We show that the fitting accuracy of lattice parameters is related directly to the well reproducibility of the peak-shift. This study unveils that the peak-shift consists of the experimental and the analytical ones. The analytical peak-shift erroneously lowers a reliability factor Rwp, which has, so far, been the conventional criterion of fit. The conventional Rietveld method obtains a unit-cell which is a homothetic (proportional) unit-cell of the true one. We propose an additional criterion based on the peak-shift to obtain the true lattice parameters accurately. Our criterion can achieve reproducibility reasonably well for the experimental peak-shift, leading to highly improved accuracy of the lattice parameters.