Makoto Tokuda

Diffusion phenomenon at the interface of Cu-brass under a strong gravitational field

To investigate diffusion phenomenon at the interface between Cu and brass under a strong gravitational field generated by ultracentrifuge apparatus, we performed gravity experiments on samples prepared by electroplating with interfaces normal and parallel to the direction of gravity. For the parallel-mode sample, for which sedimentation cannot occur thorough the interface, the concentration change was significant within the lower gravity region; many pores were observed in this region. Many vacancies arising from crystal strain due to the strong gravitational field moved into the lower gravity region, and enhanced the atoms mobilities. For the two normal-mode samples, which have interface normal to the direction of gravity, the composition gradient of the brass-on-Cu sample was steeper than that for Cu-on-brass. This showed that the atoms of denser Cu diffuse in the direction of gravity, whereas Zn atoms diffuse in the opposite direction by sedimentation. The interdiffusion coefficients became higher in the Cu-on-brass sample, and became lower in the brass-on-Cu sample. This rise may be related to the behavior of the vacancies.

Formation of graded vanadium oxide (V–O compound) under strong gravitational field

Sedimentation of atoms induced under strong gravitational field gives a tool for controlling elemental compositions in condensed matter. We performed a strong-gravity experiment (0.397 × 106 G at 400 °C for 24 h) on a V2O5 polycrystal using the high-temperature ultracentrifuge to examine the composition change and further the structure change. The graded composition structure of V and O was formed along gravity direction, where V increases and O decreases with gravity. It was found by the x-ray diffraction and Raman scattering method that VO2 and V2O3 phases appeared and the amounts increased, while one of the V2O5 phase decreased gradually along gravity direction. The X-ray absorption near edge structure spectra analysis identified the chemical valency decrease (+5 to +3). The UV-Vis absorption spectroscopy addressed the shifting in center of major absorption peak to longer wavelength (red shift) with the increase in gravitational field. The tail absorption peak (band gap 2.09 eV) at strong gravity regio...

The vanadate garnet Ca2NaCd2V3O12: a single-crystal X-ray diffraction study

Single crystals of the vanadate garnet Ca2NaCd2V3O12 (dicalcium sodium dicadmium trivanadate) were synthesized using the floating-zone method and the crystal structure was investigated using single-crystal X-ray diffraction. We considered the effectiveness of substitution of the Y-site cation with reference to previous structural studies of vanadate garnets. The structures of vanadate garnets are subject to geometric constraints similar to those of silicate garnets. These constraints force the tetrahedral-dodecahedral shared edge length in vanadate garnets to become shorter than the unshared dodecahedral edge length, as in ugrandite (uvarovite, grossular and andradite) garnets. However, the vanadate garnet Ca2NaCd2V3O12 exhibits the normal structural feature, similar to pyralspite (pyrope, almandine and spessartine) garnets, namely that the dodecahedral-dodecahedral shared edge length is shorter than the unshared dodecahedral edge length. With increasing ionic radius of the Y-site cation, the atomic coordinates x, y and z of oxygen adopt values which satisfy Paulings third rule.

Change in crystal structure and physical properties of the Multiferroics YMnO3 single crystals by Strong gravitational field

Many researchers have studied the multiferroicity of the hexagonal RMnO3 (R: rare-earth element) for both applications and fundamental studies. To investigate the relationship between the structure and physical properties of materials, some people apply the chemical pressure effect. The procedure of chemical pressure effect involves substituting rare-earth elements for ones which have a different ionic radius. Mashimo et al. have developed a high-temperature ultracentrifuge apparatus that can generate extended duration strong gravitational field in excess of 106 G under a wide range of temperatures (up to 500°C). Strong gravitational fields directly act on each atom as a different body force. This can cause the change in crystal structure. Thus, we subjected YMnO3 single crystal to strong gravity experiments (0.78×106 G, 400°C, 2 h) and investigated the resulting changes in the crystal structure and physical properties of the gravity sample. The single crystal four-circle X-ray diffraction measurements revealed the change in the nearest neighboring Mn-Mn and M-O bond distances. The temperature dependence of magnetic susceptibility by SQUID showed the change in the magnetic anisotropy of gravity sample.

Effect of strong gravitational field on oriented crystalline perovskite-type manganese oxide La1−xSrxMnO3

We report the effect of a strong gravitational field on oriented crystalline perovskite-type manganese oxide La1−xSrxMnO3 (LSMO). The perovskite-type manganese oxides La1−xSrxMnO3 (LSMO) have been investigated for giant magnetoresistance (GMR) by controlling the hole-doping level (x). A strong gravitational field can change in crystalline state and the enhancement of usual diffusion. We subjected oriented crystalline La1−xSrxMnO3 with different grain and grain-boundary (GBs) Sr concentrations to a strong gravitational field and investigated the resulting changes in the A-site cation diffusion and physical properties of the material. Electron probe micro-analysis (EPMA) results showed appearance of the GBs where the Sr concentration was quite high compared with in other GBs. The quantitative analysis at the grain and GBs indicated that cation diffusion was more enhanced than the annealed one. The temperature dependence of the magnetic susceptibility of the gravity samples changed with the Sr concentration in the grains. The temperature dependence of the resistivity curves of the gravity sample showed several abrupt changes, which corresponded to phase transitions at the grains and GBs, which may be caused by composition changes.

Crystallization and reconstructive layer transformation of a-Si/Au multilayer thin films under a strong gravitational field

There were still unclear questions in the new method that fabricate the high quality poly crystalline Si thin film from amorphous Si thin film with lower annealing temperature than conventional Si recrystallization temperature. In that recrystallization process, the recrystallization mechanism was generally explained by the MIC (Metal Induced Crystallization) of Au. In this paper, we have discussed the effects of film structure and strong gravity on recrystallization, by using conventional furnace and high-temperature ultracentrifuge furnace system. The five kinds of samples (two bilayered Si/Au thin films, two multilayered Si/Au thin films and trilayered Si/Au/Si thin film) and found the effects of structure and strong gravity. The best for crystallization was Au/Si multilayered thin film, which is almost finished to crystallize even at 673 K annealing. The strong gravity advanced and retreated the crystallization, depending to thin film structure.

Formation of Vanadium Oxide (V-O System) Graded Compounds under Strong Gravitational Field

Strong gravitational field induces sedimentation of atoms due to the different body forces acting on respective atoms, and gives a tool for controlling elemental compositions in condensed matter. Vanadium oxide (V-O system) has large contrast in phases like VO, V2O3, VO2, V2O5 etc., and shows the respective interesting diverse electrical and optical properties. We performed a strong-gravity experiment (0.397106G at 400°C for 24 hours) on a V2O5 polycrystal using the high temperature ultracentrifuge to examine the composition change and further the structure change. It was found by the XRD and Raman scattering method that VO2 and V2O3 phases appeared and the amounts were increased, while one of the V2O5 phase decreased gradually along with the increasing gravitational field.

Strong-Gravity Experiments on Perovskite-Type Oxides

Strong gravitational field causes the displacement or/and sedimentation of atoms in solids, by which we can changes the crystalline state or/and composition in multicomponent condensed matter. Perovskite-type doped manganite, La1-xSrxMnO3 (LSMO) has unique magnetoresistance effect which is called “colossal magnetoresistance (CMR)”. In this study, the strong gravity experiment (0.40x106G, 400°C, 20h) was performed on the LSMO oriented crystal to examine the change in composition or structure. The LSMO crystal whose growing crystal direction is normal to (214) plane was prepared by the floating zone method. The EPMA and XRD results of the gravity sample revealed that the La compositions decrease in the crystal grain, while the structure did not change much. The SQUID analysis showed that the magnetic property of the gravity sample had changed.