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An atomic-scale graded structure has been formed previously in a Bi70Sb30 (at. %) alloy that is miscible in all proportions, by sedimentation of substitutional solute atoms under an ultrastrong gravitational field up to 1×106 G at 220–240 °C [T. Mashimo, T. Ikeda, and I. Minato, J. Appl. Phys. 90, 741 (2001)]. In this study, additional megagravity field experiments were performed on the Bi70Sb30 alloy and pure Bi at different temperatures below their melting points, to investigate the change in crystalline state under the ultrastrong gravitational field. For the Bi70Sb30 alloy ultracentrifuged at 191–205 °C, no change in composition was observed, and the grain sizes of the crystals decreased from several millimeters to tens of micrometers, while no distinct change in grain size was observed for the pure Bi ultracentrifuged under the same experimental conditions. The Bi70Sb30 alloy ultracentrifuged at 220–240 °C consisted of two regions with different morphologies–fine-grained crystals with grain sizes in ...

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.

Beginning with homogeneous samples of the superconducting phase Y1Ba2Cu3O7−x (Y123), we examined changes in structure and composition under a strong gravitational field and temperatures remarkably lower than the Y123 melting point. We observed essentially two-layers with different compositions caused by sedimentation of atoms. The layer exposed to the stronger gravitational field is composed of an Y123 phase that has a smaller unit cell volume compared with the initial sample, green, transparent, large single crystals of Y211, and a BaCuO2 phase. Despite the remarkably lower temperature, compositional and structural changes in addition to decomposition were found. The unit cell volume of the Y211 phase was larger than previously indicated by synchrotron x-ray diffraction (XRD) analysis. Refinement of the Y211 structure from the XRD data also showed that these crystals are very perfect due to a very high extinction coefficient 0.7(9)×10−6 and symmetrical arrangement compared with the superconducting phase ...

A large linearly graded structure on atomic scale up to 88 at. %/mm with oriented grown crystals was formed in selenium-tellurium (Se-Te) semiconductor using a strong gravitational field of one million G level at 260 °C. The lattice constants and the binding energies of Se and Te 3d electrons continuously changed along the direction of gravity accordingly, which indicated the formation of the graded band gap structure. The grown crystals showed the crystalline orientation with the c axis of hexagonal structure roughly perpendicular to the direction of gravity. It was found that the diffusion coefficient of sedimentation was larger than that of normal diffusion by more than 100 times, which suggested a different diffusion mechanism from the normal vacancy mechanism.