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論文

Influence of sedimentation of atoms on structural and thermoelectric properties of Bi-Sb alloys

Januszko, K.*; Stabrawa, A.*; 緒方 裕大; 徳田 誠*; Khandaker, J. I.*; Wojciechowski, K.*; 真下 茂*

Journal of Electronic Materials, 45(3), p.1947 - 1955, 2016/03

 被引用回数:2 パーセンタイル:18.51(Engineering, Electrical & Electronic)

Functionally graded thermoelectric materials (FGTMs) have been prepared by sedimentation of atoms under a strong gravitational field. Starting samples of Bi$$_x$$Sb$$_{1-x}$$ alloys with different composition x were synthesized by melting of metals and subsequent annealing of quenched samples. Strong gravity experiments were performed in a unique ultracentrifuge apparatus under acceleration of over 0.5$$times$$10$$^6$$ G at temperatures of 538 K and 623 K. As a result of sedimentation, large changes in chemical composition (x = 0.45 to 1) were obtained. It was found that the changes in chemical composition were correlated with alterations of the Seebeck coefficient. The obtained experimental data allowed the development of a semiempirical model for the selection of optimal processing parameters for preparation of Bi-Sb alloys with required thermoelectric properties.

論文

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

緒方 裕大*; 井口 裕介*; 徳田 誠*; Januszko, K.*; Khandaker, J. I.*; 小野 正雄; 真下 茂*

Journal of Applied Physics, 117(12), p.125902_1 - 125902_6, 2015/03

 被引用回数:6 パーセンタイル:32.7(Physics, Applied)

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.

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