diffusion in the interstitial positions. As Cu exhibited donor properties in Bi2Te3-based alloys, the thermoelectric properties of these alloys changed with aging time because of the decrease in Cu atoms or Cu+ ions which were oxidized on the surface of the sample. By using the change in electrical conductivity with aging time, the mechanism of diffusion of Cu in polycrystalline Bi2Te3-based alloys fabricated by plastic deformation of hot pressing sample was investigated. Consequently, an activation energy of 9.44kJ/mol was obtained for Cu in the sample. Moreover, the rate of change in electrical conductivity decreased with the aging time and was inversely proportional to the aging time. This was expected to be due mainly to the deposition of Cu-oxide on the surface of the sample, which suppressed further oxidation of Cu atoms or Cu+ ions. Two models for oxidation of Cu on the surface of the Bi2Te3-based sample were considered and the rate of change in electrical conductivity as a function of aging time was explained.

Analysis of Diffusion Mechanism of Cu in Polycrystalline Bi2Te3-Based Alloy with the Aging of Electrical Conductivity. S.Fujimoto, S.Sano, T.Kajitani: Japanese Journal of Applied Physics, 2007, 46[8A], 5033-9