Protections of the aging of n-type Bi–Te thermoelectric materials doped with Cu or Cu-halide

In Bi2Te3-based alloys doped with Cu or Cu-halide, Cu atoms diffuses very fast in the interstitial positions. As Cu shows donor properties in Bi2Te3-based alloys, thermoelectric properties of these alloys changes with the aging time because of the decrease of Cu atoms or Cu+ ions which are oxidized on the surface of the sample. To prevent the changes of thermoelectric properties of the polycrystalline Bi2Te3-based samples doped with Cu or Cu-halide fabricated by plastic deformation, complex doping and depositing protects of oxidation for the prevention of the diffusion or the oxidation of Cu were done. Consequently, complex doping of Cu and Al, Ge, or Ga were tested, but the changes of thermoelectric properties still remained. On the other hand, from the result of an accelerated test, it was found that the change of Seebeck coefficient of the sample to which Al2O3 thin-film protects were deposited on the lateral sides by sputtering method was very small. Moreover, the change of Seebeck coefficient of the sample with Ni plating on the plane perpendicular to current direction was smaller than that of the sample without Ni plating. Thus, not only Al2O3 thin-films on the lateral side but also Ni plating on the plane perpendicular to current direction are effective as the protects of oxidation of Cu in Bi2Te3-based samples.