2021 年 62 巻 2 号 p. 149-154
Thermoelectric properties of quasicrystalline approximants have been reasonably described by the semiclassical Boltzmann transport theory under the empirical constant-diffusivity approximation. To investigate why the approximation could provide such a reasonable description, the properties of an Al–Cu–Ir cubic approximant at temperatures between approximately 400 K and 1000 K were reinvestigated on the basis of a quantum-mechanical transport theory that takes into account two effects missing in the Boltzmann theory, i.e., the interband contribution and the lifetime broadening. The present theory describes the properties as the constant-diffusivity approximation. However, 45(5)% to 66(4)% of electrical conductivity is accounted for by the interband contribution. Spectral diffusivity is less energy-dependent within the electron lifetime necessary for describing the measured properties of the approximant [2.2(3) fs to 3.8(6) fs], which is why the constant-diffusivity approximation could reasonably describe the properties even though the interband contribution is not explicitly taken into account.
