Characterization of the Structural Modulations in n-type Bi₂ (Te₀.95Se₀.05)₃ Thermoelectric Compound

An n-type Bi₂Te₃ thermoelectric compound was analyzed by using a high resolution transmission electron microscopy, and was further analyzed by using an image processing unit. A sinusoidal strain contrast of the structural modulations appeared in a multi-beam image and the fringes showed a wavelength of 12 nm with a wave vector parallel to the {101‾ 10} planes. A numerous dislocations were found to glide on to the (0001) plane with a Burgers vector of 1/3<21‾1‾0>-type on the strain field. In order for the elastic strain energy to be relieved, the resultant 1/3<21‾ 1‾0>-type dislocation was thought to be dissociated into two partial dislocations gliding on the {1‾015} planes. The variation in stacking periodicity of the 5-layers lamellar structure with respect to the basal plane of Bi₂Te₃ was also observed locally. However, this stacking variation is not responsible for the formation of structural modulations. The displacement of the sinusoidal strain field on the structural modulations seems to be generated by dislocation, with presence of dipoles that are about a few nanometers apart. It is understandable that phonons should be scattered throughout the strain field of the structural modulation. Hence, the lattice thermal conductivity is expected to be decreased due to the phonon scattering on sinusoidal strain field of the structural modulations