No abstract

No abstract

No abstract

In the present work, we have obtained high magnitudes of the Seebeck coefficient in Sb and In coalloyed bismuth telluride thin film that has been deposited by a simple and cost-efficient thermal evaporation procedure. The films display an exceptional peak Seebeck coefficient of −310 μV/K at the working temperature of 90 °C. In addition to this, a high value of −191.6 μV/K is obtained at room temperature along with appreciable conductivity (6.2 × 103 S/m). The x-ray diffraction (XRD) pattern of the film has been analyzed for probing the crystal profile that depicts a polycrystalline and nanoscale structure. Films’ surface and cross-sectional morphologies are investigated using Field Emission Scanning Electron Microscope (FESEM), where a nanocrystalline morphology of thickness 150 nm is observed. Raman analysis supports the results obtained from XRD and FESEM for nanomorphology and indicates the presence of Te segregates. Atomic composition of the film produced is probed using Energy Dispersive x-ray spectroscopy, which also indicates the presence of excess Te. The Seebeck coefficient of the films shows an enormous enhancement as compared to previously reported work for undoped samples (BST-100S). The magnitudes of the Seebeck coefficient obtained in the present work are among the highest values reported for a bismuth antimony telluride material. These enhancements are attributed to the combined effect of coalloying, the presence of highly mobile (00l) orientations, and confinement effects of a nanocrystalline profile.

Bi/Ag2Se bi-layer (ASB) has been deposited using simple thermal evaporation. Both the layers are interdiffused thermally at transition temperatures of 130 (ASB-130) and at 210 °C (ASB-210) for a soaking time of 1 h each. ASB-210 shows a promising in-plane thermoelectric power factor of 1.4 mW/m K2 at 30 °C and 1.5 mW/m K2 at 90 °C. This ultrahigh value in ASB-210 is due to simultaneous improvement in carrier concentration and mobility values (enhances σ). Moreover, (013) grain orientation and uniform distribution of Ag and Bi in Ag2Se matrix are inferred to be other reasons for power factor improvement. The power factor of ASB-210 is found to be nearly stable in the temperature range of 30–90 °C. This constant value is accredited to suppression of bipolar effect in Ag2Se by Ag and Bi nano-inclusions. Ag, Bi impurities are held responsible for carrier scattering. Moreover, formation of Ag/Ag2Se and Bi/Ag2Se heterostructures promotes hot carrier filtering, which enhances the Seebeck coefficient. Thus, decoupling of electrical conductivity and Seebeck coefficient is achieved. This technique of enhancing thermoelectric performance has not been reported for Ag2Se films.