Keywords:Chalcogenides, Thermoelectrics, Flexible thermoelectric
In the present work, we performed the first-principles calculations with GGA in the form of PBE for the exchange-correlation energy functional, as implemented in the VASP code. Firstly, with different transition metals substitutions at Ag site, we observed the formation of impurity peak in density of states, either of the valance (VB) or conduction band (CB) edge depends upon the elements used. The small impurity peak near VB and CB edge is very effective in modifying the thermoelectric properties of Ag2S and to get the better TE property of p-type and n-type materials, respectively. Secondly, in order to confirm the theoretical results, we synthesized the selected compositions of Ag2-xTMxS, and investigated thermoelectric properties of in the 300-450 K temperature range where only the low temperature phase is obtained. Polycrystalline samples were prepared by using standard melting method.
For all the samples with substitutions of different atomic percentage in between 0.0 to 2.0 we observed n-type behavior in case of V, whereas with some other elements substitutions we observed p-type behavior. The electrical resistivity and Seebeck coefficient were monotonically decreased with increasing the amount of substituted elements while thermal conductivity remains low. Interestingly, both p and n-type of materials with non-toxic composition showed ductile nature which is very useful feature to make the flexible TE device.