EFFECTS OF Pb DOPING ON THE SEEBECK CO-EFFICIENT AND ELECTRICAL PROPERTIES OF Tl8.67PbxSb1.33-xTe6 CHALCOGENIDE SYSTEM

We present the effects of Pb doping on the electrical and thermoelectric properties of Tellurium Telluride Tl8.67PbxSb1.33-xTe6 (x= 0.61, 0.63, 0.65, 0.67, 0.68, 0.70), prepared by solid state reactions in an evacuated sealed silica tubes. Additionally crystal structure data were used to model the data and support the findings. Structurally, all these compounds were found to be phase pure as confirmed by the x-rays diffractometery (XRD) and energy dispersive x-rays spectroscopy (EDS) analysis. The Seebeck co-efficient (thermopower) (S) was measured for all these compounds which show that S increases with increasing temperature from 295 to 550 K. The Seebeck coefficient is positive for the whole temperature range, showing p-type semiconductor characteristics. Complex behavior of Seebeck coefficient for Pb doped compounds has been observed that at room temperature, the values of S for Pb based compounds have complex behavior, first S decreasing with increase in Pb concentration i.e. x=0.65, and then S increases with increase in Pb contents upto x=0.70. Similarly the electrical conductivity (sigma) and the power factors have also complex behavior with Pb concentrations. The power factor (PF=S-2 sigma) observed for Tl8.67PbxSb1.33-xTe6 compounds are increases with increase in the whole temperature range (290 K-550 K) studied here. Telluride's are narrow band-gap semiconductors, with all elements in common oxidation states, according to (Tl+) 9(Sb3+)(Te2-)(6). Phases range were investigated and determined with different concentration of Pb with consequents effects on electrical and thermal properties.