Antimony (Sb)-doped PbTe nanostructured alloys with improved optical and thermoelectrical characterizations for clean energy applications

The current work investigates the influence of antimony doping on the morphology, optical behavior, and thermoelectric performance of PbTe nanostructures fabricated using the hydrothermal method. Analyses employing X-ray diffraction (XRD) and Raman spectroscopy techniques asserted the existence of the cubic phase, a defining characteristic of PbTe compounds. The morphology and internal structure of the samples are examined by the scanning and high-resolution transmission electron microscopes. The photoluminescence spectra show a band gap energy around 3.0 eV which is higher than that of the bulk sample. Raman spectra show three peaks corresponding to longitudinal optical (LO) phonon mode and higher-harmonic multiphonon process of PbTe. The PL spectra exhibit a strong peak at the wavelength 401 nm which is ascribed to a recombination of excitons and/or shallowly trapped electron–hole pairs. The thermoelectric properties are studied in the temperature range of 300–500 K and confirm the domination of p-type conduction in the whole temperature range. The electrical conductivity (σ) versus temperature showed thermally activated behavior as the charge carrier mobility is activated and the average carrier kinetic energy increases with temperature. Activation energy was obtained from the plots of Ln σ as a function of 1000/T. The recorded values were found at 62, 50,73 and 34 meV for x = 0, 0.04, 0.06 and 0.08, respectively. The Seebeck coefficients (S) of the synthesized nanostructures revealed a dominance of p-type conduction due to consistently positive S values. The S-T plots exhibit an initial increase in S with temperature at lower values (T < Tₛ). However, a transition occurs at a specific temperature (Tₛ), marked by a step change in S from positive to negative values, followed by a decrease in S with further temperature rise (T > Tₛ). The highest Seebeck coefficient was observed around 196.2 μV/K and recorded at 418 K for the sample of x = 0.04 Sb content. The largest power factor was recorded at 13.6 × 10⁻⁵ W. m⁻¹. K⁻², obtained for pure PbTe at 438 K due to the high value of electrical conductivity.