We present a detailed study of the charge transport, optical reflectivity, and thermal transport properties of n-type PbSe crystals. A strong scattering, mobility-limiting mechanism was revealed to be at play at temperatures above 500 K. The mechanism is indicative of complex electron-phonon interactions that cannot be explained by conventional acoustical phonon scattering alone. We applied the first order non-parabolicity approximation to extract the density of states effective mass as a function of doping both at room temperature and at 700 K. The results are compared to those of a parabolic band model and in the light of doping dependent studies of the infrared optical reflectivity. The thermal conductivity behavior as a function of temperature shows strong deviation from the expected Debye-Peierls high temperature behavior (umklapp dominated) indicating an additional heat carrying channel, which we associate with optical phonon excitations. The correlation of the thermal conductivity observations to the high temperature carrier mobility behavior is discussed. The thermoelectric figure of merit exhibits a promising value of ∼ 0.8 at 700K at ∼ 1.5 × 10 19 cm −3 .
Nano-crystalline lead telluride powder was synthesized by mechanical alloying using a high-energy planetary ball mill. The broadening of the X-ray diffraction peaks vs ball milling time, indicates small crystalline size of the order of 30nm. IR spectroscopy results are discussed and compared to the material prepared from melt.
In this work we report on the infrared properties of the thermoelectric (1-x)PbTe-xPbSnS2 system with x=0.03, 0.06, 0.11 and 0.33. The results obtained by the analysis of the reflectivity spectra are discussed together with the structural and morphological characteristics obtained by XRD and SEM-EDS measurements. The system was found macroscopically homogeneous for x=0.03 and x=0.06 and phase separated for x=0.11 and x=0.33. The analyzed ~150cm-1 PbS impurity mode demonstrated a composition close to the PbTe0.98S0.02 for the major phase. The incorporation of PbSnS2 causes a reduction in plasma frequency (decrease in carrier frequency concentration) and an increase in carrier mobility.
In this work, room temperature co-deposition of Mg and Si was used to successfully fabricate Mg 2 Si thin films on Si substrate by dual cathode magnetron sputtering (DCMS). Films were annealed at 380°C. Various Mg/Si sputtering power ratios have been examined. XRD, SEM and IR reflectivity measurements on grown and annealed films, reveal that annealing is enhancing the formation of crystalline Mg 2 Si.
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