The search for alternative energy sources is presently at the forefront of applied research. In this context, thermoelectricity for direct energy conversion from thermal to electrical energy plays an important role. This paper is concerned with the development of highly efficient p-type [(PbTe)(SnTe)(Bi 2 Te 3 )] x (GeTe) 1Àx alloys for thermoelectric applications using spark plasma sintering (SPS). Varying the carrier concentration of GeTe was achieved by alloying of PbTe, SnTe, and/or Bi 2 Te 3 . The rhombohedral to cubic phase transition temperature, T c , was found to be sensitive to the degree of alloying. Highest power factor values (P £ 33 lW/cm K 2 ) were obtained for (GeTe) 0.95 (Bi 2 Te 3 ) 0.05 composition.

The search for alternative energy sources is presently at the forefront of applied research. In this context, thermoelectricity for direct energy conversion from thermal to electrical energy plays an important role. This paper is concerned with the development of highly efficient p-type Ge x Pb 1Àx Te alloys for thermoelectric applications, using spark plasma sintering. The carrier concentration of GeTe was varied by alloying of PbTe and/or by Bi 2 Te 3 doping. Very high ZT values up to $1.8 at 500°C were obtained by doping Pb 0.13 Ge 0.87 Te with 3 mol% Bi 2 Te 3 .

This work is concerned with Bi2Te3-based compounds known as being highly effective materials for thermoelectric applications near room temperature. These compounds are characterized by a remarkable anisotropy linked to their R3¯m crystal structure. Two textured p-type Bi0.4Sb1.6Te3 samples were prepared using a powder metallurgy approach, with the c axis parallel to the pressing direction. One sample was undoped while the second was doped with Pb which acts as an acceptor. The electrical conductivity, Hall coefficient, and magnetoresistivity were measured from room temperature down to 6K. The Seebeck coefficient α and electrical conductivity σ were measured along and perpendicular to the c axis from 300 up to 550K, and the thermal conductivity κ was measured at 300K. Different values of Seebeck coefficient were observed along and perpendicular to the c axis at temperatures above Ti, the beginning of intrinsic region in which the influence of the minority carriers becomes significant. Below Ti, the Seebeck coefficient was isotropic. The maximal power factor P=α2σ, calculated on the basis of the experimental results, was about 40μWcm−1K−2 for the direction perpendicular to the c axis. The thermal conductivity values for the temperature domain above 300K were calculated on the basis of a physical model and the measured values at 300K. The calculated values of the figure of merit Z=P∕κ were 3×10−3 and 2×10−3K−1 at 300 and 400K for the two samples, respectively. These values are comparable to those observed in Bi2Te3-based single crystals, thus making the powder metallurgy approach appropriate for thermoelectric conversion applications.

converters was successfully initiated by the development of various highly efficient TE material classes. Such materials require a unique combination of electronic (i.e., Seebeck coeffi cient ( α ), electrical resistivity ( ρ ), electronic thermal conductivity ( κ e ), and lattice (i.e., lattice thermal conductivity ( κ l )) properties, enabling the highest possible TE fi gure of merit ( ZT = α 2 T /[ ρ ( κ e + κ l )], where T is the absolute temperature values, for achieving signifi cant heat-to-electricity conversion effi ciencies. AB (where A is Pb, Sn, and Ge, and B is Te, Se, and S) chalcogenides and their alloys are narrow band-gap semiconductors, known as the most effi cient TE alloys for intermediate working temperatures of up to 600 °C. Yet, due to the fact that the electronic properties (i.e., α , ρ , and κ e ) are strongly coupled and follow opposite trends (i.e., α and ρ are decreased, and κ e is increased) upon increasing the carrier concentration (for example, by introducing the doping elements), most of the recently published highly effi cient chalcogenides were mainly focused on applying the advanced nanostructuring approaches for κ l reduction, and correspondingly enhancement of ZT due to lattice modifi cations. Such approaches included alloying methods (e.g., with SrTe, [ 1,2 ] MgTe, [ 3 ] and CdTe, [ 4 ] generating embedded strained endotaxial nanostructures, for the case of PbTe), the usage of layered structures, effectively scattered phonons (e.g., SnSe, [ 5 ] and approaching phase separation reactions, generating thermodynamic-driven nanoscale modulations (e.g., Ge x Pb 1-x Te [6][7][8] and Ge x (Sn y Pb 1-y ) 1-x Te. [ 9,10 ] All of these approaches resulted in a signifi cant increase of ZT up to ≈2.5 [ 5 ] due to an effective scattering of phonons by the associated generated nanofeatures.Regarding electronic optimization, for maximizing the α 2 / ρκ e component of ZT , besides using standard doping elements (e.g., PbI 2 and Bi as donors, and Na as an acceptor) for a moderate tuning of the carrier concentrations toward TE optimal values in the range of 10 19 cm −3 , attempts for TE electronic optimization of chalcogenides were so far focused on increasing the carrier effective mass by the convergence of electronic bands (e.g., enhancing the effect of heavy holes on account of light holes in degenerate PbSe [ 11 ] and GeTe [ 12 ] alloys). Distortion of the electronic density of states by the generation of resonant states and pinning of Fermi energy at TE optimal energetic locations (e.g., Tl- [ 13 ] and In-doped

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