In the frame of the current research, the -type Bi2Te3 doped (GeTe)0.95(Bi2Te3)0.05 alloy composed of hot pressed consolidated submicron structured powder was investigated. The influence of the process parameters (i.e., powder particles size and hot pressing conditions) on both reduction of the lattice thermal conductivity and electronic optimization is described in detail. Very high maximal ZT values of up to ～1.6 were obtained and correlated to the microstructural characteristics. Based on the various involved mechanisms, a potential route for further enhancement of the ZT values of the investigated composition is proposed. 1. Introduction Thermoelectrics as a direct energy conversion method between heat and electricity is mainly used for electrical power generation and cooling applications. Germanium telluride based alloys are known as appropriate candidates for -type legs in thermoelectric applications for the 50–500°C temperature range, exhibiting high dimensionless thermoelectric figure of merit , where is the Seebeck coefficient, is the electrical resistivity, is thermal conductivity, and is absolute temperature) values. GeTe based compounds are characterized by a continuous phase transition from a low temperature rhombohedral to a high temperature cubic rock salt structure that takes place at 427°C in pure GeTe [1]. Germanium telluride based alloys are characterized by a large deviation from stoichiometry toward tellurium rich compositions. The main nonstoichiometric defects are doubly ionized metal vacancies. As a result of this deviation from stoichiometry, GeTe always exhibits -type conductivity ( ~1020–1021？cm？3) [2]. To reduce the hole concentration, in order to obtain optimal thermoelectric properties, it is necessary to dope GeTe with donor type electroactive impurities. Bi2Te3 [3] and PbTe [4] act as donors while dissolved in GeTe. A mechanism of doping GeTe by Bi2Te3 has been put forward by Gelbstein et al. [2], according to which the latter is implanted into the GeTe lattice in the form of complexes consisting of a single electroneutral cation vacancy per each Bi2Te3 molecule implanted. The introduction of Bi2Te3 into the GeTe lattice changes the cation-anion ratio and the vacancy formation is due to the requirement for charge equilibrium. The reduction of the hole concentration in GeTe after introducing Bi2Te3 is associated with the filling of the cation vacancies by germanium atoms present in GeTe as a second phase. High thermoelectric performance was recently reported by PbTe alloying of GeTe for obtaining quasi-binary alloys that
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