Enhancement of electrical performance via carrier modulation in single crystalline PbTe prepared by Pb-flux method

Single crystalline PbTe samples are prepared by the Pb-flux method according to the stoichiometric ratio of Pb1+xTe (x = 1.5, 2.0, 2.5, and 3.0). Experimental results show that all the samples exhibit n-type conductivity. The order of magnitude for carrier concentration is 1019, which is one order of magnitude higher than that in pure n-type PbTe sample (2.56 x 1018 cm(-3)). The highest power factor reaches 2.07 x 10(-3) W m(-1) K-2 at 420 K for the sample with x = 1.5, which is an approximately 30% enhancement compared with the polycrystalline sample (1.59 x 10(-3) W m(-1) K-2). In a theoretical study on the PbTe system, Te vacancy (V-Te) is preferentially formed under the Pb-rich condition. To further understand the effect of V-Te on the electrical performance of PbTe thermoelectric material, the electronic structures of PbTe with V-Te are determined by first principle calculations. Theoretical calculations reveal that V-Te can modify the electronic density of states by introducing resonant level, which can increase the number of carrier pockets. Consequently, carrier concentration has increased remarkably. In this study, a Pb-flux method for synthetizing single crystalline PbTe thermoelectric material is convenient and low cost, and it has potential for mass production in commercial applications. (C) 2018 Elsevier B.V. All rights reserved.