연구홍보포털

논문 초록 (Abstract)

Density functional calculations have been performed to investigate the role of Ag defects in PbTe thermoelectric materials. Ag-defects can be either donor, acceptor, or isovalent neutral defect. When Ag is heavil y doped in PbTe, the neutral (Ag-Ag) dimer defect at Pb-site is formed and the environment changes to the Pb-rich/Te-poor condition. Under Pb-rich condition, the ionized Ag-interstitial defect (Ag-I(+)) bec omes the major donor. The formation energy of Ag-I(+) is smaller than ot her native and Ag-related defects. Also it is found that Ag-I(+) is an effective dopant. There is no additional impurity state near the b and gap and the conduction band minimum. The charge state of Ag-I(+) d efect is maintained even when the Fermi level is located above the condu ction band minimum. The diffusion constant of Ag-I(+) is calculated base d on the temperature dependent Fermi level, formation energy, and migra tion energy. When T > 550 K, the diffusion length of Ag within a few mi nutes is comparable to the grain size of the polycrystalline PbTe, imply ing that Ag is dissolved into PbTe and this donor defect is distribute d over the whole lattice in Ag-excess doped polycrystalline PbTe. Th e predicted solubility of Ag-I(+) well explains the increased electr on carrier concentration and electrical conductivity reported in Ag-e xcess doped polycrystalline PbTe at T = 450-750K [Pei et al., Adv. Energ y Mater. 1, 291 (2011)]. In addition, we suggest that this abnormal doping behavior is also foundfor Au-doped PbTe. (C) 2015 AIP Publishing LLC.