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Title: Defects responsible for abnormal n-type conductivity in Ag-excess doped PbTe thermoelectrics

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 heavily 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{sub I}{sup +}) becomes the major donor. The formation energy of Ag{sub I}{sup +} is smaller than other native and Ag-related defects. Also it is found that Ag{sub I}{sup +} is an effective dopant. There is no additional impurity state near the band gap and the conduction band minimum. The charge state of Ag{sub I}{sup +} defect is maintained even when the Fermi level is located above the conduction band minimum. The diffusion constant of Ag{sub I}{sup +} is calculated based on the temperature dependent Fermi level, formation energy, and migration energy. When T > 550 K, the diffusion length of Ag within a few minutes is comparable to the grain size of the polycrystalline PbTe, implying that Ag is dissolved into PbTe and this donor defect is distributed over the whole lattice in Ag-excess doped polycrystalline PbTe. The predicted solubility of Ag{sub I}{sup +}more » well explains the increased electron carrier concentration and electrical conductivity reported in Ag-excess doped polycrystalline PbTe at T = 450–750 K [Pei et al., Adv. Energy Mater. 1, 291 (2011)]. In addition, we suggest that this abnormal doping behavior is also found for Au-doped PbTe.« less
Authors:
; ; ; ; ; ; ;  [1] ;  [2]
  1. Thermoelectric Conversion Research Center, Korea Electrotechnology Research Institute (KERI), 642-120 Changwon (Korea, Republic of)
  2. Department of Advanced Materials Engineering, Hanbat National University, 305-719 Daejeon (Korea, Republic of)
Publication Date:
OSTI Identifier:
22490767
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Applied Physics; Journal Volume: 118; Journal Issue: 1; Other Information: (c) 2015 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; CHARGE STATES; DENSITY FUNCTIONAL METHOD; DIFFUSION LENGTH; DOPED MATERIALS; ELECTRIC CONDUCTIVITY; FERMI LEVEL; FORMATION HEAT; GRAIN SIZE; LEAD TELLURIDES; POLYCRYSTALS; THERMOELECTRIC MATERIALS