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

摘要

We find that Ag-interstitial ($Ag_I$) acts as an electron donor and plays animportant role in Ag-excess doped polycrystalline PbTe thermoelectricmaterials. When Ag is heavily doped in PbTe, the neutral (Ag-Ag) dimer defectis formed at the Pb-site and the environment becomes Pb-rich/Te-poor condition.Then the positively ionized Ag interstitial ($Ag_I^+$) defect becomes the majordefect under Pb-rich condition. Due to the small formation energy and smalldiffusion barrier of $Ag_I^+$, Ag can be easily dissolved into the PbTe matrix.The temperature behavior of the Ag defect formation energy well explains the$Ag_I^+$ solubility, the electron carrier generation, and the increasingelectrical conductivity in Ag-excess doped polycrystalline PbTe at hightemperature. This abnormal doping behavior by forming interstitial defects isalso found for Au-doped PbTe.