Native defects and impurity band behavior in half-Heusler thermoelectric NbFeSb
Yefan Tian1, Hangtian Zhu, Wuyang Ren
1Department of Physics and Astronomy, Texas A&M University, College Station, TX 77843, USA. jhross@tamu.edu.
Abstract:
To investigate the electronic behavior and magnetic properties of NbFeSb, we have performed 93Nb NMR, specific heat and magnetic measurements on NbFeSb samples heat treated at high temperatures. Magnetic measurements combined with an observed Schottky anomaly and changes in the NMR line width indicate the presence of a 0.2% concentrated native magnetic defect in stoichiometric NbFeSb samples. The origin of these native defects is believed to be due to Fe antisites on Nb sites. In addition, NMR shift and spin-lattice relaxation results below 200 K reveal a Korringa-like response indicating heavily-doped p-type behavior due to native defects. Above 280 K, this converts to an activated behavior, indicating the presence of an impurity band, empty at low temperatures, which is located around 0.03 eV above the valence band maximum.
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