Carrier concentration is an important parameter for improving the thermoelectric (TE) properties of half-Heusler alloys, which can be achieved by defect engineering. In the present work, we studied the electronic structure and TE properties of TiNiSn with self-defects by using first-principles calculation. The self-defects include vacancies, substitutions, and interstitials, and all these systems were studied on the basis of defect formation energy. The stability of defect configurations showed that the Ni-vacancy (Ni-vac), Ti substitution at a Ni site (TiNi), Sn substitution at Ti and Ni sites (SnTi, SnNi), Ti-interstitial (Ti-int), and Ni-interstitial (Ni-int) are the most favorable defects. The self-defects were found to create an electron pocket in the density of states at the Fermi energy (DOS(EF)), except for the Ni-vac. Further, the electron concentration and specific heat were significantly increased by the self-defects. Ni-vac, TiNi, and SnNi showed a large power factor in comparison to pristine TiNiSn due to the high electrical conductivity. Ni-vac and SnNi showed a high TE performance in the intermediate and high temperature range, which would make them excellent TE candidates for a variety of applications.
This work was financially supported by the Thailand Research Fund (TRF) through the Royal Golden Jubilee (RGJ) Ph.D. Program (Grant No.PHD/0195/2558). We would like to thank Asst. Prof. Dr. Pornjuk Srepusharawoot, Department of Physics, Faculty of Science, Khon Kaen University, Thailand, for supporting the MSNcluster computational and with the financial support of the Thailand Research Fund: RSA6180070.
C. Fu, S. Bai, Y. Liu, Y. Tang, L. Chen, X. Zhao, and T. Zhu, Nat. Commun. 6, 8144 (2015).CrossRefGoogle Scholar