Enhancing the Thermoelectric Performance of Self-Defect TiNiSn: A First-Principles Calculation

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.