Fully Ab-Initio Determination of the Thermoelectric Properties of Half-Heusler NiTiSn: Crucial Role of Interstitial Ni Defects

Abstract

For thermoelectric applications, ab initio methods generally fail to predict the transport properties of the materials because of their inability to predict properly the carrier concentrations that control the electronic properties. In this work, a methodology to fill in this gap is applied on the NiTiSn half Heusler phase. For that, we show that the main defects act as donor of electrons and are responsible of the electronic properties of the material. Indeed, the presence of Nii interstitial defects explains the experimental valence band spectrum and its associated band gap reported in the literature. Moreover, combining the DOS of the solid solutions with the determination of the energy of formation of charged defects, we show that Nii defects are also responsible of the measured carrier concentration in experimentally supposed “pure” NiTiSn compounds. Subsequently the thermoelectric properties of NiTiSn can be calculated using a fully ab initio description and an overall correct agreement with experiments is obtained. This methodology can be extended to predict the result of extrinsic doping and thus to select the most efficient dopant for specific thermoelectric applications.

Electronic Structure and Thermoelectric Properties of Co‐, Fe‐, Mn‐, and Cr‐Doped Ba2LuTaO6 from Spin‐Polarized Calculations

“…We observe that at temperatures below room temperature, the ZT value varies from 0.75 to 0.99 for Ba 2 LuTa 0.75 TM 0.25 O 6 materials. Thus, in comparison with other values of the figure of merit at room temperature reported in previous theoretical and experimental studies, such as NiTiSn [ 68 ] and CuI–Pb co‐doped Bi 2 Te 3 ( ZT = 0.96), [ 69 ] it can be concluded that this material can be regarded as a suitable material for application in the thermoelectric cooling industry.…”

Manipulation of Ni Interstitials for Realizing Large Power Factor in TiNiSn‐Based Materials

“…In this half‐Heusler material, Ni plays a unique role in either phonon or electron transport. Based on first‐principle calculations, interstitial Ni atoms are energetically more favorable than other types of defects . Neutron diffraction results have also confirmed partial occupancy of the 4d position by a small amount of Ni in the 1:1:1 stoichiometric TiNiSn …”

Decisive role of interstitial defects in half-Heusler semiconductors: An ab initio study

“…It has been speculated that slight change in alloy composition in the experimental samples due to point defects may explain this deviation from the usual trend observed in semiconductors [57,64,65]. While external doping is the commonly employed point defect engineering strategy for tailoring carrier concentration and mobility [44][45][46][88][89][90][91][92][93][94], intrinsic point defects can also modify electronic structure, carrier concentration, and hence transport properties of half-Heusler alloys [95][96][97][98][99][100][101][102]. The high-resolution angle-resolved photoemission spectroscopy (ARPES) measurements can be used to gain insights into the defect-induced changes in the electronic structure [99,103].…”