Double half-Heusler alloys <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:msub> <mml:mi>X</mml:mi> <mml:mn>2</mml:mn> </mml:msub> <mml:msub> <mml:mi>Ni</mml:mi> <mml:mn>2</mml:mn> </mml:msub> <mml:mi>InSb</mml:mi> </mml:math> ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mi>X</mml:mi> </mml:math> = <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mi>Zr</mml:mi> </mml:math> , <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mi>Hf</mml:mi> </mml:math> ) with promising thermoelectric performance: The role of varying structural phases

Abstract

Double half-Heusler (HH) alloys are a new class of compounds that can be seen as transmuted versions of two single half-Heusler alloys with higher flexibility of tunability of their properties. Here, we report a detailed study of the thermoelectric (TE) properties of two double HH alloys ${X}_{2}{\mathrm{Ni}}_{2}\mathrm{InSb}$ ($X$ = $\mathrm{Hf}$, $\mathrm{Zr}$), using first-principles calculation. These alloys exhibit a rich phase diagram with the possibility of tetragonal, cubic, and solid-solution phases. As such, a comparative study of the TE properties of all these phases is highly desired. The simulated band gap, obtained using a hybrid functional, of the ordered phase of ${\mathrm{Hf}}_{2}{\mathrm{Ni}}_{2}\mathrm{InSb}$ and ${\mathrm{Zr}}_{2}{\mathrm{Ni}}_{2}\mathrm{InSb}$ lies in the range 0.24--0.4 and 0.17--0.59 eV, respectively, while, for the disordered phase, it lies in between 0.05 and 0.06 eV. A simulated TE figure of merit ($ZT$) as high as 2.02 and 2.45 is obtained for ${\mathrm{Hf}}_{2}{\mathrm{Ni}}_{2}\mathrm{InSb}$ and ${\mathrm{Zr}}_{2}{\mathrm{Ni}}_{2}\mathrm{InSb}$, respectively. In both compounds, electronic transport plays the dominant role in achieving the promising $ZT$ values. We believe this study will attract the attention not only of experimentalists but also of theoreticians from the thermoelectric community to further investigate similar double HH alloys.

Topics & Concepts