Enhancement of thermoelectric efficiency of<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>T</mml:mi><mml:mtext>−</mml:mtext><mml:msub><mml:mrow><mml:mi>HfSe</mml:mi></mml:mrow><mml:mn>2</mml:mn></mml:msub></mml:math>via nanostructuring
Elif Ünsal, R. T. Senger, Hâldun Sevinçli
Abstract
In this work, ab initio calculations based on density functional theory and the Landauer formalism are carried out to investigate ballistic thermoelectric properties of $T\text{\ensuremath{-}}\mathrm{Hf}{\mathrm{Se}}_{2}$ nanoribbons (NRs). The zigzag-edged NRs are metallic, and they are not included in this study. The armchair NRs possess two types of edge symmetries depending on the number of atoms present in a row; odd-numbered NRs have mirror symmetry, whereas the even-numbered NRs have glide reflection symmetry. The armchair-edged NRs are dynamically stable and show semiconducting properties with varying band gap values in the infrared and visible regions. Detailed transport analyses show that the $n$-type Seebeck coefficient and the power factor differ because of the structural symmetry, whereas the $p$-type thermoelectric coefficients are not significantly influenced. It is shown that the phonon thermal conductance is reduced to a third of its two-dimensional value via nanostructuring. The $p$-type Seebeck coefficient and the power factor for $T$-phase $\mathrm{Hf}{\mathrm{Se}}_{2}$ are enhanced in NRs. We report that the $p$-type $ZT$ value of $\mathrm{Hf}{\mathrm{Se}}_{2}$ NRs at 300 and 800 K are enhanced by factors of 4 and 3, respectively.