Influence of anharmonicity on the thermoelectric properties of alkali antimonide compounds <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:msub> <mml:mi>M</mml:mi> <mml:mn>3</mml:mn> </mml:msub> <mml:mi>Sb</mml:mi> </mml:math> ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mi>M</mml:mi> </mml:math> = <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mi>Na</mml:mi> </mml:math> , <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">K</mml:mi> </mml:mrow> </mml:mrow> </mml:math> , <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mi>Rb</mml:mi> </mml:math> , <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mi>Cs</mml:mi> </mml:math> )
Peipei Liu, Yinchang Zhao, Jun Ni, Zhenhong Dai
Abstract
This study systematically explores the mechanical, transport, and thermoelectric properties of the alkali antimonide compounds ${M}_{3}\mathrm{Sb}$ ($M$ = $\mathrm{Na}$, $\mathrm{K}$, $\mathrm{Rb}$, $\mathrm{Cs}$) using first-principles calculations and the Boltzmann transport equation. We found that considering quartic anharmonic effects leads to temperature-dependent phonons undergoing a frequency shift and overall phonon spectrum hardening, thereby increasing the phonon group velocity. Additionally, this study reveals that alkali-metal atoms play an important role in the phonon frequency of ${M}_{3}\mathrm{Sb}$ ($M$ = $\mathrm{Na}$, $\mathrm{K}$, $\mathrm{Rb}$, $\mathrm{Cs}$). The quartic anharmonicity strengthens as the mass of the alkali-metal atom increases. Moreover, as the atomic number of alkali-metal atoms increases, the interaction between atoms weakens, resulting in a gradual decrease in bulk modulus ($B$), shear modulus ($G$), and Young's modulus ($E$). We also observe that, beyond 400 K, the lattice thermal conductivity ${\ensuremath{\kappa}}_{L}$ of ${\mathrm{Rb}}_{3}\mathrm{Sb}$ is lower than that of ${\mathrm{Cs}}_{3}\mathrm{Sb}$, which is mainly attributed to the larger scattering rate of ${\mathrm{Rb}}_{3}\mathrm{Sb}$. By considering various scattering mechanisms, we obtain reasonable electron relaxation times and electron transport properties. Because of the large electronic dispersion band at the conduction-band minimum, $p$-type ${M}_{3}\mathrm{Sb}$ exhibits high electron mobility. Finally, owing to the low lattice ${\ensuremath{\kappa}}_{L}$ and good power factor, these four $p$-type alkali antimonide compounds demonstrate excellent thermoelectric performance.