Anomalous electronic and thermoelectric transport properties in cubic Rb3AuO antiperovskite

Abstract

We use first-principles calculations combined with self-consistent phonon (SCP) theory, electron-phonon ($e\ensuremath{-}ph$) coupling, and the Boltzmann transport equation (BTE) to investigate the electronic and thermoelectric transport properties in the cubic ${\mathrm{Rb}}_{3}\mathrm{AuO}$ antiperovskite with strongly cubic and quartic lattice anharmonicity. The combination of SCP theory and Wannier-Fourier interpolation is used to calculate the $e\ensuremath{-}ph$ coupling due to the failure of density functional perturbation theory in solving $e\ensuremath{-}ph$ matrix elements for a strongly anharmonic crystal. Our results exhibit that a high electron mobility ${\ensuremath{\mu}}_{e}$, e.g., $\ensuremath{\sim}454\phantom{\rule{0.28em}{0ex}}{\mathrm{cm}}^{2}/\mathrm{Vs}$ at $300\phantom{\rule{0.28em}{0ex}}\mathrm{K}$ from the iterative BTE solution, and a relatively weak temperature dependence of ${\ensuremath{\mu}}_{e}\ensuremath{\propto}{T}^{\ensuremath{-}1.1}$ are obtained in the $n$-type cubic ${\mathrm{Rb}}_{3}\mathrm{AuO}$. We demonstrate that the coupling between electrons and polar optical phonons is responsible for the good charge transport, which, along with the high thermopower deriving from a light and threefold degenerate conduction-band pocket around the $X$ point, leads to a very high power factor reaching $5.5\phantom{\rule{4pt}{0ex}}\mathrm{mW}/{\mathrm{mK}}^{2}$ at $800\phantom{\rule{0.28em}{0ex}}\mathrm{K}$. Meanwhile, a low lattice thermal conductivity and an undersized Lorenz number that signifies a resulting low electron thermal conductivity are also detected. As a result, a good thermoelectric performance with a figure of merit $ZT\ensuremath{\sim}1.02$ at $300\phantom{\rule{0.28em}{0ex}}\mathrm{K}$ and an anomalously high $ZT\ensuremath{\sim}3.02$ at $800\phantom{\rule{0.28em}{0ex}}\mathrm{K}$ is captured in the $n$-type cubic ${\mathrm{Rb}}_{3}\mathrm{AuO}$. This finding breaks the long-term record of $ZT<3$ in most of the reported bulk thermoelectric materials to date, and illustrates that the cubic ${\mathrm{Rb}}_{3}\mathrm{AuO}$ is an excellent candidate for thermoelectric applications.