Superionicity of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msup><mml:mrow><mml:mi mathvariant="normal">H</mml:mi></mml:mrow><mml:mrow><mml:mi>δ</mml:mi><mml:mo>−</mml:mo></mml:mrow></mml:msup></mml:math> in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>LaH</mml:mi><mml:mn>10</mml:mn></mml:msub></mml:math> superhydride
Maélie Caussé, Grégory Geneste, Paul Loubeyre
Abstract
Recent computational studies have successfully predicted the dramatic uptake of hydrogen by metals under pressure leading to the formation of superhydrides, now ubiquitously observed. ${\mathrm{LaH}}_{10}$ exemplifies the properties of these novel H-rich compounds, some of which form a novel class of superconducting materials. We show here another remarkable property for superhydrides, namely, ${\text{H}}^{\ensuremath{\delta}\ensuremath{-}}$ superionicity. By means of ab initio molecular dynamics simulations in ${\mathrm{LaH}}_{10}$, an exceptionally high hydride $({\mathrm{H}}^{\ensuremath{\delta}\ensuremath{-}})$ diffusion coefficient is calculated at high temperature, with $D=1.7\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}\phantom{\rule{0.28em}{0ex}}\mathrm{cm} {}^{2}$/s at 170 GPa and 1500 K, corresponding to an ionic conductivity of $\ensuremath{\sigma}=0.9\phantom{\rule{0.16em}{0ex}}{(\mathrm{\ensuremath{\Omega}}\phantom{\rule{0.16em}{0ex}}\mathrm{cm})}^{\ensuremath{-}1}$ and so indicating a superionic phase. The superionic phase is surprisingly stable up to 2500 K and its melting temperature is remarkably high, similar to that of pure La. The connected path for the hydride ionic diffusion is disclosed, with the H sublattice keeping its clathrate structure. The conductivity properties of ${\mathrm{LaH}}_{10}$ are discussed in relation to the recently discovered family of compounds showing fast pure hydride ions transport.