<jats:title>Abstract</jats:title><jats:p>Most solid-state materials are composed of p-block anions, only in recent years the introduction of hydride anions (1s<jats:sup>2</jats:sup>) in oxides (e.g., SrVO<jats:sub>2</jats:sub>H, BaTi(O,H)<jats:sub>3</jats:sub>) has allowed the discovery of various interesting properties. Here we exploit the large polarizability of hydride anions (H<jats:sup>–</jats:sup>) together with chalcogenide (Ch<jats:sup>2–</jats:sup>) anions to construct a family of antiperovskites with soft anionic sublattices. The M<jats:sub>3</jats:sub>HCh antiperovskites (M = Li, Na) adopt the ideal cubic structure except orthorhombic Na<jats:sub>3</jats:sub>HS, despite the large variation in sizes of M and Ch. This unconventional robustness of cubic phase mainly originates from the large size-flexibility of the H<jats:sup>–</jats:sup> anion. Theoretical and experimental studies reveal low migration barriers for Li<jats:sup>+</jats:sup>/Na<jats:sup>+</jats:sup> transport and high ionic conductivity, possibly promoted by a soft phonon mode associated with the rotational motion of HM<jats:sub>6</jats:sub> octahedra in their cubic forms. Aliovalent substitution to create vacancies has further enhanced ionic conductivities of this series of antiperovskites, resulting in Na<jats:sub>2.9</jats:sub>H(Se<jats:sub>0.9</jats:sub>I<jats:sub>0.1</jats:sub>) achieving a high conductivity of ~1 × 10<jats:sup>–4</jats:sup> S/cm (100 °C).</jats:p>
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