Sr1−xKxSi1−yGeyO3−0.5x: a new family of superior oxide-ion conductors

Abstract

Monoclinic SrMO₃ (M = Si or Ge) contains (001) planes of M₃O₉ units of three corner shared MO₄ coplanar complexes separated by close-packed planes of Sr²⁺ ions each coordinated, top and bottom, by three terminal oxygen on three different M₃O₉ units. Substitution of K⁺ for Sr²⁺ introduces terminal-oxygen vacancies that are either not accommodated by corner sharing with a neighboring M₃O₉ unit, apparently because of steric hindrance by the large Sr²⁺ and K⁺ ions, or are accommodated by a distortion that creates an interstitial mobile oxide ion. Stabilization of a terminal-oxygen vacancy in a tetrahedral anion complex by steric hindrance in Sr_1−xK_xSi_1−yGe_yO_3−0.5x represents a new design principle for superior oxide-ion electrolytes at intermediate temperatures.