KSbO(Ge0.32Si0.68)O4, a KTP isomorph

A structural model of potassium antimony germanate/silicate (0.32/0.68), KSbO(Ge_0.32Si_0.68)O₄, has been determined at room temperature. KSbO(Ge_0.32Si_0.68)O₄ belongs to the KTiOPO₄ (KTP) isomorphic family and is composed of SbO₆ octahedra (site symmetry and 2) arranged in helical chains bridged by (Ge/Si)O₄ tetrahedra. Germanium and silicon have a similar distribution in the crystallographically independent tetrahedra (site symmetry 2). The structure contains large cavities occupied by the K atom. Two partially occupied potassium positions have been identified 1.273 (8) Å apart, with an indication of a third potassium position between them. At room temperature, KSbO(Ge_0.32Si_0.68)O₄ crystallizes in the paraelectric phase of space group Pnan. This phase is found at elevated temperatures for almost all KTiOPO₄ isomorphic compounds and KSbO(Ge_0.32Si_0.68)O₄ is the second isomorph that is paraelectric at room temperature.