KSbO(Ge0.32Si0.68)O-4, a KTP isomorph

Journal article, 2001

A structural model of potassium antimony germanate/silicate (0.32/0.68), KSbO(Ge0.32Si0.68)O-4, has been determined at room temperature. KSbO(Ge0.32Si0.68)O-4 belongs to the KTiOPO4 (KTP) isomorphic family and is composed of SbO6 octahedra (site symmetry (1) over bar and 2) arranged in helical chains bridged by (Ge/Si)O-4 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) Angstrom apart, with an indication of a third potassium position between them. At room temperature, KSbO(Ge0.32Si0.68)O-4 crystallizes in the paraelectric phase of space group Pnan. This phase is found at elevated temperatures for almost all KTiOPO4 isomorphic compounds and KSbO(Ge0.32Si0.68)O-4 is the second isomorph that is paraelectric at room temperature.