Ca1.5 Eu3Sn0.5 O7: a calcium europium tin oxide with a novel structure.

A new quaternary compound in the Ca-Eu-Sn-O system, namely calcium europium tin heptaoxide, Ca1.5 Eu3Sn0.5 O7, was prepared by solid-state reaction at 2073 K. All atoms in the structure are on 4i special positions (on mirrors) in space group C2/m. Ca/Eu sites are situated within two O octahedra and within two sevenfold coordination sites surrounded by O-capped trigonal prisms. A Ca/Eu/Sn site is coordinated by five O atoms. The structural formula can be represented as (Ca0.28 Eu0.72)(Ca0.16 Eu0.84)(Ca0.46 Eu0.54)(Ca0.28 Eu0.72)(Ca0.32 Eu0.18 Sn0.50)O7. The crystal structure is a new type and is related to the structure of B-form Eu2O3.