Preparation and structure of mixed tungsten bronzes containing tin and europium

An isothermal section has been established for the system Eu_xWO₃Sn_yWO₃ at 1000°C from X-ray powder and single-crystal data and Mössbauer spectroscopy and chemical analyses. A single-phase region with the (12 × 3) tetragonal structure has been established. Single-crystal X-ray analysis shows that the Sn and Eu occupy pentagonal tunnel sites. Mössbauer spectroscopy shows that both Sn(II) and Eu(II) are present. The extent of the single-phase field is controlled by two factors: First, the ratio $\text{Eu}\text{Sn}$ must be <1, and second, the supernumerary electron concentration per WO₃ must be <0.6.