Crystal chemistry and subsolidus phase relations in the system EuWO

Abstract Crystal chemistry and subsolidus phase relations in a portion of the system EuWO have been investigated. The stoichiometry and symmetry determined for compounds on the Eu2O3WO3 join are: Eu6WO12, cubic or tetragonal depending on the conditions of preparation—structure related to fluorite; Eu14W4O33, pseudorhombohedral; Eu2WO6, monoclinic—structure related to scheelite; Eu2W2O9, monoclinic—isostructural with Pr2W2O9; Eu2W3O12, monoclinic—structure also related to scheelite. The only divalent europium tungsten oxide, EuWO4, had the tetragonal scheelite structure. Because of the structural similarity of EuWO4 and Eu2W3O12 (Eu0.67WO4), there was actually a limited scheelite structure solid solution EuxWO4 (x ≈ 1 → 0.77) between them. A cubic europium tungsten bronze, EuxWO3, was found for x ≈ 0.07 → 0.15. The compatibility relations among all of these phases and those on the EuO and WO binary system are presented in a subsolidus phase diagram.