Sr_1/2Ce_5/14□_1/7WO₄: a new modulated ternary scheelite compound

For the first time, a ternary tetragonal scheelite structure tungstate with strontium and cerium cations, (Sr,Ce)WO₄, was synthesized. As much as 35% Ce could be inserted into the structure, leaving of the (Sr,Ce) cation sites vacant. Partial ordering of Sr and Ce, with atomic displacements, were shown by high-resolution electron microscopy. Two-dimensional incommensurate modulations occur in this material, in small domains 20 nm in size. The band gap of this compound is significantly lower than the band gap of SrWO₄ and this was related to the distortions of WO₄ and (Sr,Ce)O₈ polyhedra. The band gap value of 3.2 eV makes Sr_1/2Ce_5/14□_1/7WO₄ a promising candidate for violet luminescence.