Superstructures In The Scheelite-Type Rare Earth Doped Tungstate Phases

The aim of the present work deals with the TEM study of scheelite related AWO4 compounds [1] showing modulated microstructures not revealed with synchrotron XRD investigations. These materials have potential applications in many fields such as photoluminescence, microwave, scintillator materials, humidity sensors and catalysis. Rare earth (RE) tungstate RE2(WO4)3 crystal phases are based on a cation-deficient superstructure of CaWO4. Cation substitution of RE are investigated in order to correlate the microstructure to physical properties especially for new potential applications in white-LEDs and lasers. In our study, a two-phase powder containing the monoclinic Ce2(WO4)3 and orthorhombic Ce10W22O81 structures [2], was obtained by complexing method using EDTA and citrate ions. In the latter phase, PED and HRTEM investigations showed a C2/c superspace group (SSG) doubling the smallest a cell parameter [3]. Additionally, another cerium tungstate structure substituted with strontium cations was also investigated revealing a (3+2)D incommensurately modulated structure.