A series of aluminum tungsten oxides crystallizing in a new ReO3-related structure type

A series of new aluminum tungsten oxides with the general formula Al₄W_2nO_6n+2 (n=4-7) was found and structurally characterized by electron diffraction, high-resolution transmission electron microscopy (HRTEM) and high angle annular dark field scanning transmission electron microscopy (HAADF-STEM). The structural model for Al₄W₁₀O₃₂ (I4/mmm (space group no. 139); a≈0.375, c≈3.95 nm) consists of slabs of 5×∞×∞] corner-sharing WO₆ octahedra that are connected via edge-sharing to AlO₆ octahedra. Simulated HRTEM images agree well with the experimental ones and thus support the proposed structural model. The connection between adjacent slabs of WO₃ via AlO₆ octahedra represents a novel variant of crystallographic shear operation for ReO₃-type structures. The crystallites display a wide range of stacking sequences that are frequently intergrown with each other.