Sheet superconductivity in WO3-x:: crystal structure of the tetragonal matrix

Sheet conductivity was found in oxygen reduced WO3-x. The sheets are aligned along the twin boundaries of the unreduced starting material (beta-WO3). The bulk transforms during the oxygen loss to a WO3-x, phase with tetragonal crystal structure. The space group is P (4) over bar 2(1)m with lattice parameters a = 0.739 nm and c = 0.388 nm. The perovskite-like structure contains distorted octahedra with W-O distances between 0.17 nm and 0.218 nm.