Atomic-scale images of the (001) surface of the monoclinic oxide were obtained by means of scanning tunnelling microscopy. The termination of the surface WO2 plane by half of a monolayer of O ions gave a surface periodicity which was 2 times that of the underlying ReO3-like framework. An additional periodicity was introduced by tilting of the WO6 octahedra to produce alternately long and short O-O separations along the [110] direction. This produced a (2 x 2) superstructure which approximated to the space group, c2mm. Prominent defect lines which were observed at the surface were attributed to missing O ions.

F.H.Jones, K.Rawlings, J.S.Foord, P.A.Cox, R.G.Egdell, J.B.Pethica, B.M.R.Wanklyn: Physical Review B, 1995, 52[20], R14392-5