Transition metal compound surfaces I: The cubic sodium tungsten bronze (Na_xWO₃) surface

The two dimensional surface structure and the surface chemical composition of (100) cubic sodium tungsten bronze (Na_xWO₃) has been investigated using low energy electron diffraction and Auger electron spectroscopy. Single crystals with bulk x values ranging from 0.5 to 0.9 were examined. The (100) surface exhibits the square symmetry of the WO₃ lattice, with fractional order features corresponding to ordered sodium row structures which depend on the crystal x value. Auger spectra support covalent bonding models of these materials, in which sodium contributes little to the lattice binding. LEED and Auger results indicate sodium depletion in the surface region. In addition, evidence of a sodium order/disorder transition in the surface region is obtained.