SCANNING-TUNNELING-MICROSCOPY AND CRYSTAL-CHEMICAL MODELS OF THE NA0.82WO3(001) SURFACE

The cleaved (001) surface of Na0.82WO3, a cubic tungsten bronze, has b een imaged with a scanning tunneling microscope. The periodicity of th e atomic-scale contrast in these images can be described by a rectangu lar cell with a equal to the bulk lattice parameter and b = 2a. A crys tal chemical model for the surface structure, based on the bond valenc e and distance-least-squares methods, has been used to show that an or dered distribution of Na in the near surface region could lead to atom ic relaxations and the observed 1 x 2 structure. Based on the atomic p ositions predicted by this model, constant current STM images have bee n calculated for a variety of parameters. The experimental observation s are consistent with simulated images of the W-O terminated surface. (C) 1994 Academic Press, Inc.