Domain structures of sodium tungsten bronzes,NaxWO3 (0.4 < x < 1)

Optical-microscope observations with polarized light have shown that the birefringent, twin-domain structure of sodium tungsten bronzes is exhibited by Na-deficient, epitaxial surface films and hence is not a bulk property as had been suggested elsewhere. The film is translucent, 10^-2-10^-3 mm thick or less, and often laminates to a multi-film layer The domain boundaries are sensitive to lateral stress and, apparently, to minute changes in the substrate structure. These and related properties of the film and the substrate are presented.