LEED study of Na xWO 3 tungsten bronze: structural relaxation of a perovskite surface

Abstract

We have performed a low energy electron diffraction study of the sodium tungsten bronze, Na x WO 3 x = 0.8, surface. Temperature dependent changes of both polished and cleaved surfaces indicate structural phase transitions of the surface structure, and reflect the general trend in structural phase transitions of the bulk. Surface phase transitions take place, however, at higher temperatures, indicating a relaxation of the surface of this perovskite structure. In addition, sodium ordering in non-equivalent sites modifies the LEED patterns. We show that our description also applies to the data previously reported by other groups covering a larger range of sodium concentration x. Our measurements indicate that the surface structure is sensitive to sample heating, displaying an irreversible change near 600°C.