The morphological evolution of the Bi2Mo3O12(010) surface in air–H2O atmospheres

Atomic force microscopy (AFM) has been used to examine the morphological evolution of the Bi2Mo3O12(010) surface at 400–600 °C in dry air and air–2.3% H2O. The (010) cleavage surface is characterized by atomically flat terraces separated by straight steps that are integer multiples of b/2 (5.75 Å) in height. During treatments at or above 500 °C, the surface is etched due to the volatilization of Mo. In dry air, etching affects both steps and flat terraces and results in step recession, the development of half-unit-cell (b/2) step loops (pits and islands), and the accumulation of Bi-rich surface deposits. In air–2.3% H2O, steps are etched with preference to terraces, and this leads to step recession as well as the formation of Bi-rich deposits. Mo volatilization proceeds at an enhanced rate in air–2.3% H2O and culminates in the nucleation and growth of Bi2MoO6 and Bi2Mo2O9 precipitates at 500 and 600 °C, respectively.