The morphological evolution of the Bi_2Mo_3O_(12)(010) surface in air-H_2O atmospheres

摘要

Atomic force microscopy (AFM) has been used to examine the morphological evolution of the Bi_2Mo_3O_(12)(010) surface at 400-600 deg C in dry air and air-2.3% H_2O. The (010) cleavage surface is characterized by atomically flat terraces separated by straight steps that are integer multiples of b/2 (5.75 A) in height. During treatments at or above 500 deg 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% H_2O, steps are etched with preference to terraces,and this leads to step recession as well as the formation of Bo-rich deposits. Mo volatilization proceeds at an enhanced rate in air-2.3% H_2O and culminates in the nucleation and growth of Bi_2MoO_6 and Bi_2Mo_2O_9 precipitates at 500 and 600 deg C, respectively.