High-Temperature Incommensurate-to-Commensurate Phase Transition in the Bi2MoO6 Catalyst

The temperature-dependent behavior of the low- and intermediate-temperature phases of gamma-Bi2MoO6 were investigated. As revealed by high-resolution neutron and synchrotron powder diffraction as well as electron diffraction, the low-temperature Aurivillius phase shows a previously undetected incommensurate modulation along the pseudo-tetragonal a (qa= 0.5626(2)) and c (qc=0.2844(2)) axes. A reversible incommensurate-to-commensurate phase transition to the intermediate-temperature phase occurs near 840 K, before irreversibly transforming near 880 K into the fluorite-related high-temperature polymorph described in detail by two of us in an earlier study (Buttrey et al., J. Solid State Chem. 111, 118 -127 (1994)).