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In this work, extensive thermo-Raman investigations have been carried out on a γ(L)-Bi2MoO6 sample (`(L)' indicating the low-temperature polymorph) in an effort to gain an understanding of the structural evolution and phase transformation involved during a dynamical thermal process. The room temperature Raman spectrum of the γ(L)-Bi2MoO6 phase indicated the presence of corner-sharing distorted MoO6 octahedra. The spectral variations, shift in the band positions, decrease in intensities and broadening of the Mo-O modes observed in the thermo-Raman spectra and the thermal evolution of the Mo-O bonds in the temperature interval from 25 to 610 °C strongly suggest that the transformation from the γ(L)-Bi2MoO6 to the γ(I)-Bi2MoO6 phase (`(I)' indicating the intermediate-temperature polymorph) involves a gradual anisotropic thermal response of Mo-O bonds initially, upon heating, and further appreciable increase in the octahedral distortion from 310 °C onwards - until the structure is on the verge of becoming composed of distorted tetrahedra. The spectral variation in the thermo-Raman spectra observed for the transformations to γ(H)-Bi2MoO6 (`(H)' indicating the high-temperature polymorph) starting at around 620 °C and ending at 660 °C revealed the sluggish nature of the transformations and also clearly indicated the transformation from highly distorted MoO6 octahedra to distorted tetrahedra. The comparison of the profile of the Raman spectrum of the γ(H)-Bi2MoO6 phase measured at 720 °C and that measured after cooling down to 25 °C clearly rules out the possibility of the formation of a β-Bi2Mo2O9} phase structure consisting of Mo6+ in tetrahedral coordination at high temperature.

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