Amorphous–crystalline transition studied in hydrated MoO3

In this work we study the thermal behavior of hydrated MoO3 synthesized via acidification of sodium molybdate. MoO3·nH2O (n = 1.4) amorphous compound was heated in air at increasing temperatures in order to obtain the crystalline MoO3 phase. We have studied the structural changes as a function of annealing temperature by Raman spectroscopy. A statistical study to determine the average size of the crystallites at each annealing step has been realized by scanning electron microscopy. Results show that the hydrated MoO3·1.4H2O glass transforms in an amorphous MoO3·0.7H2O phase prior to its crystallization, while the sample heated at 500 °C crystallizes into the orthorhombic α-MoO3 phase with micro-crystallites having an average size of 6.8 μm.