Phonon properties, polymorphism, and amorphization ofDy2Mo4O15under high hydrostatic pressure

${\text{Dy}}_{2}{\text{Mo}}_{4}{\text{O}}_{15}$ crystal was investigated by high-pressure Raman spectroscopy experiments. The assignment of vibrational modes at ambient pressure was made based on lattice-dynamics calculations and the results helped us also to discuss high-pressure transformations observed in this material. A pressure-induced structural phase transition was observed at about 2.0 GPa. This transition is associated with significant rearrangement of the molybdenum-oxygen sublattice and an increase in the molybdenum-oxygen coordination most likely changing from tetrahedral to pentagonal. The bond compressibility, related to the Mo-O bonds, were estimated for both $P{2}_{1}/c$ and high-pressure phase. Upon further increase in pressure ${\text{Dy}}_{2}{\text{Mo}}_{4}{\text{O}}_{15}$ exhibits irreversible amorphization above 4.7 GPa. The irreversible character of this transformation points out to either chemical decomposition or crystallographic transformation as a cause of this amorphization process. Our analysis suggests that the amorphization of ${\text{Dy}}_{2}{\text{Mo}}_{4}{\text{O}}_{15}$ may be most likely attributed to a chemical decomposition.