Pressure-induced phase transition and fracture in α-MoO₃ nanoribbons

MoO₃ nanoribbons were studied under different pressure conditions ranging from 0 to 21GPa at room temperature. The effect of the applied pressure on the spectroscopic and morphologic properties of the MoO₃ nanoribbons was investigated by means of Raman spectroscopy and scanning electron microscopy techniques. The pressure dependent Raman spectra of the MoO₃ nanoribbons indicate that a structural phase transition occurs at 5GPa from the orthorhombic α-MoO₃ phase (Pbnm) to the monoclinic MoO₃-II phase (P2₁/m), which remains stable up to 21GPa. Such phase transformation occurs at considerably lower pressure than the critical pressure for α-MoO₃ microcrystals (12GPa). We suggested that the applanate morphology combined with the presence of crystalline defects in the sample play an important role in the phase transition of the MoO₃ nanoribbons. Frequencies and linewidths of the Raman bands as a function of pressure also suggest a pressure-induced morphological change and the decreasing of the nanocrystal size. The observed spectroscopic changes are supported by electron microscopy images, which clearly show a pressure-induced morphologic change in MoO₃ nanoribbons.