Pressure-Induced Phase Transformations of Zircon-Type LaVO₄ Nanorods

A combination of synchrotron powder X-ray diffraction (XRD) and Raman spectroscopy has been used to study high-pressure behavior of the zircon-type LaVO 4 nanorods. In situ high-pressure XRD results identified an irreversible zircon-to-monazite phase transition at ∼5 GPa and a reversible transition to an undetermined second high-pressure phase (phase III) at ∼12.9 GPa. Through Le Bail refinements of the XRD patterns with zircon-type structure, we show that the zircon-type LaVO 4 nanorods possess the smallest bulk modulus among zircon-type rare-earth orthovanadates. Furthermore, negative pressure coefficients of external translational T(E g ) and internal υ 2 (B 2g ) bending modes have been observed in Raman measurements. The Raman spectra of phase III with distinctive features have been fully recorded for the first time, and a related structure associated with a coordination increase for V is suggested in terms of the postmonazite phase in LaVO 4 nanorods. Finally, analysis of the transmission electron microscopy both before and after compression indicates that a large number of nanorods can be recovered in the quenched samples, allowing us to verify the orientation relationship for zircon-to-monazite phase transformation.