Structure and stability of monazite- and zircon-type LaVO4 under hydrostatic pressure

Pure monazite ( m )- and zircon ( t )-type LaVO 4 and LaVO 4 :Eu 3+ were successfully synthesized by a hydrothermal method . The high pressure behavior of m - and t -LaVO 4 nanoparticles has been investigated using Raman scattering techniques at room temperature. Raman measurements reveal a slight change for m -LaVO 4 at 11.2   GPa because of an isostructural phase transition. However, striking changes in Raman spectra indicate a pressure-induced irreversible phase transition from the zircon to monazite structure for t -LaVO 4 at around 5.9   GPa. The evolution of the luminescence spectra of t -LaVO 4 :Eu 3+ has also been studied during the pressure-induced phase transition. It is observed that pressure has a great influence on the fluorescence intensity and the energy levels, which allows a more in-depth understanding of the nature of the pressure-induced phase transition for t -LaVO 4 . This result further confirms the conclusion that zircon-type RVO 4 compounds with larger rare-earth cations will experience zircon to monazite phase transition.