Effects of high-pressure on the structural, vibrational, and electronic properties of monazite-type PbCrO 4

Abstract

We have performed an experimental study of the crystal structure, lattice dynamics, and optical properties of PbCrO 4 (the mineral crocoite) at ambient and high pressures. In particular, the crystal structure, Raman-active phonons, and electronic band gap have been accurately determined. X-ray-diffraction, Raman, and optical absorption experiments have allowed us also to completely characterize two pressure-induced structural phase transitions. The first transition is from a monoclinic structure to another monoclinic structure. It maintains the symmetry of the crystal but has important consequences in the physical properties; among others, a band-gap collapse is induced. The second one involves an increase of the symmetry of the crystal, a volume collapse, and probably the metallization of PbCrO 4. The results are discussed in comparison with related compounds, and the effects of pressure in the electronic structure are explained. Finally, the room-temperature equation of state of the low-pressure phases is also obtained. © 2012 American Physical Society.