Electronic, Vibrational, and Structural Properties of the Natural Mineral Ferberite (FeWO): A High-Pressure Study.

This paper reports an experimental high-pressure study of natural mineral ferberite (FeWO) up to 20 GPa using diamond-anvil cells. First-principles calculations have been used to support and complement the results of the experimental techniques. X-ray diffraction patterns show that FeWO crystallizes in the wolframite structure at ambient pressure and is stable over a wide pressure range, as is the case for other wolframite AWO (A = Mg, Mn, Co, Ni, Zn, or Cd) compounds. No structural phase transitions were observed for FeWO, in the pressure range investigated. The bulk modulus ( = 136(3) GPa) obtained from the equation of state is very close to the recently reported value for CoWO (131(3) GPa). According to our optical absorption measurements, FeWO has an indirect band gap that decreases from 2.00(5) eV at ambient pressure to 1.56(5) eV at 16 GPa. First-principles simulations yield three infrared-active phonons, which soften with pressure, in contrast to the Raman-active phonons. These results agree with Raman spectroscopy experiments on FeWO and are similar to those previously reported for MgWO. Our results on FeWO are also compared to previous results on other wolframite-type compounds.