Electronic, Vibrational, and Structural Properties of the Natural Mineral Ferberite (FeWO 4 ): A High-Pressure Study.

This paper reports an experimental high-pressure study of natural mineral ferberite (FeWO 4 ) 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 4 crystallizes in the wolframite structure at ambient pressure and is stable over a wide pressure range, as is the case for other wolframite AWO 4 (A = Mg, Mn, Co, Ni, Zn, or Cd) compounds. No structural phase transitions were observed for FeWO 4 , in the pressure range investigated. The bulk modulus ( B 0 = 136(3) GPa) obtained from the equation of state is very close to the recently reported value for CoWO 4 (131(3) GPa). According to our optical absorption measurements, FeWO 4 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 4 and are similar to those previously reported for MgWO 4 . Our results on FeWO 4 are also compared to previous results on other wolframite-type compounds.