On the compression mechanism of FeF3

Abstract

The structure of FeF₃, iron trifluoride, has been studied in the pressure range from ambient to 8.28 GPa by time-of-flight neutron powder diffraction. No structural phase transitions were found within the investigated pressure range, and least-squares refinements of the crystal structures were performed in the space group R\overline 3 c for all recorded data sets. It was found that volume reduction is achieved through rotation of the FeF₆ octahedra, and the Fe—F—Fe bond angle decreases from 152.5 (2) to 134.8 (3)° within the investigated pressure range. A small octahedral strain was found to develop during compression, which reflects an elongation of the FeF₆ octahedra along the c axis. The zero-pressure bulk modulus B_o and its pressure derivative B_o' were determined to be 14 (1) GPa and 12 (1), respectively.