On the compression mechanism of FeF3

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 leastsquares refinements of the crystal structures were performed in the space group R3c 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)degrees 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.