A high-pressure study of epsilon-FeSi, between 0 and 8.5 GPa, by time-of-flight neutron powder diffraction

The crystal structure of cubic iron monosilicide, epsilon-FeSi, has been determined at six pressures between 0 and 8.5 GPa by time-of-flight neutron powder diffraction, using the POLARIS diffractometer at the ISIS spallation neutron source. At all pressures, the material has space group P2(1)3, with Z = 4 and both atoms on sites 4(a) (x, x, x). The unusual sevenfold coordination of both atoms is unaltered by pressure, with the atomic coordinates remaining essentially fixed at x(Fe) = 0.137 (1) and x(Si) = -0.157 (1) throughout. An almost uniform compression of up to approximately 2% in interatomic distances is observed, owing to the reduction in cell parameter.