Variable temperature powder neutron diffraction study of the Verwey transition in magnetite Fe3O4

Neutron powder diffraction data have been collected from a sample of polycrystalline Fe3O4. High resolution data collected at 60 K are fitted using a simple rhombohedral distortion of the cubic unit cell. This model accounts for all of the peak splittings that occur upon cooling through the Verwey transition temperature (T-V). Lower resolution data collected between 2 and 280 K are fitted using the same model, which gives T-V= 110 +/- 5 K. These data show a change in the thermal expansion due to the softening of phonons above T-V and a change in crystallite extinction arising from twinning at the transition. (C) 2000 Editions scientifiques et medicales Elsevier SAS. All rights reserved.