Direct observation of structural changes near and at the charge-ordering temperature of ilvaite using high-flux neutron powder diffraction

Abstract

The detailed structural changes that occur during and following the formation of a long-range, charge-ordered state have been accurately and rapidly determined. The localisation of the electron in ilvaite, Ca(Fe,Mn)₃Si₂O₈(OH), forming Fe²⁺ and Fe³⁺ from the delocalized 2× Fe^2.5+, is directly apparent in bond valence sums derived from accurately determined Fe–O distances extracted from neutron powder diffraction data obtained for 40 temperatures around the charge ordering temperature in just a few hours. Subtle changes that occur in the structure and lattice parameters after the formation of the charge-ordered state are also apparent for the first time from this work.