Temperature-dependent structural studies of mullite-type Bi2Fe4O9

We report on the temperature-dependent structural studies on the mullite-type Bi2Fe4O9 compound. The crystal structures were determined using both powder X-ray diffraction and single crystal neutron diffraction. The thermal expansion of the cell parameters from smallest to largest occurred in the order a

Temperature-dependent stereochemical activity (eccentricity |Φi|) of the Bi3+ 6s2 lone electron pair directing in the non-bonded region of the Bi–O coordination in the Bi2Fe4O9 iron framework (given as polyhedra).Figure optionsDownload as PowerPoint slideHighlights
► Complex expansion–contraction mechanism explains anisotropic thermal expansion.
► Bi 6s2 lone electron pair sphericity influences analyses by FTIR autocorrelation.
► Intrinsic effects at 773 K are responsible for extrinsic parameter changes at 900 K.