Structure refinements of members in the brownmillerite solid solution series Ca2Alx(Fe0.5Mn0.5)2−xO5+δ with 1/2≤x≤4/3

Four different brownmillerite solid solutions Ca2Alx(Fe0.5Mn0.5)2−xO5+δ with 1/2≤x≤4/3 were synthesized by a solid oxide ceramic method. The phases crystallize either in a primitive centered orthorhombic cell with space group Pnma or in a body centered cell with space group I2mb dependent on the aluminum concentration present in the solid solution. Mn3+ ions occupy exclusively site 4a coordinated by six oxygen anions. Increasing Mn3+ concentrations cause a remarkable distortion of the octahedron and indirectly of the tetrahedron, resulting in twisted and tilted octahedral layers as well as buckled tetrahedral chains. The influences are discussed on the site 4a of trivalent manganese due to its Jahn-Teller activity, with regard to the occupation of octahedron and tetrahedron with different sized iron and aluminum ions.

Graphical AbstractThe coupled substitution Fe3+>Mn3++Fe3+ <=>2 Al3+ in brownmillerite phases (Ca2(Fe0.5Mn0.5)2−xAlxO5+δ) changes predominantly their structural properties, which is essential for the hydration performance of the calcium aluminate cement, where brownmillerites occur as clinker phases.Figure optionsDownload as PowerPoint slideHighlights
► We present structural data of four Ca-Al-Fe-Mn-brownmillerites.
► Mn3+-ions occupy exclusively the octahedrally coordinated site 0,0,0.
► Bonds and angles of the octahedrally coordinated site are distorted strongly.
► Mn3+-ions influence indirectly the shape of the tetrahedron.
► Mn3+-ions stabilize Pnma instead of I2mb in Ca-Al-Fe-Mn-brownmillerites.