Structure of amorphous ferrites of lanthanum, dysprosium, and bismuth

Mechanical activation of the lanthanum, dysprosium, and bismuth morphotropic series of ferrites with perovskite structure leads to the formation of amorphous materials. Mössbauer spectra indicate lowering of the Fe³⁺ coordination number on amorphization. X-ray diffraction reveals the changes in the short-range order of the arrangement of the heavy cations with respect to the starting crystalline samples, as well as structural differences between the amorphous ferrites. The structure of the amorphous LaFeO₃ can be described as quasicrystalline with trigonal-prismatic La³⁺ configuration. Structural differences between the amorphous samples are due to distortions in the perovskite cells of the original crystal namely: an ionic misfit in DyFeO₃, and covalency of the chemical bonds in BiFeO₃.