Crystal structure refinement of the mechanically activated spinel-ferrite

The crystal structure of the mechanically activated (ball milled) zinc ferrite has been studied using Xray powder diffraction and Mossbauer spectroscopy. On the basis of the Rietveld analysis the exact coordinates of atoms, the unit cell dimension, the oxygen parameter, the atom occupation factors as well as the interatomic distances in mechanically activated zinc ferrite have been determined. It was found that mechanical activation of zinc ferrite results in the decrease of the occupation factor of both zinc and iron cations in tetrahedral (A) and octahedral [B] positions, respectively, (i.e. mechanically induced inversion takes place) as well as in the decrease of both unit cell dimension and oxygen parameter. In the process of mechanical activation the translation invariance of the zinc ferrite structure is preserved. In addition to a small change in the lengths of tetrahedral and octahedral bonds, the contraction of the crystal lattice is accompanied mainly by the deformation of octahedron: the shared octahedral edges become longer than the unshared ones. Since the distances tetra-tetra, octa-tetra and octa/cation-octa/cation do not change significantly, the change in the octahedron geometry results in the alteration of the octa/cation-anion-octa/cation bond angle. It was found that mechanically induced changes in magnetic properties of zinc ferrite are caused by the onset of the intersublattice exchange interaction of the Fe3+(A)-O2--Fe3+[B] type (with bond angle of 125 degrees), taking place due to the mechanically induced inversion as well as by the onset of the intrasublattice exchange interaction of the Fe3+[B]-O2--Fe3+[B] type with deformed bond angles different from 90 degrees.