Dynamics of Phase Transitions and Polymorphism Suppression in the LaMn1-xFexO3+d Compound (x = 0.015-0.5)

The effect of a Fe concentration on the dynamics of the phase transitions and on the suppression of the polymorphism in LaMn1-xFexO3+d(x = 0.015-0.5) has been investigated by Mossbauer spectroscopy and X-ray diffraction analysis. At a small Fe concentration (x < 10%), two orthorhombic phases Pnma I and Pnma II (total space group Pnma) and rhombohedral phase (space group R-3c) are formed in Fe-doped LaMnO3+d depending on the synthesis conditions and heat treatment. When the Fe concentration reaches 10%, the Pnma II phase disappears. The rhombohedral phase begins to be suppressed when the Fe concentration is further increased and disappears when the Fe concentration reaches the level of 50%. Only single orthorhombic phase Pnma I remains which keeps its structure stability under any heat treatment. Based on the obtained experimental data, the dynamics of the phase transitions and polymorphism suppression in the LaMn1-xFexO3+d compound have been analyzed with an increase in the Fe concentration. It has been shown that the mechanisms of phase suppression are different for Pnma II and R-3c phases.