Mössbauer studies of mixed-valence manganite Pb3(Mn0.965Fe0.035)7O15

Pb3Mn7O15 manganite with mixed valence (Mn3+/Mn4+) was studied by Mössbauer effect on 57Fe impurity atoms in the temperature range of 80–673 K. The experimental spectra consisted of two main quadrupole doublets corresponding to trivalent Fe atoms replacing Mn atoms in different positions in the crystal lattice. Identification of the doublets was made on the basis of calculations of quadrupole splitting within the point charges model and taking possible polarization of oxygen ions into account. In two temperature ranges: T ≈ 370–510 K, corresponding to the structural phase transition, and at T ≈ 140–230 K, where strong anomalies of the magnetic and electrical properties were observed, the sharp changes in the hyperfine quadrupole splitting were observed. It is assumed that these changes are caused by changes in the valence of manganese ions and structural deformations.