Distribution of Mn3+ and Mn4+ species between octahedral and square pyramidal sites in Bi2Mn4O10-type structure

The cationic distribution in the iron substituted manganites Bi2Mn4-xFexO10 (0 less than or equal to x less than or equal to 1) has been investigated combining X-ray powder diffraction (XRPD), magnetic susceptibility measurements and Fe-57 Mossbauer spectroscopy. Iron is at the trivalent state and exhibits, like Mn3+ the high spin configuration. It is shown that Fe3+ is distributed over the two sites of the structure, octahedral and square pyramidal, with a preferential occupation of the second one. Consideration of the Mn(Fe)-O distances leads, for x = 1, to the cationic distribution Bi-2[Mn1.664+Fe0.343+](O)[Mn1003+Mn0.344+Fe0.663+](P) O-10, showing that Mn4+ is also susceptible to sit in the pyramidal site. Magnetic and structural study of the oxides Bi2Mn4-xTixO10 (0 less than or equal to x less than or equal to 1) and Bi2Mn3.75Al0.25O10 suggests that Ti4+ and Al3+ respectively sit in the octahedral and square pyramidal sites of the structure according to the formulae Bi-2[Mn2-x4+Tix4+](O)[Mn-2(3+)](P) O-10 and Bi-2[Mn-2(4+)](O)[Mn1.753+Al0.253+](P) O-10.