Mössbauer study of the local environment and chemical state of tin atoms applied by impregnation on an MnTiO3 substrate

Tin(IV) ions introduced into the surface of MnTiO3 crystallites upon annealing in argon occupy positions with nonequivalent cationic environments and are characterized by different magnetic hyperfine fields H. The chemical behavior of these dopant ions depends on their local cationic environment. Upon annealing in hydrogen at 673 K, approximately half of the Sn(IV) ions retain their valence state. This annealing leads to the formation of comparable amounts of tin as clusters of the beta-Sn type and as doubly charged cations. The Sn-119(II) spectral parameters (at 5 K, the isomer shift is delta = 2.91 +/- 0.02 mm/s, the quadrupole splitting A = 2.20 +/- 0.04 mm/s) indicate that these cations exist as isolated dopant centers at the surface faces of MnTiO3. The anionic environment of these ions differs only slightly from that they have at the surface of Cr2O3 crystallites. However, despite the fact that MnTiO3, Similarly to Cr2O3, contains magnetically active cations, the Sn-119(II) ions in it are not subjected to spin polarization (at 5 K, the hyperfine field H = 0 kOe). The lack of polarization is explained by the fact that Sn(II) ions preferentially occupy those positions in which they are surrounded by diamagnetic Ti(IV) cations, which tend, to a greater extent than Mn(II), to retain their octahedral coordination by oxygen anions.