Mössbauer-spectroscopic characterization of the local surrounding of tin dopant cations in the bulk and on the surface of YCrO3 crystallites
Résumé
119Sn Mössbauer spectra of tin-doped YCrO3, obtained by annealing in air of an YCr(119Sn4+)0.003(OH)6·xH2O precursor, provide evidence for the location of Sn4+on the Cr3+site in the bulk of crystallites. Below the Néel point of YCrO3 (TN= 141 K), Sn4+ions are spin-polarized, the majority exhibiting a hyperfine field H of 80 kOe at 4.2 K. Analysis of the119Snspectra of another sample, obtained by impregnation of polycrystalline YCrO3 with a solution of119SnCl4, shows that annealing in H2results in the location of the dopant, in the divalent state, on the surface of the crystallites. The parameters of an in situ119Sn spectrum at 295 K (isomer shiftδ=2.76mms−1and quadrupole splitting EQ=1.95mms−1) reveal the presence of Sn2+ions on sites with a coordination number CN<6. At 100 K these Sn2+ions exhibit no spin polarization. Upon contact with air they are rapidly oxidized to the tetravalent state, as demonstrated by their modified isomer shift valueδ=0.06mms−1. For the large majority of both the residual “parent” Sn2+ions and the “daughter” Sn4+ones no spin polarization is observed down to 4.2 K. This means that surface-located tin dopant cations, regardless of their oxidation state, occupy the Y3+sites with an equal number of Cr3+neighbors having mutually opposite spin orientations
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