Mössbauer-spectroscopic Characterization of the Local Surrounding of Tin Dopant Cations in the Bulk and on the Surface of YCrO₃ Crystallites

Abstract

119 Sn Mössbauer spectra of tin-doped YCrO 3 , obtained by annealing in air of an YCr( 119 Sn 4+ ) 0.003 (OH) 6 ·xH 2 O precursor, provide evidence for the location of Sn 4+ on the Cr 3+ site in the bulk of crystallites. Below the Néel point of YCrO 3 (T N = 141 K), Sn 4+ ions are spinpolarized, the majority exhibiting a hyperfine field H of 80 kOe at 4.2 K. Analysis of the 119 Sn spectra of another sample, obtained by impregnation of polycrystalline YCrO 3 with a solution of 119 SnCl 4 , shows that annealing in H 2 results in the location of the dopant, in the divalent state, on the surface of the crystallites. The parameters of an in situ 119 Sn spectrum at 295 K (isomer shift δ = 2.76 mm s −1 and quadrupole splitting E Q = 1.95 mm s −1 ) reveal the presence of Sn 2+ ions on sites with a coordination number CN < 6. At 100 K these Sn 2+ ions exhibit no spin polarization. Upon contact with air they are rapidly oxidized to the tetravalent state, as demonstrated by their modified isomer shift value δ = 0.06 mm s −1 . For the large majority of both the residual "parent" Sn 2+ ions and the "daughter" Sn 4+ 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 Y 3+ sites with an equal number of Cr 3+ neighbors having mutually opposite spin orientations.