A Mössbauer study of rare-earth metal pyrochlores A2FeSbO7(A = Lu, Er, Tb, or Sm) using the 37.2-keV γ-ray of antimony-121

Abstract

Isomer shifts and quadrupole splittings have been obtained from the ¹²¹Sb Mössbauer spectra of four members of the pyrochlore series A₂FeSbO₇(A = Lu, Er, Tb, or Sm). The isomer shift (i.s.) decreases linearly with r(A³⁺), the radius of the rare-earth metal ion, and is in the opposite sense to that previously found for the ⁵⁷Fe i.s. in the same series. This result is interpreted in terms of a decrease in the covalent character of the Sb–O bonds as the distortion of the SbO₆ octahedron increases. The uadrupole-splitting results are of insufficient precision to show any clear trends.