Mössbauer Spectroscopy in Group-III Antimonides

Abstract

M\"ossbauer absorption spectra of the group-III antimonides AlSb, GaSb, and InSb, and ternary alloys of the latter two compounds have been taken at 78 \ifmmode^\circ\else\textdegree\fi{}K, using the 37.2-keV, ${\frac{7}{2}}^{+}\ensuremath{\rightarrow}{\frac{5}{2}}^{+}$ transition in ${\mathrm{Sb}}^{121}$. An absorber of KSb${\mathrm{F}}_{6}$ was used to help determine the nuclear factor $\frac{\ensuremath{\delta}R}{R}=(\ensuremath{-}6.7\ifmmode\pm\else\textpm\fi{}3)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$. Chemical bonding in these compounds has both ionic and covalent character raising the question of relative ionicity. Molecular-orbital (MO) and linear-combination-of-atomic-orbital calculations, together with an assessment of electronegativity differences, predict that ionicity increases for the series GaSb, InSb, and AlSb, whereas measurements of the M\"ossbauer isomer shift along with some bulk and atomic properties show that ionicity increases in the series InSb, GaSb, and AlSb. Interpretation of the isomer-shift data is somewhat complicated by shielding of the $p$ electrons at the Sb nucleus, but electron populations determined by MO calculations indicate that the $5s$-electron population is nearly the same on the Sb nuclei in the three compounds, in accord with the results of Hafemeister et al. on alkali iodides and those of Lees and Flinn on tin compounds. Thus, the $5s$-electron population tends to be constant in compounds of these three elements from the same row of the periodic chart. Though the single-line M\"ossbauer absorption spectra were broad for some absorbers, there was no evidence of quadrupole hyperfine structure which would have been apparent from asymmetry of the absorption lines.