Study of Iron Impurity in Silver Chloride Using Mainly the Mössbauer Effect

The Mössbauer effect has been investigated as a function of temperature between 4 and 550°K for sources of ${\mathrm{Co}}^{57}$ impurity diffused into single-crystal silver chloride. Auxiliary measurements of ionic conductivity, optical absorption, ESR, and dielectric dispersion have also been made. The Mössbauer spectrum of a freshly prepared sample is attributed to a ferrous ion in a substitutional site bound to a positive ion vacancy in a unique (100) position. Between 4 and 230°K a simple quadrupole doublet is observed which is interpreted to show a measure of covalency in the ferrous ion. Above 230°K the spectral lines broaden and the spectrum collapses to a single line; it is proposed that this effect is a result of the thermal motion of the vacancy around the impurity. The deduced vacancy jump times are shown to agree with those derived from dielectric-dispersion measurements. Aged samples have complex Mössbauer spectra which are explained by the formation of additional centers of ferrous ions bound to anion impurities.