Low-temperature phase transition and isomer-shift systematics in intermediate phases of rare-earth—gold compounds

Abstract

The temperature dependence of the ${}_{}{}^{197}{}_{}{}^{}\mathrm{Au}$, ${}_{}{}^{166}{}_{}{}^{}\mathrm{Er}$, and ${}_{}{}^{169}{}_{}{}^{}\mathrm{Tm}$ Mössbauer effect has been studied in intermediate phases of $R\mathrm{Au} (R=\mathrm{S}\mathrm{c},\mathrm{H}\mathrm{o},\mathrm{E}\mathrm{r},\mathrm{T}\mathrm{m},\mathrm{Y}\mathrm{b},\mathrm{L}\mathrm{u})$ with the CsCl structure. Our results indicate that the CsCl structure is metastable and undergoes a low-temperature martensitic phase transformation to a close-packed (FeB-like) structure. The ratio of the quantity of the two phases present at 4.2°K for various compounds is obtained. Mössbauer-absorption patterns for ${}_{}{}^{166}{}_{}{}^{}\mathrm{Er}$ in ErAu have a temperature dependence which is characteristic of relaxation effects. Isomer-shift systematics for ${}_{}{}^{197}{}_{}{}^{}\mathrm{Au}$ in $R\mathrm{Au}$ for the CsCl and the transformed close-packed phases are discussed.