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

The temperature dependence of the 197Au, 166Er, and 169Tm Moessbauer effect was studied in intermediate phases of RAu (R = Sc, Ho, Er, Tm, Yb, Lu) with the CsCl structure. 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 4.20K for various compounds is obtained. Moessbauer-absorption patterns for 166Er in ErAu have a temperature dependence which is characteristic of relaxation effects. Isomer-shift systematics for 197Au in RAu for the CsCl and the transformed close-packed phases are discussed. (auth)