Alloying behavior of the rare earth metals with gold: the Ho–Au, Er–Au and Tm–Au systems

Abstract

Phase relationships have been established for the Ho–Au, Er–Au and Tm–Au systems by means of the experimental investigation of a number of selected compositions using X-ray powder diffraction (XRD), optical (LOM) and scanning electron microscopy (SEM), electron probe microanalysis (EMPA) and differential thermal analysis (DTA). The Ho–Au system is characterized by eight intermediate phases: Ho 2Au (incongruent melting at 1095 °C), HoAu (congruent melting at ≈1700 °C), Ho 7Au 10 (incongruent melting at 1360 °C), HoAu 2 (congruent melting at 1350 °C), HoAu 3 (congruent melting at 1250 °C), Ho 14Au 51 (incongruent melting at 1060 °C), HoAu 4 (incongruent melting at 950 °C) and HoAu 6 (incongruent melting at 840 °C). The Er–Au and Tm–Au systems present six iso-stoichiometric phases. For the Er–Au system they are: Er 2Au (incongruent melting at 1120 °C), ErAu (congruent melting at 1710 °C), Er 7Au 10 (incongruent melting at 1350 °C), ErAu 2 (congruent melting at 1385 °C), ErAu 3 (congruent melting at 1285 °C) and ErAu 4 (incongruent melting at 1000 °C). For the Tm–Au system the phases are: Tm 2Au (incongruent melting at 1160 °C), TmAu (congruent melting at 1720 °C), Tm 7Au 10 (incongruent melting at 1345 °C), TmAu 2 (congruent melting at 1430 °C), TmAu 3 (congruent melting at 1300 °C) and TmAu 4 (incongruent melting at 1035 °C). Crystal structure data and lattice parameters are given.