Phase equilibria in the GdAu system

Abstract

Abstract The GdAu phase diagram was studied in the 0–100 at% Au composition range by differential thermal analysis (DTA), X-ray diffraction (XRD), optical and scanning electron microscopy (SEM) and electron probe microanalysis (EPMA). Eight intermetallic compounds were identified and their melting behaviour was determined: Gd 2 Au (orthorhombic, oP12-Co 2 Si type, peritectic decomposition 935 °C), GdAu (L.T. form, orthorhombic, oC8-CrB type, and H.T. form, cubic, cP2-CsCl type, m.p. 1585 °C), Gd 3 Au 4 (trigonal, hR42-Pu 3 Pd 4 type, peritectic decomposition 1340 °C), Gd 7 Au 10 (tI136-Gd 7 Au 10 , peritectic decomposition 1160 °C), GdAu 2 (tetragonal, tI6-MoSi 2 type, m.p. 1180 °C), GdAu 3 (orthorhombic, oP8-TiCu 3 type, m.p. 1200 °C), Gd 14 Au 51 (hexagonal, hP65-Gd 14 Ag 51 type m.p. 1165 °C) and GdAu 6 (tetragonal, tP56-SmAu 6 type, peritectic decomposition 855 °C). Five eutectic reactions were observed to occur at 845 °C and 21.0 at% Au, at 1140 °C and 63.5 at% Au, at 1110 °C and 70.5 at% Au, at 1135 °C and 77.0 at% Au and at 800 °C and 89.0 at% Au, respectively. A catatectic decomposition reaction of the (β-Gd) phase was also found at 1220 °C and ≈ 3 at% Au. The crystal structures of the Gd 3 Au 4 and Gd 7 Au 10 phases were determined by single crystal methods. Gd 3 Au 4 is isotypic with Pu 3 Pd 4 . The Gd 7 Au 10 phase is of a new type and can be described as a sequence of layers perpendicular to the c -axis in which three kinds of layers are recognizable. The results are briefly discussed and compared with those of the SmAu system.