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The intermetallic compounds of rare earths with RAg 0.5 Ga 1.5 composition (R=Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Lu and Y) have been studied. Their crystal structures have been found to be related to the hP6–CaIn 2 type. The stability range of this structure, which often occurs when the valence electron concentration is near to 8/3, has been analysed for the Gd–Ag–Ga alloys. The study of the GdAg 2 –GdGa 2 section has revealed that with increasing GdGa 2 -content the following sequence of structure types occur: oI 12-CeCu 2 , hP 6-CaIn 2 , hP 3-CeCd 2 , hP 3-AlB 2 . The YbAg 2 –YbGa 2 section has also been partially analysed.

The alloying behavior of the different rare earths, which varies according to systematic patterns, can be used to predict constitutional properties of rare earth alloys with the same element. The applicability to prediction of the TmMg phase diagram is presented here. The predicted version is compared with that determined experimentally by analyzing a few key compositions using X-ray powder diffraction, optical and scanning electron microscopy, electron probe microanalysis (EPMA) and differential thermal analysis (DTA). The following phases were identified and their crystal structures confirmed or determined: β phase, ≈Tm 2 Mg (cubic, cI 2, W type), TmMg (cubic, cP 2, CsCl type), TmMg 2 (hexagonal, hP 12, MgZn 2 type) and ≈Tm 5 Mg 24 (cubic, cI 58, α-Mn type). All the phases show peritectic formation. Two other equilibria were also observed: a eutectic reaction at 575 °C and 89 at.% Mg and the eutectoid decomposition of the β phase at 670 °C and approximately 30 at.% Mg.

The NdSn phase diagram was studied in the 55–80 at.% Sn composition range by differential thermal analysis, X-ray powder diffraction, optical and scanning electron microscopy and electron probe microanalysis. Five intermediate phases were identified in this range and their melting behavior was determined: NdSn3 (cubic, cP4AuCu3, m.p. 1150°C), Nd2Sn5 (orthorhombic, oC28Ce2Sn5, peritectic decomposition 1135 °C), Nd3Sn7 (orthorhombic, oC20Ce3Sn7, per.dec.1145 °C), NdSn2 (oC12NdSn2, m.p.1180 °C) and Nd3Sn5 (per.dec.1140 °C). Two eutectic equilibria were found at 1130 °C and 60.5 at.% Sn and 1130 °C and 73 at.% Sn.