Mykhalichko O. Phase equilibria and crystal structures of compounds in the {La, Gd, Er}-Cu-Ga-Si systems at 600°C

The phase equilibria at 600°С in the ternary {La, Gd, Er}-Cu-Ga systems in the whole concentration range, and in the quaternary {La, Gd, Er}-Cu-Ga-Si systems at 20 and 33.3 at.% R (rare-earth metal), were investigated using X-ray diffraction and, in part, microstructure, energy-dispersive X-ray and differential thermal analyses. Isothermal sections of the phase diagrams of the {La, Gd, Er}-Cu-Ga and {La, Gd, Er}-Cu-Ga-Si systems (at 33.3 at.% R) were constructed. The boundaries of the solid solutions based on the binary and ternary compounds were determined. The existence of 21 ternary compounds was confirmed and 22 new ternary gallides were discovered in the above-mentioned and related systems. The crystal structures of 32 compounds were completely determined. The existence of six continuous solid solutions with the structure types AlB2 and a-ThSi2, and five limited substitutional solid solutions, was established in the quaternary systems. In total, complete structural refinements were carried out from 142 powder and 8 single crystal X-ray diffraction patterns. Four new structure types, GdCu2.95Ga1.05, Er14Cu47.04Ga3.96, TmCu8Ga4 and Tm14Cu46Ga5, were discovered. The main features of the formation of intermetallic phases in the {La, Gd, Er}-Сu-Gа and {La, Gd, Er}-Сu-Gа-Si systems and the influence of electronic factors on their crystal structure were studied. For the compounds with high Ga (Ga and Si) content, statistical mixtures of small-size atoms were found, whereas for the compounds with high Cu content, a tendency towards atom ordering with the formation of [Cun] clusters was observed.