Phase equilibria in the Pr-Tl system

The Pr-Tl system was studied in the composition range 15-100 at.% Tl using differential thermal analysis, metallography and X-ray examination. The praseodymium-rich alloys were reinvestigated and the published phase diagram was confirmed. The following intermetallic compounds were observed: Pr3Tl (decomposes at 800 ± 10 °C); Pr2Tl (decomposes at 940 ± 10 °C); Pr5Tl3 (decomposes at 1020 ± 10 °C); PrTl (melting point, 1260 ± 10 °C); Pr3Tl5 (melting point, 1120 ± 10 °C); PrTl3 (melting point, 1065 ± 10 °C). Four eutectics occur: β-Pr-Pr3Tl (767 ± 1 °C, 13.9 ± 0.1 at.% Tl); PrTl-Pr3Tl5 (1090 ± 10 °C, 58.0 ± 0.5 at.% Tl); Pr3Tl5-PrTl3 (1035 ± 10 °C, 69.0 ± 0.5 at.% Tl); PrTl3-β-Tl (303 °C, greater than 99.5 at.% Tl). β-Pr decomposes eutectoidally at 687 ± 1 °C and 8.0 ± 0.2 at.% Tl. The crystal structures of Pr3Tl (ordered-disordered cP4 AuCu3 and cF4 Cu types), Pr5Tl3 (tI32 W5Si3 type), PrTl (cP2 CsCl type) and PrTl3 (cP4 AuCu3 type) were confirmed. Pr3Tl5 was found to have an orthorhombic oC32 Pu3Pd5 type of structure. The characteristics of the phase diagram and the molar volumes of the Pr-Tl alloys are compared with those of the Ce-Tl and Nd-Tl systems. © 1981.