A contribution to the rare earth intermetallic chemistry: Praseodymium-magnesium alloy system

Pr-Mg alloys were studied in the range 0–100 at. % Mg. By using X-ray powder diffraction, optical and scanning electron microscopy, electron probe micro-analysis and differential thermal analysis, the different intermediate phases were identified and their crystal structures confirmed or determined. The following phase equilibria have been also determined: PrMg (cubic, cP2, CsCl type, melting point 765°C), PrMg₂ (cubic, cF24, MgCu₂ type, peritectic formation 740°C), PrMg₃ (cubic, CF16-BiF₃ type, melting point 790°C), Pr₅Mg₄₁ (tetragonal, tI92 Ce₅Mg₄₁-type, peritectic formation 575°C) and PrMg₁₂ (tetragonal, tI26 ThMn₁₂-type, peritectic formation 565°C) PrMg₂ undergoes a eutectoidal decomposition at 670°C. Three eutectic reactions were observed to occur at 735°C and 40·0 at. % Mg, at 725°C and 59·5 at. % Mg and at 560°C and 95·0 at. % Mg, respectively. The (β-Pr) terminal solid solution was observed to decompose eutectoidally at 510°C and 19·5 at. % Mg. The data obtained in this study are compared with those relating to other previously studied R-Mg systems.The crystallochemical characteristics of the binary phases formed by Mg with the rare earths and with the alkaline earths are briefly discussed.