Compositions of phases in the interaction of rare-earth metals with selenium

The interaction of rare-earth metals (Pr, Nd, Sm, Y, Er, and Yb) with selenium at Ln: Se = 1: 2, 2: 3, 3: 4, and 1: 1 under polythermal (293–1270 K) and isothermal (770 and 1170 K) heat treatment conditions was studied by differential thermal and X-ray powder diffraction analyses. While heating the reaction mixture, the exothermic events in the interaction between elements occur within the temperature ranges 620–750 K (Pr), 580–870 K (Sm), and 620–920 K (Er). X-ray powder diffraction analysis detected the formation of the following phases in the homogeneous state: at 770 K, LnSe₂ and Yb₂Se₃, and at 1170 K, Ln₃Se₄, Ln₂Se₃, and YbSe. Scanning electron microscopy showed that particles of the selenide phases are formed by 1 × 2–5-μm fragments, which constitute a spongy structure of agglomerates tens to hundreds of micrometers in size.