The isothermal section of the La–Si–Mg system at 500 ∘C

The isothermal section of the La–Si–Mg system at 500 ∘C was constructed in the whole concentration range by means of the SEM-EDXS and XRPD characterization of about forty alloys prepared by induction melting and then annealed. Phase equilibria are characterized by the following ternary phases: τ1-La2+xSi2Mg1−x (0≤x≤0.35,tP10-Mo2FeB2), τ2-LaSi2Mg2 (tP5-CeSi2Mg2), τ3-LaSi2Mg (structure still unknown) and τ4-La6SiMg23 (cF120-Zr6SiZn23). The high temperature binary phase LaMg2 (cF24-MgCu2) has been found to be stabilized at 500 ∘C probably by a small amount of Si. Phases in binary subsystems do not generally form extended ternary solid solutions except for (La1−xMgx)3Si2 (0≤x≤0.167,tP10-U3Si2). Crystal structures of phases τ1-La2+xSi2Mg1−x and (La1−xMgx)3Si2 are correlated, the former being a substitution derivative of the latter.