Ternary Germanides RE_2Ge_2Mg (RE = Y,La-Nd,Sm,Gd,Tb)

摘要

The ternary rare earth metal-magnesium-germanides RE_2Ge_2Mg (RE = Y,La-Nd,Sm,Gd,Tb) were synthesized by reaction of the elements in sealed tantalum tubes in a water-cooled sample chamber of an induction furnace.The germanides were characterized through their X-ray powder patterns.The structures of Ce_2Ge_2Mg and Pr_2Ge_2Mg were refined from X-ray single crystal diffrac-tometer data:Mo_2FeB_2 type,P4/mbm,a = 750.6(1),c = 442.4(1) pm,wR2 = 0.0378,386 F~2 values,12 variable parameters for Ce_2Ge_2Mg,and a = 745.7(1),c = 439.2(l)pm,wR2 = 0.0462,448 F values,12 variable parameters for Pr_2Ge_2Mg.The lanthanum compound shows a homogeneity range La_(2+X)Ge_2Mg_(1-x).The structure of a single crystal with x = 0.249(5) was refined from X-ray data:a = 770.52(7),c = 447.4(1) pm,wR2 = 0.0481,322 F~2 values,13 variable parameters.The RE_2Ge_2Mg structures can be considered as a 1:1 intergrowth of CsCl and A1B_2 related slabs of compositions REMg and REGe_2.