2017/08/02 by Lisa Siggelkow, Viktor Hlukhyy, Thomas F. Fässler
paper · doi:10.1002/zaac.201700180
The influence of the partial substitution of Ni atoms by the similarly sized but electron‐richer Ge atoms with a similar electronegativity in the binary Laves phase MgNi 2 is investigated. A small degree of substitution in MgNi 2– x Ge x ( x = 0.1) leads to the change of the hexagonal MgNi 2 ‐type structure (C36) to the cubic C15 type, whereas higher amounts of Ge lead to the formation of the two new Laves phases Mg 2 Ni 3 Ge and MgNi 1.30(5) Ge 0.70 , which were synthesized by the direct reaction of the elements in alumina and niobium crucibles using an induction furnace. The crystal structures of the two phases were determined by single‐crystal X‐ray diffraction. Mg 2 Ni 3 Ge ( hR 18‐MgNi 2– x Ge x , x = 0.5) crystallizes in the Y 2 Rh 3 Ge‐type structure, which is an ordered variant of the cubic Laves phase MgCu 2 : space group R 3 m, a = 5.0300(7), c = 11.330(2) Å. hP 36‐MgNi 2– x Ge x with x = 0.70(6) crystallizes as a superstructure of the hexagonal Laves phase MgZn 2 : space group P 6 3 / mcm, a = 8.6946(2), c = 7.8127(3) Å. MgNi 1.3 Ge 0.7 represents a new structure type. Gradual substitution of Ni by Ge in the Laves phase MgNi 2 corresponds to an increase in the valence electron concentration (VEC) in the ternary phase system and leads to the series MgCu 2 (C15 type), hR 18‐Mg 2 Ni 3 Ge (superstructure of MgCu 2 type), and hP 36‐MgNi 1.3 Ge 0.7 (superstructure of MgZn 2 type). The electronic structures are discussed based on band structure calculations, and the results are compared to the pristine Laves phase MgNi 2 , MgCu 2 , and MgZn 2 with VEC = 2/3, 4/3 and 2, respectively.