The Influence of the Valence Electron Concentration on the Structural Variation of the Laves Phases MgNi2–xGex

Zeitschrift für Anorganische und Allgemeine Chemie

4 years ago

The Influence of the Valence Electron Concentration on the Structural Variation of the Laves Phases MgNi2–xGex

Lisa Siggelkow, Thomas F. Fässler, Viktor Hlukhyy

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 MgNi2 is investigated. A small degree of substitution in MgNi2–xGex (x = 0.1) leads to the change of the hexagonal MgNi2-type structure (C36) to the cubic C15 type, whereas higher amounts of Ge lead to the formation of the two new Laves phases Mg2Ni3Ge and MgNi1.30(5)Ge0.70, 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. Mg2Ni3Ge (hR18-MgNi2–xGex, x = 0.5) crystallizes in the Y2Rh3Ge-type structure, which is an ordered variant of the cubic Laves phase MgCu2: space group R3m, a = 5.0300(7), c = 11.330(2) Å. hP36-MgNi2–xGex with x = 0.70(6) crystallizes as a superstructure of the hexagonal Laves phase MgZn2: space group P63/mcm, a = 8.6946(2), c = 7.8127(3) Å. MgNi1.3Ge0.7 represents a new structure type. Gradual substitution of Ni by Ge in the Laves phase MgNi2 corresponds to an increase in the valence electron concentration (VEC) in the ternary phase system and leads to the series MgCu2 (C15 type), hR18-Mg2Ni3Ge (superstructure of MgCu2 type), and hP36-MgNi1.3Ge0.7 (superstructure of MgZn2 type). The electronic structures are discussed based on band structure calculations, and the results are compared to the pristine Laves phase MgNi2, MgCu2, and MgZn2 with VEC = 2/3, 4/3 and 2, respectively.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/zaac.201700180