The Influence of the Valence Electron Concentration on the Structural Variation of the Laves Phases MgNi_2–xGe_x

Abstract

Abstract. 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 (hR18-MgNi 2-x Ge x , x = 0.5) crystallizes in the Y 2 Rh 3 Ge-type structure, which

Rhombohedral Distortion of the Cubic MgCu2-Type Structure in Ca2Pt3Ga and Ca2Pd3Ga

“…Ca2M3Ga (M = Pt, Pd) crystallize in the Y2Rh3Ge structure type [29], which is a rhombohedral distortion of the cubic Laves phase MgCu2-type structure, as discussed by Doverbratt et al [3] and Siggelkow et al [2]. The M atoms occupy 9e Wyckoff positions which buildup 3.6.3.6 Kagomé nets orthogonal to the c-axis [2]. The Ga atoms cap alternate triangular faces of the…”

“…The first ordered ternary Laves phase with the direct rhombohedral distortion of the MgCu 2 -type, first evidenced in the binary TbFe 2 phase, which distorts via magnetostriction, was reported to be Mg 2 Ni 3 Si [11,12]. Recently, many examples of this rhombohedral distortion, with varying vec, have been reported: RE 2 Rh 3 Si (RE = Pr, Er), U 2 Ru 3 Si, Ce 2 Rh 3+x Si 1−x , RE 2 Rh 3 Ge, Ca 2 Pd 3 Ge, Sm 2 Rh 3 Ge, U 2 Ru 3 Ge, Mg 2 Ni 3 Ge [2], Mg 2 Ni 3 P, and the heretofore only known gallides RE 2 Rh 3 Ga (RE = Y, La-Nd, Sm, Gd-Er).…”

“…The maximal translationengleiche subgroup of the Fd-3m space group that allows for the ordered 3:1 ratio of M:Ga atoms is R-3m [2,3,11]. Reported herein is the first extensive computational study of the "coloring problem" [13] for this rhombohedral distortion of the cubic cell.…”

“…Laves phases are the largest class of intermetallic compounds with the general formula AB 2 . Binary Laves phases primarily crystalize in one of three crystal structures: MgCu 2 , MgZn 2 , or MgNi 2 [2]. These structure types, which appear in a vast number of intermetallic systems, contain topologically closed-packed Frank-Kasper polyhedra and have been intensely studied for magnetic and magnetocaloric properties, hydrogen storage, and catalytic behavior [3][4][5][6][7][8][9].…”

Ternary Laves phases Sc0.22(1)Ta0.78(1)Fe2 and Sc0.63(1)In0.37(1)Co2 – coloring variants of the MgZn2 and MgNi2 type

“…The different phases can be grouped through the percentage of the hexagonal stacking and this correlates with the VEC. These crystal chemical principles along with considerations of the bonding peculiarities are summarized in different original articles and reviews [11–28] …”