Structur–Composition Relations and Fractional Site Occupancy of New M5Ge4 Compounds in the System Ge–Ta–Zr

New Ternary Compounds MxTa11−xGe8 (M=Ti, Zr, Hf): Structure and Stabilization

“…Due to the similar properties of these metals one might assume that extended solid solutions rather than new ternary compounds will be formed as the main result of the addition of a third transition metal element to a binary M-Ge system. This point of view, however, was not confirmed by our recent study in the Ge-Zr-Ta system, where we could find the two new ternary compounds Zr 4Àx Ta 1+x Ge 4 and Zr 2+x Ta 3Àx Ge 4 , showing fractional site occupancy between Ta and Zr at the metal sites in combination with strong site preferences on different sites (1). Similar structural features (i.e., the variation of the metal-to-metal ratio at different mixed metal sites) have been observed earlier for several ternary sulfides and phosphides like, e.g., mixed Nb-Ta sulfides (2-5), Hf 10 Ta 3 S 3 (6) and Hf 5.08 Mo 0.92 P 3 (7).…”

“…Zirconium shows clear preference for only three of the nine independent metal sites (M1, M2 and M4). Zr x Ta 11Àx Ge 8 thus shows DFSO-like behavior similar to the compounds Zr 4Àx Ta 1+x Ge 4 and Zr 2+x Ta 3Àx Ge 4 reported previously (1). In contrast, the compound Ti x Ta 11Àx Ge 8 does not exhibit pronounced site preferences among different independent sites and Ti was found to be distributed over the different metal sites in a rather uniform way.…”

Site Preference of Metal Atoms in Gd5–xMxTt4 (M = Zr, Hf; Tt = Si, Ge)

“…Another interesting observation derived from the data in Table 4 is that the site preferences do not depend on the VEC. For the non‐isoelectronic substitution in the R 5– x Ca x Ge 4 ( R = La, Ce),13 R 5– x Mg x Ge 4 ( R = Gd–Lu, Y), Zr 5– x Ta x Ge 4 and Hf 5– x Nb x Ge 4 systems,29,32,33 all guest atoms show preference for the M 3 site regardless whether the total VEC increases or decreases. However, the sequence of metal‐site occupation in these three systems is adjusted to the order of M 3 > M 2 > M 1.…”

On the Crystal Structure, Metal Atom Site Preferences and Magnetic Properties of Nd5–xErxTt4 (Tt = Si or Ge)

“…In the Nd/Er/Si system we observe a structural transition from the tetragonal Zr 5 Si 4 -type [18] crystal structure (which is a typical structure type for the silicon-rich, lighter rareearth cases) to the orthorhombic Gd 5 Si 4 -type [19] structure (which is a typical structure type for the silicon-rich, heavier rare-earth cases). For the Nd/Er/Ge system, together with variations in magnetic ordering, we also observe a structural transformation from the orthorhombic Sm 5 Ge 4 -type [20] to a new monoclinic U 2 Mo 3 Si 4 -type [21] structure for certain compositions. This structure is different from the known monoclinic structure of Gd 5 Si 2 Ge 2 -type [6] and, until recently, was not reported for other RE 5 T 4 systems [15].…”