Coloring, Distortions, and Puckering in Selected Intermetallic Structures from the Perspective of Group‐Subgroup Relations

Abstract

Group‐subgroup relations are a compact and concise tool for structure systemization. The present review summarizes the use of Bärnighausen trees for classification of intermetallic structures into structural families. The overview starts with group‐subgroup relationships between the structures of the metallic elements (W, In, α‐Po, β‐Po, Pa, α‐Sn, β‐Sn) followed by examples for ordered close‐packed arrangements that derive from fcc, hcp, and bcc subcells (e.g. CuAu, Cu3Au, MoNi4, ZrAl3, FeAl, MoSi2). The main focus lies on more complex structures that derive from aristotypes with comparatively high space group symmetry: AlB2, Fe2P, U3Si2, BaAl4, La3Al11, NaZn13, CaCu5, and Re3B. The symmetry reductions arise from coloring of sites with different atoms or from distortions / puckering due to size restrictions (different radii of atoms). The resulting superstructures are discussed along with the consequences for diffraction experiments, chemical bonding, and physical properties.

Crystal Structure, Spectroscopic Investigations, and Physical Properties of the Ternary Intermetallic REPt2Al3 (RE = Y, Dy–Tm) and RE2Pt3Al4 Representatives (RE = Tm, Lu)

“…Hence, they are shifted by 1/2 z compared to the original position. The same shift is also observed in YNi 2 Al 3 [16,35] and i7-PrNi 2 Al 3 [17]. Refinement as orthorhombic trilling, as suggested by the translationengleiche symmetry reduction of index 3, is not necessary because the orthorhombic crystal system was found directly by the indexing routine.…”

“…They exhibit 18-fold coordination environments in the shape of six-fold-capped hexagonal prisms (Figure 4 A view of the unit cell along the c axis readily reminds us of the ternary CaCu 5 [14], and the recently found i7 superstructure of PrNi 2 Al 3 [17]. Recoloring in intermetallics is found quite frequently, often accompanied by distortions and puckering within the respective structures [35]. These structural effects between different structure types can be investigated by so-called group-subgroup relations.…”

YPd2Al and YPd2Zn with LiCu2Sn Type Structure

“…The 2c, 4f, and 2a sites [2] show different coloring. [39,40] The compounds show a range for the valence electron count from 25 to 29. This offers distinct variations in the physical properties; however, only few of these materials have been studied in detail.…”

Quaternary Germanides RE3TRh4Ge4 (RE = Ce, Pr, Nd; T = Nb, Ta) – A New Coloring Variant of the Aristotype AlB2

“…The Ce 3 TaRh 4 Ge 4 structure fits into the group-subgroup tree of the aristotype AlB 2 , [20,21] similar to many of the equiatomic CeTX phases (T = electron-rich transition metal; X = element of the 3rd, 4th, or 5th main group). [22,23] In contrast to the equiatomic compounds we observe two different colorings for Bärnighausen formalism [24][25][26] is presented in Figure 2.…”