Structural Complexity in the Apparently Simple Crystal Structure of Be₂Ru

Abstract

The structural features of the hexagonal layered crystal structure of Be 2 Ru (a = 5.7508(3) Å, c = 3.0044(2) Å, space group P � 62m) were investigated by single crystal X-ray diffraction and transmission electron microscopy (TEM). The residual electron density and high-resolution TEM images show that the real structure can be described as an intergrowth of the main hexagonal matrix of the Fe 2 P type with minor orthorhombic inclusions of its stacking variants. Such atomic arrangement is stabilized by the charge transfer from Be to Ru and by a system of polar three-and four-atomic bonds involving both components. The calculated electronic density of states (DOS) of Be 2 Ru revealed, contrarily to typical intermetallic compounds, a pseudo gap (dip) in the vicinity of the Fermi level. The temperature dependence of the electrical resistivity of Be 2 Ru shows metal behaviour in agreement with the non-zero DOS at the Fermi level.

Charge Transfer in Be−Ru Compounds

“…The final refinement results in the occupancy factor of 0.984(1) for Ru7 and 0.016(1) for the Ru8 positions (Tables 3 and 5). The additional position observed in Be 12 Ru 7 structure, exhibits striking similarities to those previously documented in Be 2 Ru [6a] . Indeed, in the latter, a similar additional position was observed both from single crystal data and atomic‐resolution electron microscopy, leading to a description of an intergrowth between the primary hexagonal matrix of Fe 2 P and minor orthorhombic inclusions of its stacking variants.…”

“…Structure organization . All three crystal structures can be described as an alternation of planar Be layers (A) with layers (B) formed by Ru atoms and one Be atom (Figure 2, left panel), a similar situation observed already in the crystal structure of Be 2 Ru (structure type Fe 2 P) [6a] …”

“…The Be−Ru binary system was initially investigated in the 1960 s [8] with more recent studies done on the binary compounds Be 2 Ru [6a] and Be 3 Ru [6b] . The present work reports results of X‐ray diffraction, metallography and thermal analysis showing that, in contrast to what has been reported in literature, [8] Be 3 Ru 2 crystallizes with a U 3 Si 2 ‐type structure [9] .…”

“… Two‐dimensional Fe 2 P−U 3 Si 2 intergrowth structures in the Be−Ru system: (top left) Crystal structure of Be 2 Ru (Fe 2 P type) [6a] . (top right) Crystal structure of Be 3 Ru 2 (U 3 Si 3 type).…”

“…From this perspective, the study of the Be−Ru system appears to be highly intriguing due to its similarities with the Al−Pt system. Indeed, Ru is a transition metal with properties similar to Pt, and its effective QTAIM charge in the studied compounds should be negative, regardless of their composition [6a,b] . Furthermore, Be, despite belonging to the second group of Periodic Table (alkaline earth metals), shares certain characteristics with aluminum, with which it is diagonally related [6e] …”