Structural Complexity in the Apparently Simple Crystal Structure of Be₂ Ru

The structural features of the hexagonal layered crystal structure of Be₂ Ru (a=5.7508(3) Å, c=3.0044(2) Å, space group P $\bar{6}$ 2m) 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 Fe₂ 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 Be₂ 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 Be₂ Ru shows metal behaviour in agreement with the non-zero DOS at the Fermi level.