Electron-deficient Eu(6.5)Gd(0.5)Ge6 intermetallic: a layered intergrowth phase of the Gd5Si4- and FeB-type structures

A novel electron-poor Eu(6.5)Gd(0.5)Ge? compound adopts the Ca?Sn?-type structure (space group Pnma, Z = 4, a = 7.5943(5) ?, b = 22.905(1) ?, c = 8.3610(4) ?, and V = 1454.4(1) ?3). The compound can be seen as an intergrowth of the Gd?Si?-type (Pnma) R?Ge? (R = rare earth) and FeB-type (Pnma) RGe compounds. The phase analysis suggests that the Eu(7-x)Gd(x)Ge? series displays a narrow homogneity range of stabilizing the Ca?Sn? structure at x ≈ 0.5. The structural results illustrate the structural rigidity of the 2(∝)R?X?] slabs (X = p-element) and a possibility for discovering new intermetallics by combining the 2(∝)R?X?] slabs with other symmetry-approximate building blocks. Electronic structure analysis suggests that the stability and composition of Eu(6.5)Gd(0.5)Ge? represents a compromise between the valence electron concentration, bonding, and existence of the neighboring EuGe and (Eu,Gd)?Ge? phases.