Electron-Deficient Eu6.5Gd0.5Ge6 Intermetallic: A Layered Intergrowth Phase of the Gd5Si4- and FeB-Type Structures

A novel electron-poor Eu(6.5)Gd(0.5)Ge₆ compound adopts the Ca₇Sn₆-type structure (space group Pnma, Z = 4, a = 7.5943(5) Å, b = 22.905(1) Å, c = 8.3610(4) Å, and V = 1454.4(1) ų). The compound can be seen as an intergrowth of the Gd₅Si₄-type (Pnma) R₅Ge₄ (R = rare earth) and FeB-type (Pnma) RGe compounds. The phase analysis suggests that the Eu(7-x)Gd(x)Ge₆ series displays a narrow homogneity range of stabilizing the Ca₇Sn₆ structure at x ≈ 0.5. The structural results illustrate the structural rigidity of the ²(∝)[R₅X₄] slabs (X = p-element) and a possibility for discovering new intermetallics by combining the ²(∝)[R₅X₄] slabs with other symmetry-approximate building blocks. Electronic structure analysis suggests that the stability and composition of Eu(6.5)Gd(0.5)Ge₆ represents a compromise between the valence electron concentration, bonding, and existence of the neighboring EuGe and (Eu,Gd)₅Ge₄ phases.