Ternary gallide Zr7Pd7–xGa3+x (0 ≤ x ≤ 1.8): Synthesis, crystal and electronic structures

Abstract

The new ternary compound Zr₇Pd_7-xGa_3+x (0 ≤ x ≤ 1.8) was synthesized by arc melting the elements under argon and subsequent annealing the ingots at 870 K for 720 h. The polycrystalline samples were characterized by powder X-ray diffraction (XRD) and the crystal structure of the compound was determined from single crystal X-ray diffraction data. Zr₇Pd₇Ga₃ crystallizes with a ternary version of the Zr₇Ni₁₀ type of structure exhibiting statistical mixtures of palladium and gallium atoms on three crystallographically independent nickel sites (oS68, Cmce, a = 12.997(3), b = 9.623(2), c = 9.630(2) Ǻ, Z = 4, R1 = 0.033, wR2 = 0.067 for 719 unique reflections with I_o > 2σ(I_o) and 48 refined parameters). The crystal structure of Zr₇Pd₇Ga₃ is represented by a 3D Pd–Ga framework built of sinusoidal layers of Pd and Ga stacking along the b axis sandwiching the Zr atoms. The homogeneity range of the compound Zr₇Pd_7–xGa_3+x has been refined from powder XRD and EDX data: 0 ≤ x ≤ 1.8; variation of the lattice parameters is the following: a = 13.0174(8)–12.904(3), b = 9.6306(8)–9.559(8), c = 9.6348(8)–9.700(5) Å. Electronic structure calculations have been performed for an idealized model Zr₇Pd₁₀ as well as a model compound Zr₇Pd_6.5Ga_3.5 revealing that the Ga-free Zr₇Pd₁₀ is significantly destabilized by strong Pd–Pd anti-bonding interactions. Substitution of Pd by Ga reduces those, stabilizing Zr₇(Pd,Ga)₁₀ which features strong heteroatomic bonding between Zr and the Pd/Ga substructure, putting it into the class of polar intermetallics.