Al15Ge4Ni3: A new intergrowth structure with Cu3Au- and CaF2-type building blocks

• The crystal structure of Al15Ge4Ni3 (space group I4̄3m) was determined.
• It shows a unique combination of CaF2- and Cu3Au-type building blocks.
• Electronic (DFT) calculations were performed to gain insight to chemical bonding.

The new ternary compound Al15Ge4Ni3 (τ2 in the system Al–Ge–Ni) was synthesized in single crystalline form by a special annealing procedure from samples located in the three phase fields [L+Al+τ2] and [L+Ge+τ2]. The crystal structure of Al15Ge4Ni3 was determined by single-crystal X-ray diffraction. The compound crystallizes in a new structure type in space group I4̄3m, Pearson Symbol cI88, cubic lattice parameter a=11.405(1) Å. Phase diagram investigations indicate stoichiometric composition without considerable homogeneity range; τ2 melts peritectically at T=444 °C. The crystal structure of Al15Ge4Ni3 shows a unique combination of simple Cu3Au- and CaF2-type building blocks: a three dimensional network of CaF2-type units, formed by Ni and Al atoms, is interspaced by clusters (Al6Ge8) resembling unit cells of the Cu3Au-type. Both structural motifs are connected by Al–Ge bonds. The ground state energy of the compound was obtained by DFT calculations and the densities of states were analyzed in detail. In addition, electron density maps were calculated in four different sections through the unit cell using the full potential linearized augmented plane-wave (FLAPW) method. The bonding situation in Al15Ge4Ni3 was discussed combining results from electronic calculations with the analysis of the coordination of atoms.

The new compound Al15Ge4Ni3 shows a unique combination of simple Cu3Au- and CaF2-type building blocks.Figure optionsDownload as PowerPoint slide