Crystal structure of a solid solution in the Mg–Pd–Al system

Chem. Met. Alloys 12 (2019) 29-32

https://doi.org/10.30970/cma12.0391

Vasyl STOTSKYI, Svitlana PUKAS, Roman GLADYSHEVSKII

A search for new ternary palladium aluminides was carried out in the system Mg–Pd–Al. A new phase was observed in two alloys of nominal compositions Mg_7.1Pd_28.6Al_64.3 and Mg_11.1Pd_33.3Al_55.6; phase and structural analyses were performed based on X-ray powder diffraction data. A crystal structure corresponding to partial substitution of Mg in the binary compound Pd₈Al₂₁ (Pt₈Al₂₁-type, Pearson symbol tI116, space group I4₁/a) was established. The approximate composition Mg₅Pd₈Al₁₆ was determined by energy-dispersive X-ray spectroscopy for the phase in the Mg-poor sample (a = 13.0429(2), c = 10.6880(1) Å) and it was assumed, based on geometrical arguments, that Mg atoms replace Al atoms in Wyckoff position 4a and one of the seven positions 16f. The phase in the Mg-rich sample (a = 13.1928(4), c = 10.6488(5) Å) was found to contain more Mg, indicating the existence of a solid solution. Compared to the binary compound Pd₈Al₂₁, the a-parameter is also larger but the c-parameter shorter, leading to an overall increase of the cell volume with increasing Mg content.

Projection of the structure of Mg₅Pd₈Al₁₆ along [001].

Keywords

Ternary palladium aluminide / X-ray powder diffraction / Energy-dispersive X-ray spectroscopy / Crystal structure