Crystal structures of the phases in the DyNi₃Al₉‒DyNi₃Ga₉ system

Chem. Met. Alloys 17 (2024) 24-31

Oleh LESKO, Nataliya MUTS, Yaroslav TOKAYCHUK, Roman GLADYSHEVSKII

https://doi.org/10.30970/cma17.0441

The subsystem DyNi₃Al₉‒DyNi₃Ga₉ was investigated by X-ray powder diffraction. Both boundary compounds crystallize with the partly ordered DyNi₃Al₉ type (Pearson symbol hR99, space group R32), which contains monoatomic layers with single rare-earth atoms and (Al,Ga)₃ triangles in the ratio 2:1. The solid solutions based on the ternary compounds were found to extend to the limiting compositions DyNi₃(Al_0.82Ga_0.18)₉ (a = 7.2589(1), c = 27.4045(6) Å) and DyNi₃(Al_0.44Ga_0.56)₉ (a = 7.24477(9), c = 27.4508(4) Å), respectively, at 600°C. Complete refinements were performed for several compositions. The samples contained in addition variable amounts of a Ni₂(Al,Ga)₃ phase with Ni₂Al₃-type structure and a new phase. The crystal structure of the new quaternary compound Dy_0.67Ni₂(Al,Ga)₅ was refined from X-ray powder diffraction data and was found to belong to the structure type Sc_0.6Fe₂Si_4.9 (Pearson symbol hP20, space group P6₃/mmc). The homogeneity range extends from the composition Dy_0.67Ni₂(Al_0.74Ga_0.26)₅ to Dy_0.67Ni₂(Al_0.31Ga_0.69)₅ at 600°C and the unit-cell parameters change from a = 4.19886(9), c = 15.8614(4) Å for the former to a = 4.17494(7), c = 15.9229(4) Å for the latter. It follows that the cell volume increases when Ga atoms are replaced by Al atoms.

Observed, calculated and difference (bottom) X-ray powder diffraction patterns for the DyNi₃Al₉ sample.

Keywords

Dy‒Ni‒Al‒Ga system / X-ray diffraction / Crystal structure / Aluminides