The ternary system Hf–Al–Sn: isothermal section of the phase diagram at 600°C and crystal structures of the compounds

Chem. Met. Alloys 16 (2023) 26-31

Danylo MARYSKEVYCH, Yaroslav TOKAYCHUK, Roman GLADYSHEVSKII

https://doi.org/10.30970/cma16.0436

The isothermal section at 600°C of the phase diagram of the ternary system Hf–Al–Sn was constructed in the whole concentration range, using X-ray powder diffraction and energy-dispersive X-ray spectroscopy. A limited solid solution of inclusion type (up to 11.1 at.% Al), based on the binary compound Hf₅Sn₃, forms in the system. The crystal structure of Hf₅AlSn₃ (boundary composition of the solid solution Hf₅Al_xSn₃) belongs to the structure type Hf₅CuSn₃ (Pearson symbol hP18, space group P6₃/mcm, a = 8.5594(15), c = 5.7996(12) Å, Z = 2), which is a ternary filled-up variant of the structure type Mn₅Si₃, to which the structure of the binary compound Hf₅Sn₃ belongs. Three ternary compounds exist at 600°C: HfAl_2.636(2)Sn_0.364(2) (structure type ht-TiAl₃, tI8, I4/mmm, a = 3.95575(10), c = 8.9473(2) Å, Z = 2), Hf₅Al_2.70(4)Sn_0.30(4) (Mn₅Si₃, hP16, P6₃/mcm, a = 8.0910(6), c = 5.6515(4) Å, Z = 2), and Hf₅Al_{1.33(3)-0.782(10)}Sn_{1.67(2)-2.218(10)} (Nb₅SiSn₂, tI32, I4/mcm, a = 10.9331(9)-11.0348(6), c = 5.5012(5)-5.5611(3) Å, Z = 4). The structure of HfAl_2.64Sn_0.36 is derived from the cubic close-packed structure and the coordination polyhedra are cuboctahedra.

Isothermal section of the phase diagram of the ternary system Hf–Al–Sn at 600°C.

Keywords

Hafnium / Aluminum / Tin / X-ray powder diffraction / Phase diagram / Solid solution / Ternary compound / Crystal structure