Crystal structure of the ternary phase ErAl2.88Sn0.12

The ternary phase ErAl 2.88 Sn 0.12 was synthesized by arc melting from high-purity metals (Er >99.9 mass %, Al > 99.99 mass %, Sn > 99.99 mass %), using a water-cooled copper hearth and tungsten electrode under an argon atmosphere, purified by using Ti sponges as a getter. For homogenization aloe was sealed in quartz ampoule under vacuum and annealed at 600° C for 720 h. Finally, the ampoule with the sample was quenched into cold water. The composition of the synthesized alloy was confirmed by X-ray fluorescence spectral analysis carried out on ElvaX Pro analyzer. Crystal structure of the ternary phase ErAl 2.88 Sn 0.12 (refined composition ErAl 2.879(4) Sn 0.121(4) ) was determined by X-ray powder diffraction by using the pattern, collected at room temperature on the diffractometer STOE Stadi P (Cu K α 1 -radiation, angular range 6° ≤ 2 θ ≤ 109.420°, step 0.015°). The profile and structural parameters were refined by the Rietveld method, using the program package FullProf Suite. Structure belongs to the structure type HoAl 3 , Pearson symbol hR 60, space group R -3 m , a = 6.0678(3), c = 35.8620(16) Å, R B = 0.0332) and is characterized by a disordered distribution of p -element atoms in three independent crystallographic positions. Er atom occupy three sites (two positions 6 c and one position 3 a ), and р -element atoms (Al and Sn) form statistical mixtures in other three positions (two 18 h and one 9 e ). Rhombohedral unit cell contains 15 formula units (60 atoms). Calculated interatomic distances within the coordination polyhedra of atoms ( δ Er– M = 2.9609(9)–3.076(3) Å, δ M – M = 2.761(3)–3.068(3) Å) correspond to the sum of the atomic radii of Er, Al, and Sn, which may indicate the dominance of the metallic type of bonding for ErAl 2.88 Sn 0.12 . Structure type HoAl 3 belongs to the family of close-packed structures and is built of 15 monatomic layers with triangular meshes, stacked along the crystallographic direction [001] in the sequence ( hchcc ) 3 . Coordination polyhedra of atoms are cuboctahedra and anticuboctahedra. Keywords : erbium, aluminum, tin, ternary phase, X-ray powder diffraction, crystal structure, close-packing of atoms.