Crystal structure of the ternary compounds T2AlSb3 (T = Zr, Hf)

New ternary compounds Zr 2 AlSb 3 and Hf 2 AlSb 3 were synthesized from the high-purity metals (zirconium > 99.95 mass %, hafnium > 99.95 mass %, Al > 99.99 mass %, antimony > 99.97 mass %) by arc melting in a water-cooled copper crucible with a tungsten electrode under a purified argon atmosphere, using Ti as a getter. The ingots were annealed at 600 °C in a quartz ampoule under vacuum for 1 month and subsequently quenched into cold water. The compositions of the synthesized alloys were confirmed by X-ray fluorescence spectral analysis carried out on ElvaX Pro analyzer. Phase and structure analyses were carried out using X-ray powder diffraction patterns collected at room temperature on a PROTO AXRD Benchtop diffractometer (Cu K α-radiation, angular range 20° < 2 θ < 120°, step 0.015°) and a STOE Stadi P diffractometer equipped with a linear detector (Cu K α 1 -radiation, angular range 10° < 2 θ < 110°, step 0.015°). The crystal structure of the ternary compounds Zr 2 AlSb 3 and Hf 2 AlSb 3 were refined by the Rietveld method using the program package FullProf Suite. The crystal structures ternary compounds Zr 2 AlSb 3 and Hf 2 AlSb 3 belong to the structure type Zr 2 CuSb 3 , Pearson symbol tP 6, space group P -4 m 2 ( a = 3.91644(6), с = 8.72525(13) Å, R B = 0.0324 for Zr 2 AlSb 3 and a = 3.9021(2), с = 8.6510(5) Å, R B = 0.0382 for Hf 2 AlSb 3 ). The structures are characterized by an ordered arrangement of atoms and by the absence of homoatomic contacts in the closest coordination environment. T (Hf or Zr) atoms are coordinated by seven Sb atoms and two Al atoms forming tricapped trigonal prisms of the composition Al 2 Sb 7 . The coordination polyhedra of the Al and Sb2 atoms are formed by eight atoms as double trigonal prisms, forming the gyrobifastigium of compositions T 4 Sb 4 and T 4 Al 4 , respectively. The closest environment of the Sb1 atoms is represented by five T atoms forming a square pyramid T 5 . The structure type Zr 2 CuSb 3 belongs to the family of linear intergrowth structures composed of BaAl 4 -type slabs (layers of centered tetragonal antiprisms) and W-type slabs (layers of empty “half octahedra”). Keywords : zirconium, hafnium, aluminum, antimony, ternary compound, X-ray powder diffraction, crystal structure, intergrowth structure.