Synthesis, crystal and electronic structures, physical properties and 121Sb and 151Eu Mössbauer spectroscopy of the alumo-antimonide Zintl-phase Eu5Al2Sb6

Abstract

Eu₅Al₂Sb₆ was synthesized from the elements in niobium ampoules. It crystallizes in the orthorhombic crystal system (a = 1027.55(7), b = 1200.28(6), c = 1324.22(7) pm) with space group Pnma (no. 62), isostructural to Sr₅Al₂Sb₆, and can be described as a Zintl phase. The Al atoms are tetrahedrally surrounded by Sb atoms, forming branched strands. Besides Sb³⁻ anions, antimony Sb₂⁴⁻ dumbbells can also be found in the crystal structure. Eu₅Al₂Sb₆ [≡(Eu²⁺)₅(Al³⁺)₂(Sb³⁻)₄(Sb₂⁴⁻)] exhibits three magnetic ordering phenomena at T₁ = 12.3(1), T₂ = 10.6(1) and T₃ = 3.0(1) K, obtained by heat capacity measurements. While T₃ is of antiferromagnetic nature, T₁ and T₂ correspond to canted antiferromagnetic transitions. Resistivity investigations indicate that the title compound is a semiconductor, in line with the band structure calculations. Spin exchange parameters, calculated using mapping analysis, confirm that the magnetic phase transition at T_N = 3.5(1) is associated with the ordering of Eu1 atoms. The divalent character has been confirmed by ¹⁵¹Eu Mössbauer spectroscopic studies. Measurements conducted at 5 K show a hyperfine field splitting for two of the three Eu sites, underlining the magnetic data. Additionally, ¹²¹Sb Mössbauer spectroscopic studies have been conducted on Eu₅Al₂Sb₆ and isostructural Sr₅Al₂Sb₆.