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