Synthesis, crystal and electronic structure, physical properties and 121Sb and 151Eu Mössbauer spectroscopy of the Eu14AlPn11 series (Pn = As, Sb)

Abstract

The pnictides Eu₁₄AlAs₁₁ and Eu₁₄AlSb₁₁ were synthesized from the elements in sealed niobium ampoules. They crystallize in the tetragonal crystal system (Eu₁₄AlAs₁₁: a = 1627.6(2), c = 2180.0(4) pm; Eu₁₄AlSb₁₁: a = 1725.6(2), c = 2289.7(7) pm) with space group I4₁/acd, isostructural to Ca₁₄AlSb₁₁ and can be described as Zintl phases. The Al atoms are surrounded by four pnictogen atoms, forming [AlPn₄]⁹⁻ tetrahedra. Additionally isolated Pn³⁻ anions and linear Pn₃⁷⁻ trimers can be found in the crystal structure. The compounds can be described according to (Eu²⁺)₁₄(AlPn⁹⁻)(Pn³⁻)₄(Pn₃⁷⁻). Eu₁₄AlAs₁₁ and Eu₁₄AlSb₁₁ both exhibit an antiferromagnetic transition at T_N = 10.5(1) K and 12.5(1) K, respectively. For the antimonide, the magnetic transition has been confirmed by additional heat capacity measurements. Resistivity investigations indicate that Eu₁₄AlSb₁₁ is a semiconductor with a band gap of E_g = 0.28(5) eV close to room temperature. According to the Zintl formalism, the Eu atoms are divalent, which has been confirmed by magnetic susceptibility and additional ¹⁵¹Eu Mössbauer spectroscopic studies. The measurements conducted at 6 K, below the magnetic ordering temperature, show a full hyperfine field splitting with complex spectra underlining the recorded magnetic data. Furthermore, ¹²¹Sb Mössbauer spectroscopic studies have been conducted to study the different antimonide entities in the title compounds.