Synthesis, Crystal and Electronic Structure of the Titanium Bismuthides Sr5Ti12Bi19+x, Ba5Ti12Bi19+x, and Sr5-EuTi12Bi19+x (x ≈ 0.5-1.0; ≈ 2.4, 4.0)

Crystals of the new ternary bismuthides AE(5)Ti(12)Bi(19+x) (AE = Sr, Ba) and Sr5-EuTi12Bi19+x ( approximate to 2.4, 4.0; x 1.0) were grown using an excess of molten Bi as a flux. The title compounds crystallize in the cubic non-centrosymmetric space group P3m and are structurally related to the antimonides Ba5M12Sb19+x (M = Ti, V, Nb). The crystal structure features Ti atoms stuffed in the -brass-like sub-lattice made of AE (AE = Sr, Ba, Eu) and Bi atoms. The arrangement of the AE atoms, on its own, represents a framework consisting of interconnected regular tetrahedra and octahedra. Another notable attribute of the AE(5)Ti(12)Bi(19+x) structure is the disordered Bi moiety located at the center of the unit cell and showing homoatomic Bi-Bi bonding. Electronic structure calculations and electrical resistivity measurements indicate metallic behavior of the new bismuthides. Magnetization measurements on samples of Sr5-EuTi12Bi19+x show paramagnetic behavior consistent with the 2+ ground state for Eu. The measurements also confirm no magnetic ordering down to 3 K, stemming from the geometrically frustrated exchange interactions of the Eu2+ cations.