RE16AuxAl13−x with RE = La–Nd, Sm (x ≤ 3.37): synthesis, crystal structure and physical properties of an intermetallic solid solution with barrelane analogue units

Abstract

During phase analytical investigations in the rare-earth element rich side of the ternary system cerium–gold–aluminum, the new ternary rare-earth (RE) gold aluminides with a composition of RE₁₆Au_xAl_13−x (RE = La–Nd, Sm, x ≤ 3.37) have been synthesized first by reactive eutectics of RE/Au with Al. Single crystals of high quality can be obtained by this method. The title compounds can be selectively prepared by annealing arc-melted beads of appropriate composition below the peritectic point of the respective system. Like prototypic La₁₆Al₁₃, the representatives of the solid solution RE₁₆Au_xAl_13−x (RE = La–Nd, Sm; x ≤ 3.37) crystallize in the hexagonal crystal system (space group P2m, a = 916.6–890.4 pm, c = 1122.4–1090.1 pm) with one formula unit per unit cell. Single crystal investigations revealed Au/Al mixing on three of the four crystallographic aluminum sites. These sites form an empty (Au/Al)₁₁ barrelane analogous unit, coordinated solely by the respective rare-earth atoms. In addition one independent Al site with a fivefold capped trigonal prismatic arrangement, a so called Edshammar polyhedron, exists. Magnetic measurements of Ce₁₆Au₃Al₁₀ revealed two antiferromagnetic transitions with Neél-temperatures of 7.7(1) and 2.7(1) K and a magnetic moment of μ_eff = 2.48(1) μ_B, Pr₁₆Au₃Al₁₀ shows ferromagentic ordering with a Curie-temperature of 19.8(1) K and a magnetic moment of μ_eff = 3.58(1) μ_B.