The Y5-xMg24+x(1.08(4)≤x≤1.30(1)) series and a ternary derivative Ce6.9Y12.5(7)Mg92.2: A comparison of their crystal and electronic structures

Abstract

The Y5-xMg24+x series and a ternary derivative, Ce0.36Y0.64(2)Mg4.76, have been synthesized using high-temperature methods and characterized by both powder and single crystal X-ray diffraction. The Y5-xMg24+x series upon quenching from 580°C crystallizes over the range 1.08(4)≤x≤1.30(1) in the cubic α-Mn structure type (I4-3m, Z=2, Pearson symbol cI58) with mixed occupancy of Y and Mg at the 8c site. As Mg content increases, the corresponding lattice parameter a increases from 11.2337(6)Å for Y3.92(4)Mg25.08 to 11.256(2)Å for Y3.70(1)Mg25.30. Attempts to replace Y atoms with larger, isovalent Ce atoms yielded Ce6.9Y12.5(7)Mg92.2(=Ce0.36Y0.64(2)Mg4.76), which adopts a defect Sm11Cd45 structure type (F4-3m, Z=8, Pearson symbol cF446.4), with a lattice parameter a=22.443(2)Å that is nearly twice larger than those of the Y5-xMg24+x series. The complex crystal structure of this ternary derivative can be described as an ordered, body-centered cubic packing of four chemically and structurally distinctive "nested-polyhedra," two 27-atom and two 29-atom, α-Mn units. Electronic structure calculations show nearly free electron like behavior, but with a distinctive pseudogap in the density of states curve for the ternary system. © 2013 Elsevier Inc.