CeCr ₂ Al ₂₀ -type phases <i>A</i> Ir ₂ Cd ₂₀ ( <i>A</i> = Sr, La–Nd, Sm, Eu) − structure and magnetic properties

Abstract The cadmium-rich intermetallic cage compounds A Ir 2 Cd 20 ( A = Sr, La–Nd, Sm, Eu) were synthesized by induction-melting of the elements in sealed tantalum ampoules followed by annealing in muffle furnaces. The polycrystalline samples were characterized through their Guinier powder patterns. The structures of LaIr 2 Cd 20 and EuIr 2 Cd 20 were refined from single crystal X-ray diffractometer data: CeCr 2 Al 20 -type, Fd <m:math xmlns:m="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <m:mrow> <m:mover accent="true"> <m:mn>3</m:mn> <m:mo>‾</m:mo> </m:mover> </m:mrow> </m:math> $\overline{3}$ m , a = 1,566.26(4) pm, w R = 0.0438, 514 F 2 values, 17 variables for LaIr 2 Cd 20 and a = 1,567.58(3) pm, w R = 0.0645, 438 F 2 values, 17 variables for EuIr 2 Cd 20 . The structures derive from a MgCu 2 -type A Ir 2 substructure where the A atoms are surrounded by 16 Cd atoms in form of a Frank-Kasper polyhedron and the Ir atoms have 12 Cd neighbors in icosahedral coordination. Temperature dependent magnetic susceptibility studies show diamagnetism for SrIr 2 Cd 20 and LaIr 2 Cd 20 . CeIr 2 Cd 20 , PrIr 2 Cd 20 and NdIr 2 Cd 20 are Curie-Weiss paramagnets without any sign for magnetic ordering down to 2 K. EuIr 2 Cd 20 contains stable divalent europium (7.85(1) µ B Eu atom −1 ) and orders ferromagnetically at T C = 17.2(1) K. The stable divalent ground state is corroborated by 151 Eu Mössbauer spectroscopy with an isomer shift value of δ = −10.66(1) mm s −1 .