Temperature-dependent diffraction studies on the stannides Sr₃Rh₄Sn₄, Sr₃Ir₄Sn₄ and Sr_2.43Eu_0.57Ir₄Sn₄

Abstract The stannides Sr 3 Rh 4 Sn 4 and Sr 2.43 Eu 0.57 Ir 4 Sn 4 (Na 3 Pt 4 Ge 4 -type, space group I <m:math xmlns:m="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <m:mrow> <m:mover accent="true"> <m:mn>4</m:mn> <m:mo>‾</m:mo> </m:mover> </m:mrow> </m:math>3 m ) were synthesized by induction-melting of the elements in sealed tantalum tubes followed by an annealing sequence to increase the crystallinity. Their polycrystalline samples were characterized by powder X-ray diffraction and the structures were refined from single crystal X-ray diffractometer data. The basic building units are [Rh 4 Sn 4 ] respectively [Ir 4 Sn 4 ] stellae quadrangulae which condense to rigid three-dimensional networks. A striking crystal chemical feature of the Na 3 Pt 4 Ge 4 -type phases are pronounced anisotropic displacements of the divalent cations. Additional structure refinements of Sr 3 Rh 4 Sn 4 and Sr 2.43 Eu 0.57 Ir 4 Sn 4 and the previously reported stannide Sr 3 Ir 4 Sn 4 at 90 K reveal less anisotropic behavior in going to lower temperatures.