Elsevier

Intermetallics

Volume 11, Issue 6, June 2003, Pages 581-587
Intermetallics

Synthesis and crystal structures of RERhIn (RE=Sm, Tb, Ho, Er, Tm, Yb, Lu)

https://doi.org/10.1016/S0966-9795(03)00042-6Get rights and content

Abstract

The intermetallic rare earth metal compounds RERhIn (RE=Sm, Tb, Ho, Er, Tm, Yb and Lu) were synthesized from the elements by arc-melting, by reactions in sealed niobium tubes in a high-frequency furnace, or by induction melting in glassy carbon crucibles. All compounds were investigated by X-ray powder diffraction and the structures have been refined on the basis of single-crystal diffractometer data: ZrNiAl type, P6̄2m, a=750.93(8), c=397.52(4) pm, wR2=0.027, 273 Fo 2 values for SmRhIn, a=748.0(2), c=390.4(1) pm, wR2=0.054, 238 Fo2 values for TbRhIn, a=747.21(6), c=385.72(3) pm, wR2=0.036, 223 Fo2 values for HoRhIn, a=746.5(1), c=384.01(9) pm, wR2=0.040, 337 Fo2 values for ErRhIn, a=747.17(8), c=380.47(6) pm, wR2=0.029, 335 Fo2 values for TmRhIn, with 14 variables per refinement, and TiNiSi type, Pnma, a=692.9(3), b=414.1(2), c=849.0(3) pm, wR2=0.082, 591 Fo2 values for YbRhIn, a=690.3(1), b=413.12(8), c=848.2(2) pm, wR2=0.044, 589 Fo2 values for LuRhIn, with 20 variables per refinement. In both structure types, the rhodium and indium atoms build a three-dimensional [RhIn] network with strong Rh–In and In–In bonding in which the rare earth metal atoms fill distorted hexagonal channels. The switch in crystal structure from TmRhIn to YbRhIn is ascribed to geometrical effects. The crystal chemistry of these intermetallic compounds is briefly discussed.

Introduction

The ternary systems rare earth (RE) metal – rhodium – indium have first been investigated by Ferro and coworkers in Genova already in 1974 [1]. They report on the synthesis and X-ray powder characterization of RERhIn with RE=Y, La, Nd, Gd, Dy, and Er, while the cerium [2], praseodymium [3], and europium [4] compounds were described later. The course of the cell volumes indicates non-trivalent oxidation states for the cerium and europium atoms in CeRhIn [5], [6], [7], [8], [9] and EuRhIn [4], respectively, giving rise for interesting physical properties: CeRhIn is a mixed-valent Kondo compound and EuRhIn with purely divalent europium orders ferromagnetically at 22 K.

Within the series of RERhIn intermetallics not all compounds have yet been investigated. Especially the ytterbium compound is missing. This compound is of high interest since the YbTIn indides (T=transition metal) are potential candidates when screening for mixed valent compounds [10]. In the course of our systematic investigations of the ternary RE–Rh–In systems we prepared the missing RERhIn intermetallics and refined the structures with Sm, Tb, Ho, Er, Tm, Yb, and Lu as rare earth metal component. The syntheses and crystal chemistry of these materials is reported herein.

Section snippets

Synthesis

Starting materials for the preparation of the RERhIn intermetallics were ingots of the rare earth metals (Johnson Matthey), rhodium powder (Degussa-Hüls), and indium tear drops, all with stated purities better than 99.9%. In a first step, the rare earth metal ingots were cut into small pieces under dried paraffin oil. The latter was washed off with dried (over sodium wire) n-hexane and the pieces were melted to buttons (except ytterbium) in an arc-melting furnace [11] under an argon atmosphere.

Structure refinements

The isotypy of SmRhIn, TbRhIn, HoRhIn, ErRhIn, and TmRhIn with the ZrNiAl type (space group P6̄2m) [15], [16], [17], and YbRhIn and LuRhIn with the TiNiSi type (space group Pnma) [18] was already evident from the X-ray powder data. The atomic parameters of PrRhIn [3] and TiNiSi [18] were taken as starting positions and the seven structures were then successfully refined using Shelxl-97 [19] (full-matrix least-squares on Fo2) with anisotropic atomic displacement parameters for all atoms.

As a

Acknowledgements

We thank B. Heying, Dr. R.-D. Hoffmann, and Dipl.-Ing. U. Ch. Rodewald for the intensity data collections and the Degussa-Hüls AG for a generous gift of rhodium powder. This work was financially supported by the Fonds der Chemischen Industrie and the Deutsche Forschungsgemeinschaft. M.L. is indebted to the NRW Graduate School of Chemistry for a PhD stipend.

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