Synthesis, structure, and magnetic characterization of Cr4US8

https://doi.org/10.1016/j.jssc.2015.10.009Get rights and content

Highlights

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    At 1073 K Cr4US8 was synthesized and at 100 K its crystal structure was determined.

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    The 3D structure comprises CrS6 octahedra with channels partially occupied by U.

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    The magnetic behavior of Cr4US8 is complex.

Abstract

The compound Cr4US8 has been synthesized at 1073 K and its crystal structure has been determined at 100 K. The structure is modulated with a two-fold commensurate supercell. The subcell may be indexed in an orthorhombic cell but weak supercell reflections lead to the monoclinic superspace group P21/c(α0γ)0s with two Cr sites, one U site, and four S sites. The structure comprises a three-dimensional framework of CrS6 octahedra with channels that are partially occupied by U atoms. Each U atom in these channels is coordinated by eight S atoms in a bicapped trigonal-prismatic arrangement. The magnetic behavior of Cr4US8 is complex. At temperatures above ~120 K at all measured fields, there is little difference between field-cooled and zero field-cooled data and χ(T) decreases monotonously with temperature, which is reminiscent of the Curie–Weiss law. At lower temperatures, the temperature dependence of χ(T) is complex and strongly dependent on the magnetic field strength.

Graphical abstract

Introduction

Uranium chalcogenide compounds that contain 3d metals are of considerable interest because of the possible interactions between the 3d and localized 5f electrons [1], [2], [3], [4], [5]. Whereas a significant number of ternary uranium chalcogenides have been synthesized [6], [7], [8], most that contain 3d metals belong to one of a few compositions. These compositions include MUQ3 (M=Sc, V–Ni; Q=S, Se) [9], [10], [11], [12], [13], [14], [15], [16], [17], MU8Q17 (M=Sc–Ni; Q=S, Se) [9], [10], [11], [18], [19], [20], [21], [22], MU2Q5 (M=Ti, Fe, Co; Q=S, Se) [10], [11], [23], [24], and MU3S6 (M=Sc, Ti) [24], [25]. Compounds that are not among these compositions include Cu2U3Q7 (Q=S, Se) [26] and Cu2U6Q13 (Q=S, Se) [27], [28]. Note that all these compositions have U:M>1 and are uranium rich. There appear to have been no ternary 3d metal-rich compounds reported.

However, a number of ternary 4d and quaternary 3d metal-rich uranium compounds are known. These include Mo6UQ8 (Q=S, Se) [29], UxPd3S4 (0.9<x<1.0) [30], Pd2US4 [31], Y4US7 [32], Ba2Cu2US5 [33], Ba4Cr2US9 [34], ACu12U2S15 (A=K, Rb, Cs) [35], [36], and K2Cu3US5 [37]. It seems reasonable that ternary 3d metal-rich uranium chalcogenides should exist, but that exploration of such phases is lacking. We present here the synthesis and characterization of Cr4US8, a ternary 3d-metal-rich uranium chalcogenide.

Section snippets

Synthesis

The following reactants were used as received: Cr (Aesar, 99.99%), S (Mallinckrodt, 99.6%), and PbI2 (Aldrich, 99%). U powder was obtained through the hydridization of depleted U turnings (IBI Laboratories) followed by decomposition of the hydride under vacuum [38]. The reactants were loaded into carbon-coated fused-silica tubes in an Ar-filled glovebox, evacuated to 10−4 Torr, and then flame sealed.

Black crystals of Cr4US8 were obtained from the reaction of U (0.0300 g, 0.126 mmol), Cr (0.0065 g,

Synthesis

In an attempt to synthesize a new Cr/U/S phase, crystals of Cr4US8 were obtained as rectangular black prisms from the reaction of the elements in a PbI2 flux at 1073 K. PbI2 (m.p. 675 K) was chosen over other low-melting fluxes because Pb2+ is a soft acid and I− is a softer base than S2− and hence incorporation of these ions in the final product was thought to be unlikely.

Structure

The subcell structure of Cr4US8 crystallizes with two formula units in space group D2h16–Pmcn of the orthorhombic system. The

Conclusions

The compound Cr4US8 has been synthesized at 1073 K by the reaction of the elements in a PbI2 flux. Its crystal structure has been determined at 100 K. The structure is commensurately modulated with a modulation vector q=1/2a*. The subcell may be indexed in an orthorhombic cell in space group D2h16–Pmcn but weak supercell reflections lead to the monoclinic superspace group P21/c(α0γ)0s with two Cr sites, one U site, and four S sites. The structure comprises a three-dimensional framework of CrS6

Supporting information

Supplementary data associated with this article can be found in the online version at 10.1016/j.jssc.2015.10.009. The crystallographic data in CIF format for Cr4US8 have been deposited with FIZ Karlsruhe as CSD number 429728. These data may be obtained free of charge by contacting FIZ Karlsruhe at +497247808666 (fax) or [email protected] (email).

Acknowledgments

This research was supported at Northwestern University by the U.S. Department of Energy, Basic Energy Sciences, Chemical Sciences, Biosciences and Geosciences Division and Division of Materials Science and Engineering Grant ER-15522. Use was made of the IMSERC X-ray facility at Northwestern University, supported by the International Institute of Nanotechnology. C.D.M. was supported by the U.S. Department of Energy, Office of Basic Energy Sciences under Contract no. DE-AC02-06CH11357. A portion

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