Ternary erbium chromium sulfides: Structural relationships and magnetic properties

Abstract

Single crystals of four erbium - chromium sulfides have been grown by chemical vapor transport using iodine as the transporting agent. Single-crystal X-ray diffraction reveals that in Er3CrS6 octahedral sites are occupied exclusively by Cr3+ cations, leading to one-dimensional CrS4 5- chains of edge-sharing octahedra, while in Er 2CrS4, Er3+, and Cr2+ cations occupy the available octahedral sites in an ordered manner. By contrast, in Er 6Cr2S11 and Er4CrS7, Er3+ and Cr2+ ions are disordered over the octahedral sites. In Er2CrS4, Er6Cr2S 11, and Er4CrS7, the network of octahedra generates an anionic framework constructed from M2S5 slabs of varying thickness, linked by one-dimensional octahedral chains. This suggests that these three phases belong to a series in which the anionic framework may be described by the general formula [M2n+1S 4n+3]x-, with charge balancing provided by Er3+ cations located in sites of high-coordination number within one-dimensional channels defined by the framework. Er4CrS7, Er 6Cr2S11, and Er2CrS4 may thus be considered as the n = 1, 2, and ∞ members of this series. While Er4CrS7 is paramagnetic, successive magnetic transitions associated with ordering of the chromium and erbium sub-lattices are observed on cooling Er3CrS6 (Tc(Cr) = 30 K; T c(Er) = 11 K) and Er2CrS4 (TN(Cr) = 42 K, TN(Er) = 10 K) whereas Er6Cr2S 11 exhibits ordering of the chromium sub-lattice only (TN = 11.4 K).