Ternary Erbium Chromium Sulfides: Structural Relationships and Magnetic Properties

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 CrS45− chains of edge-sharing octahedra, while in Er2CrS4, Er3+, and Cr2+ cations occupy the available octahedral sites in an ordered manner. By contrast, in Er6Cr2S11 and Er4CrS7, Er3+ and Cr2+ ions are disordered over the octahedral sites. In Er2CrS4, Er6Cr2S11, 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+1S4n+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, Er6Cr2S11, 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; TC(Er) = 11 K) and Er2CrS4 (TN(Cr) = 42 K, TN(Er) = 10 K) whereas Er6Cr2S11 exhibits ordering of the chromium sub-lattice only (TN = 11.4 K).