Synthesis and Properties of Ba₆Fe₂Te₃S₇, with an Fe Dimer in a Magnetic Singlet State

Abstract

A new quaternary sulfide telluride, Ba 6 Fe 2 Te 3 S 7 , was synthesized by a solid-state reaction, and its crystal structure is novel. X-ray diffraction data on powder and single crystals reveal an orthorhombic lattice with a = 9.7543(3) Å, b = 18.2766(6) Å, and c = 12.0549(4) Å, and the noncentrosymmetric space group Cmc2 1 (No. 36). The properties of the compound were studied by magnetic susceptibility investigations, specific heat measurements, Mossbauer spectroscopy, and density functional theory calculations. Assuming Ba 2+ and, as verified by the Mossbauer spectra, Fe 3+ , the charge balance requires the presence of a polytelluride, suggested to be a straight-chain [Te 34− ] polyanion. Further, the crystal structure contains [Fe 2 S 7 ] 8− dimers of two vertex-sharing tetrahedra, with a nearly linear Fe−S− Fe atom arrangement. The dimer exhibits antiferromagnetic coupling, with a coupling constant J = −10.5 meV (H = −2JS 1 S 2 ) and S = 5/2, resulting in a spin singlet ground state. The interdimer magnetic interaction is so weak that the magnetic dimers can be treated as individuals.

Synthesis and Properties of BaMTeS (M = Fe, Mn, Zn) and the Disordered Structural Analog BaGe0.5TeS

“… 11 The lack of both paramagnetic and ordered behavior in BaFeTeS suggests that a thermal activation mechanism of electron states could be the cause of the observed susceptibility behavior. An example of such behavior occurs, for instance, in the related Ba 6 Fe 2 Te 3 S 7 phase, 21 although the Fe structure of Ba 6 Fe 2 Te 3 S 7 is dimeric, rather than planar as in BaFeTeS.…”

“…The low synthesis temperature was necessitated by the fact that BaFeTeS constitutes the low-temperature phase of the Ba−Fe−Te−S phase system. Running the synthesis at a higher temperature risked irreversible formation of the intermediate temperature Ba 6 Fe 2 Te 3 S 7 21 phase or a yet unreported high-temperature phase in the same system. 22 The synthesis of single crystals for the other three phases utilized the same BaS and Te sources.…”