Rare-earth transition-metal indium sulphides RE3FeInS7 (RE=La–Pr), RE3CoInS7 (RE=La, Ce), and La3NiInS7

• Six members of noncentrosymmetric sulphide series RE3MInS7 have been prepared.
• They are the first examples of chalcogenides RE3MM'Ch7 with In atoms in M' site.
• X-ray photoelectron spectra support the formulation (RE3+)3(M2+)(In3+)(S2−)7.
• Band structure calculations suggest semiconducting or metallic behaviour.

Six quaternary rare-earth-containing sulphides RE3MInS7 (M=Fe, Co, Ni) have been prepared by reactions of the elements at 1050–1150 °C. They are the first examples of chalcogenides RE3MM'Ch7 adopting related La3CuSiS7- or ordered Ce3Al1.67S7-type structures in which the M' component is indium. They crystallize in the noncentrosymmetric hexagonal space group P63 with Z=2 and cell parameters in the ranges of a=9.95–10.15 Å and c=6.25–6.29 Å for RE3FeInS7 (RE=La–Pr), RE3CoInS7 (RE=La, Ce), and La3NiInS7. The crystal structure consists of parallel chains of face-sharing M-centred octahedra and stacks of In-centred tetrahedra, all pointing in the same polar direction, with seven-coordinate La atoms in the intervening spaces. X-ray photoelectron spectra support the valence assignments implied by the formulation (RE3+)3(M2+)(In3+)(S2−)7. Magnetic measurements are suggestive of antiferromagnetic coupling between the M moments. Band structure calculations reveal that a band gap of 0.25 eV is present in La3FeInS7, whereas the increased electron count in La3CoInS7 and La3NiInS7 causes the Fermi level to cut narrow bands.

RE3MInS7 (M=Fe, Co, Ni) consists of chains of face-sharing M-centred octahedra and stacks of In-centred tetrahedra.Figure optionsDownload as PowerPoint slide