Mixed-Valence State of Europium in the Misfit Layer Compound (EuS)1.173NbS2

A new misfit layer compound (EuS) 1.173 NbS 2 was synthesized, and its structure was solved in a (3+1) D superspace using the superspace group Xm 2 m( α 00 ) with X referring to a pseudo F centering. The cell parameters are a s = 3.3251(9) Å, b s = 5.7432(9) Å, and c s = 22.939(5) Å ( V s = 438.1(3) Å 3 ) with a modulation vector q = 0.5867(2) a s *. This compound is built from a regularly alternated stacking of [EuS] slabs (NaCl structure type with two atomic layers) and [NbS 2 ] slabs (NbS 2 structure type). Mössbauer and XPS spectroscopies as well as magnetic measurements clearly indicate a mixed-valence state for europium with a ratio Eu 2+ /Eu 3+ close to 40:60. Bond valence calculations taking into account the modulation of the Eu−S distances ascertain the mixed valence state of europium and indicate that Eu 2+ and Eu 3+ ions occupy the same crystallographic site. Moreover, Mössbauer spectra demonstrate that a charge hopping between Eu 2+ and Eu 3+ takes place above room temperature. The misfit layer (EuS) 1.173 NbS 2 can be considered as an inhomogeneous mixed-valence compound. Resistivity measurements show that (EuS) 1.173 NbS 2 behaves as a metal and at 3.5 K a strong decrease of the resistivity is observed conjointly with a ferromagnetic transition.