Evidence of a Mixed-Valence State for Europium in the Misfit Layer Compound [(EuS)1.5]1.15NbS2 by Means of a Superspace Structural Determination, Mössbauer Spectroscopy, and Magnetic Measurements

Crystal Structures and Magnetic Properties of the Two Misfit Layer Compounds: [SrGd0.5S1.5]1.16 NbS2 and [Sr(Fe,Nb)0.5S1.5]1.13 NbS2

“…However, it has to be recalled that such a structural approach was previously implemented for the parent 1:5Q=1H compound [(EuS) 1.5 ] 1.15 NbS 2 (9), which exactly corresponded to the example of the Sr-Gd derivative, considering their unit-cell parameters as well as their respective subspace groups; the good quality of the Eu-studied crystal had authorized such a study, in the super-space group G s ¼ Fm2mða; 0; 0Þ with a ¼ 0:5768; refinement converged to very low R values R=R w (%)=3.58/4.75. Therefore, the modulated structure was known, and subsequently the inter-atomic distances at the interface between the Q and the H-parts.…”

“…The stacking sequence corresponding to the m=n ¼ 2=1 ratio was recently encountered for a Pb/Sb misfit derivative of the natural franckeite type (7). But the most recent novelty refers to the characterization of a new member, labeled the 1:5Q=1H homolog (8,9). The structure of its Q-subpart is a three-atom-thick layer, which differs from an even-atom-thick one as this occurred in all the previous 1Q or 2Q misfit parents.…”

“…As a direct consequence, the situation of atoms in the median plane is not equivalent to that of atoms located on the surfaces for this ''1.5 Q-slab''. This authorizes either a difference between metal atoms occupying these sites, as for instance Fe in the central part and Pb at the border (8), or the same kind of metal atom but at different oxidation states as noticed with europium (occurrence of a mixed valence states: 2 Eu 2+ (external sheets) for 1 Eu 3+ (central sheet)) (9). The structure of the Pb-Fe 1.5Q-derivative shows that Fe atoms occupy a four-split position (distorted tetrahedral site) close around the central one (compressed octahedral site) also occupied by Fe (and minor Nb).…”

“…After this, and because of the complexity of the Fe-site distribution, we also prepared another material (Sr-Gd), with Gd 3+ ion substituting Fe 3+ in the median plane, knowing that only a single site (central site=octahedral) was observed in the corresponding Eu-1.5Q-derivative (9). This paper deals with syntheses and chemical analyses of these two Sr-Fe and Sr-Gd misfit compounds, their structure determinations, and their magnetic properties coupled with a M .…”

Quantification of the Interlayer Charge Transfer, via Bond Valence Calculation, in 2D Misfit Compounds: The Case of (Pb(Mn, Nb)0.5S1.5)1.15NbS2

“…1b), where the three-atom-thick Q layer alternates with the H layer. Such an homologue was "rst obtained with (Pb Fe S ) NbS (7,8), and [(EuS) ] NbS (9). In these two compounds, the charge transfer is clearly due to the presence of a trivalent cation in the central atomic plane of the Q layer.…”