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The hyperfine structure of the low-temperature Mossbauer spectra of dopant 119Sn4+ ions (0.4 at. %) in a fine crystalline MnO sample, characterized by X-ray diffraction and magnetic measurements, has been studied. The 119Sn spectra show that tin is distributed over positions with an inhomogeneous cationic environment. The appearance of such positions is explained by the local compensation for the excess charge of Sn4+ by manganese vacancies V Mn and segregation of defects resulting in precipitation of MnSnO3 clusters. The non-uniform distribution of Sn4+ and the related dependence of the number of broken magnetic bonds on the local tin concentration are responsible for the fluctuation of the T N values, which is “perceived” by 119Sn in different MnO crystallites. The 119Sn spectra exclude the possibility that tin enters into the composition of superpara-magnetic particles.

International audience; Synchrotron and Neutron Solutions to Oil Industry ProblemBulk and alumina-supported Mo0.5W0.5S2 compounds were prepared. The presence of both molybdenum and tungsten in every [MS2] layer (intralayer solid solution) was evidenced using EXAFS spectroscopy, the only local method which can provide such relevant structural information. The catalytic interest of such solid solution is to provide a continuous variation of M-S bond strength which is considered as the key parameter of the catalytic activity transition metal sulfides. The solid solution is maintained after promotion by Ni either on unsupported or supported state.

The interaction of MoS 2 single-layer dispersion with 1,10-phenanthroline has been studied over the pH range 0–11. Only protonated phenanthroline initiates flocculation of dispersion and formation of intercalation compounds. Two intercalated phases containing respectively 0.31–0.35 and 0.1 mol of phenanthroline per mol MoS 2 have been isolated. In the first one (interlayer spacing c = 14.92–15.56 A) the planar organic species are inclinated with respect to MoS 2 layers. In the second one ( c = 9.7 A) these moieties are oriented parallel to the layers.

The new mixed metal titanate Ba 2 Fe 2 Ti 4 O 13 ( 1 ) was obtained in crystalline form by heating a mixture of BaCO 3 , Fe 3 O 4 and TiO 2 at 1350°C for 48 h. Compound 1 was characterized by single-crystal X-ray diffraction methods. It is isomorphous to the related known compounds Na 2 Ti 6 O 13 and Ba 2 NiTi 5 O 13 . The X-ray diffraction and Mossbauer measurements of 1 obtained at room temperature indicate that the iron ions are unequally distributed between the three independent sites occupied by the transition metal ions.

Two different sites have been evidenced for SN(II) dopant atoms located at the surface of the Cr 2 O 3 substrate. Their inequivalence appears to be essentially due to the number of neighboring Cr(III) cations which are responsible for the magnetic hyperfine fields H transferred at the 119 Sn nuclei. While a large difference is observed in the saturation values of H, the isomer shift and quadrupole splitting—which are predominantly determined by tin-oxygen bonding—differ for the two sites to a lesser extent. Moreover, the main component V zz of the electric field gradient at 119 Sn nuclei is found, in both cases, to be negative and oriented at the same angle with respect to the c-axis of the Cr 2 O 3 lattice. The magnetic ordering temperature detected by the surface-located 119 Sn(II) atoms appears to be in good agreement with that previously determined from antiferromagnetic resonance experiments for undoped Cr 2 O 3 . The Goldanskii-Karyagin effect, which is observed for Sn(II) dopant atoms in the paramagnetic region, indicates that the mean square vibration amplitudes are smaller along the V zz axis than perpendicular to this direction.

Resume Magnetic hyperfine fields transferred at 119 Sn probe atoms (in both Sn(II) and Sn(IV) valence states) in antiferromagnetic α-MnS have been for the first time investigated. At 6 K, a unique hyperfine splitting pattern (H = 27 kOe) was observed for the Sn(II) substituant, isovalent with Mn(II), and two for the Sn(IV) heterovalent substituant (H 1 = 392 kOe and H 2 = 296 kOe). The charge compensation mechanism is shown to mainly involve Mn(II) vacancy location in the vicinity of Sn(IV), the two magnetically non-equivalent surroundings of Sn(IV) being related to the two possible spin orientations of the missing nearest neighbor Mn(II). The large difference in H values observed for Sn(II) and Sn(IV) is interpreted as an indication of the prevalent contribution of 3d-5s transfer in the spin polarization of the diamagnetic impurity. The Mossbauer lattice temperature for the Sn(IV) probe (Θ M = 240 K) is found to be slightly higher than for the Sn(II) one (Θ M = 217 K).

MoS[sub 2] intercalation compounds with transition metals could be of great interest for catalysis of petrochemical processes, and also from the magnetic point of view since, for two-dimensional metallic layers included into a diamagnetic matrix, unusual magnetic properties can be expected. Iron-intercalated molybdenum disulfide, obtained by flocculation of a MoS[sub 2] single-layer dispersion in the presence of ferrous sulfate, was studied by electron microscopy and Moessbauer spectroscopy. Iron was found to occur at both II and III oxidation states between the MoS[sub 2] layers. The formation mechanism of this intercalated compound and its composition are discussed.

Several years old Fe x ZrS 2 samples have been studied again using Mossbauer spectroscopy. As observed just after their preparation, these samples exhibit a double coordinence for iron which is found partly in octaedral partly in tetraedral sulfur surroundings. The striking feature is that the tetraedral population is now more important, due to a migration of iron from the octaedra towards the tetraedra. This effect is attributed to the several years long room temperature annealing which allows the stable state to be approached or reached. For Fe 0.50 TiS 2 , with purely octaedral iron, this migration does not occur.

Intercalation compounds of MoS2 with monomeric or OH-bridged dimeric ruthenium arene cationic complexes have been obtained by interaction of MoS2 single-layer dispersions with aqueous solutions of [(arene)Ru(H2O)3 ]SO4 [arene=C6H6 , C6H2Me4-1,2,4,5, C6H4Me-1-Pri-4]. The structural arrangement of these intercalation compounds is discussed on the basis of XRD and EXAFS data. The arene ligands are orientated roughly perpendicular to the MoS2 slabs. Their nature determines the interlayer spacing as well as the intercalated cation content. Heating removes the organic ligands, while ruthenium-containing species remain in the van der Waals space of MoS2.

We could predict the structure of a new family of compounds Ae(2)F(2)SnX(3) (Ae = Sr, Ba; X = S, Se) from the stacking of known 2D building blocks of the rock salt and fluorite types. With a high-temperature ceramic method we have then succeeded to synthesize the four compounds Ba(2)F(2)SnS(3), Ba(2)F(2)SnSe(3), Sr(2)F(2)SnS(3), and Sr(2)F(2)SnSe(3). The structure refinements from X-ray powder diffraction patterns have confirmed the structure predictions and showed their good accuracy. The structure of the four compounds results from the alternated stacking of fluorite [Ae(2)F(2)] (Ae = Sr, Ba) and distorted rock salt [SnX(3)] (X = S, Se) 2D building blocks. As shown by band structure calculations, these blocks behave as a charge reservoir and a charge acceptor, respectively. Sr(2)F(2)SnS(3) and Ba(2)F(2)SnS(3) are transparent with optical gaps of 3.06 and 3.21 eV, respectively. However, an attempt to obtain a transparent conductor by substituting Ba per La in Ba(2)F(2)SnS(3) was unsuccessful.

W x Mo (1− x ) S 2 compounds with both molybdenum and tungsten present in every disulfide layer, i.e., as an intralayer solid solution, can be obtained. Several synthesis routes have been used but all of them do not allow this solid solution, which evidences the decisive role of the nature of the precursor, to be obtained. We never observed formation of a W x Mo (1− x ) S 2 solid solution resulting from stacking of homocationic [WS 2 ] and [MoS 2 ] layers (interlayer solid solution).

The crystallographically ordered Fe x TiSe 2 compounds ( x = 0.25, 0.38, and 0.50) have been investigated as a function of temperature using Mossbauer spectroscopy, susceptibility measurements, and X-ray diffraction. It is found that the coupling between the iron- d localized and the TiSe 2 -band levels decreases as x increases, contrary to what is usually observed for lower iron contents in related disordered materials. For x = 0.50, magnetostriction is evidenced below T N . Besides, the consequences of iron intercalation in TiSe 2 are analyzed from the viewpoint of the crystal dimensionality as deduced from a thermal expansion study.

A general survey of alkali metals intercalation compounds with titanium and zirconium disulfides is given. A model A + x (Ti S 2 x− or A + (Zr S 2 ) x− with an electronic delocalization in the (Ti 2 S 2 ) or (Zr S 2 ) slabs, is suggested according to crystallographic and magnetic studies, N.M.R. measurements, and chemical behaviour. The alkali metal coordination is related to several factors: size of the A + ion, value of the x parameter, strength of the T.S. bonds.

An electron diffraction study has allowed the crystallographic mechanism to be established for the thermally-induced transition from NbS3 to Nb1.12S2, which belongs to the NbS2 structural type. For the trisulfide, the structural unit is a bicapped trigonal prism [NbS(6+2)] (6 is for the prism, 2 is for the bicapping sulfur atoms). When heating NbS3 one sulfur is removed from every (S2) pair which leads to a (4+2)3 sulfur coordination for niobium. Atomic rearrangements are then needed for new [NbS6] prisms to be reconstructed, perpendicular to the original bicapped ones, and for the NbS2 structural type to establish. The Van der Waals gap orientation remains unchanged through the transition ; no strong bond is unnecessarily broken. The obtained disulfide is not stoichiometric (Nb1.12S2) due to the thermodynamic route followed.