Extreme in-plane upper critical magnetic fields $B_{c2//ab}$ strongly violating the Pauli paramagnetic limit have been observed in the misfit layer $(LaSe)_{1.14}(NbSe_2)$ and $(LaSe)_{1.14}(NbSe_2)_2$ single crystals with $T_c$ = 1.23 K and 5.7 K, respectively. The crystals show a two-dimensional to three-dimensional transition at temperatures slightly below $T_c$ with an upturn in the temperature dependence of $B_{c2//ab}$, a temperature dependent huge superconducting anisotropy and a cusplike behavior of the angular dependence of $B_{c2}$. Both misfits are characterized by a strong charge transfer from LaSe to $NbSe_2$. As shown in our previous work, $(LaSe)_{1.14}(NbSe_2)$ is electronically equivalent to the highly doped $NbSe_2$ monolayers. Then, the strong upper critical field can be attributed to the Ising coupling recently discovered in atomically thin transition metal dichalcogenides with strong spin-orbit coupling and a lack of inversion symmetry. A very similar behavior is found in $(LaSe)_{1.14}(NbSe_2)_2$, where the charge transfer is nominally twice as big, which could eventually lead to complete filling of the $NbSe_2$ conduction band and opening superconductivity in LaSe. Whatever the particular superconducting mechanism would be, a common denominator in both misfits is that they behave as a stack of almost decoupled superconducting atomic layers, proving that Ising superconductivity can also exist in bulk materials.

On the basis of crystal structures and electronic properties, a critical discussion of the nature of chemical bonds in misfit layered chalcogenides is given. It concerns also the various mechanisms of non-stoichiometry that are present in these incommensurate structures. Misfit chalcogenides with a LnY slab opposed to TY2 ones (T = Ti, V, Cr, Nb, Ta) appear as infinite two-dimensional intercalation compounds with an electron donation from LnY to TY2. In case of PbY or SnY slabs a more complex mechanism involving coupled substitutions in both slabs seems to prevail.

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The new chloro-sulfosalt Pb3+xSb3-xS7-xC1+x. (x similar to 0.45) has been synthesized at 500 degrees C from a mixture of PbS, PbCl2 and Sb2S3. It , crystallizes in the orthorhombic system (space group Pbam), with a = 15.194(3) angstrom, b = 23.035(5) angstrom, c = 4.0591(8) angstrom, V = 1420.6 Z = 4. The crystal structure has been solved by X-ray single-crystal study, with a final R = 0.0497. Deviation from stoichiometric Pb3Sb3S7Cl (x coefficient) follows the substitution rule Sb3+ + S2- -> Pb2+ +Cl-. Sb and Ph sub-positions within mixed (Sb,Pb) sites are discussed; Pb excess precludes any superstructure along c. A unique'pure Cl position is bound only to Pb atoms with a distorted square coordination. The title compound is a rod-type structure derived from the SnS archetype, homeotypic with Pb6Sb6S14(S-3), where the (S3)(2-) trimer is replaced by two Cl-; this substitution is quite isovolumic. Other similar structures are: three polychalcogenides Sr(6)Sb(6)Sl(4)(S-3), Pb6Sb6Se14(Se-3) and EU6Sb6S14(S-3); KLa1.28Bi3.72S8 and its Ln isotypes; dadsonite, Pb23Sb25S60Cl. Pb3+xSb3-xS7-xCl1+x, is the N = 2 member of the homologous series Pb(2 + 2N)(Sb,Pb)((2 + 2N))S(2 + 2N)(S,Cl)((4 + 2N))Cl-N; the N = I member corresponds to the previously known -Pb4.3Sb3.7S8.7Cl2.3 Compound. Other polychalcogenide derivatives of this homologous series are K2Pr2-xSb4+xSe8(Se-4) and its Ln isotypes (N = 1), as well as SrBiSe3 (N = 3). Such a comparative modular analysis allowed to propose a structural model for the previous synthetic "Phase Y", similar to Pb10Sb10S23Cl4, corresponding to the combined N = (I + 2) homolog. (C) 2008 Elsevier Inc. All rights reserved.

The structures of the new oxysulfide Ruddlesden-Popper phases La2LnMS2O5 (Ln=La, Y; M=Nb, Ta) are reported together with an iodide-containing variant: La3-xNb1+xS2O5I2x (0<or=x<0.11). Structures were refined against powder-neutron or single-crystal X-ray diffraction data. All of these compounds exhibit an intergrowth structure with NaCl-type slabs [La2S2] alternating regularly with perovskite-type oxide slabs [LnMO5] or [La1-xNb1+xO5I2x]. In the oxide slabs, the trivalent and pentavalent cations are disordered on the long-length scale probed by diffraction methods, but bond length considerations suggest that they must be ordered at least on the length scale of the unit cell. The [LnMO5] block of the iodide-free compounds derive from the ideal [Ti2O5] blocks found in Ln2Ti2S2O5 (Ln=Nd-Er; Y) by the formal substitution of two Ti4+ ions with one Ln3+ and one M5+ion. The unusual partial insertion of iodide in the perovskite voids of the [LaNbO5] block in La3NbS2O5 was found to be coupled to a La/Nb substitution, maintaining the charge balance within the [La1-xNb1+xO5I2x]2- block. The Nb5+ ions were found to be too resistant to reduction to undergo the intercalation of alkali metals observed in the Ln2Ti2S2O5 series.

Interlayer magnetotransport measurements on the highly anisotropic (LaSe)1.14(NbSe2) superconductor with Tc∼1.2K have indicated that this layered compound represents a model system of intrinsic Josephson junctions [P. Szabó et al., Phys. Rev. Lett. 86 (2001) 5990]. Scanning tunneling microscopy at room temperature and tunneling spectroscopy measurements at very low temperatures are presented in this work. STM imaging has revealed the presence of two types of surfaces which can be attributed to the appearance of LaSe or NbSe2 layers on the surface. The use of STM tip made of superconducting lead enabled a precise measurement of the temperature dependence of the superconducting energy gap Δ(T) on the NbSe2 layer. Δ(T) obtained from the surface sensitive STS data support the scenario obtained from our previous interlayer – ergo bulk sensitive magnetotransport measurements.

The new oxy-chloro-sulfide (Mn1-xPbx)Pb10+ySb12-yS26-yCl4+yO (x is an element of [0.2-0.3]; y is an element of [0.3-1.6]) was synthesized by dry way at 500-600 degrees C. A single crystal similar to Mn0.7Pb11.0Sb11.3S25.3Cl4.7O indicates a rnonoclinic symmetry, space group C2/m, with a = 37.480(8), b = 4.1178(8), c = 18.167(4) angstrom, beta = 106.37(3)degrees, V = 2690.2(9) angstrom(3), Z = 2. Its crystal structure was determined by X-ray single crystal diffraction, with a final R = 5.11%. Modular analysis of the crystal structure reveals a "waffle" architecture, where complex rods with lozenge section delimitate an internal channel filled by a single chain of (Mn0.7Pb0.3)Cl-6 octahedra connected by opposite edges. Minimal inter-chain distances are close to 18 A. The rod wall, two-atom thick, presents, in alternation with S atoms, Pb or (Pb,Sb) cations with prismatic coordination in the internal atom layer, while the external atom layer is constituted exclusively by Sb cations with dissymmetric square pyramidal coordination. A (Pb,Sb)(2)S-2 fragment connects two successive rods along (201) to form a waffle-type palissadic layer. The unique O position, half filled, presents the same environment than the isolated O positions in the oxy-sulfide Pb14Sb30S54O5, or oxy-chloro-sulfides Pb18Sb20S46Cl2O and (Cu,Ag)(2)Pb21Sb23S55ClO. This compound belongs to a pseudo-homologous series of chalcogenides with waffle structure, ordered according to the size of their lozenge shape channel. Such a complex senary compound of the oxy-chloro-sulfide type illustrates the structural competition between three cations, on one hand, and, on the other hand, three anions. This compound is of special interest regarding the ID distribution of magnetic Mn2+ atoms at the similar to 2 nm scale. (C) 2007 Elsevier Inc. All rights reserved.

The crystal structure of Pb2SbS2I3 was solved at room temperature and 100 K. At 293 K it crystallizes in the orthorhombic system, space group Cmcm (No. 63), with unit cell parameters a = 4.3262(9), b = 14.181(3), c = 16.556(3) angstrom(3), V = 1017.7(4) angstrom(3), Z = 4. The structure is disordered, and combines a split Pb site (s.o.f. = 0.50) with one mixed (Pb,Sb) site with Pb and Sb in two distinct sub-positions. At 100 K, it is monoclinic, space group P2(1)/c, with unit cell parameters a = 7.3629(6), b = 16.466(3), c = 8.5939(7) angstrom, beta = 107.14(2)degrees, V= 995.6(2) angstrom(3), Z = 4. The structure is now fully ordered, without mixed sites. On the basis of bond valence calculations, new cation distributions are proposed for published structures of the Sn isotypes, Sn2SbS2I3 and Sn2SbSe2I3. A re-examination of the crystal structures of various (Pb/Sn/Sb) chalcogeno-iodides is presented according to modular analysis. All these structures can be described according to three types of ID modules, (Pb/Sn)I-4, (Sn)(2)I-4 and (Pb/Sn/Sb)(4)(S/Se)(2)I-4. Generally each type of ID module gives one type of slab, and the final structure corresponds to a specific stacking of two or three among these slabs. A new structural model is proposed for "alpha-Sn2SI2", which would have the non-stoichiometric composition (Sn-5.42 square(0.58))S-2(I-6.87 square(0.12)), ideally Sn27S10I34 with probably a narrow solid solution field on the SnS-SnI2 joint. (c) 2007 Elsevier Masson SAS. All rights reserved.

Marrucciite, Hg 3 Pb 16 Sb 18 S 46 , is a new sulfosalt discovered in the Fe-Ba deposit of Buca della Vena, Apuan Alps (Italy). It occurs as black acicular metallic crystals in calcite veins; reflectance values in air are (R %, λ nm): 33.1 ( 470 ), 30.0 ( 546 ), 28.8 ( 589 ), 26.5 ( 650 ). Marrucciite is monoclinic, space group C 2/ m , with a 48.32(1) A, b 4.117(1) A, c 24.056(5) A, β 118.84(3)°, V 4192(3) A 3 , Z = 2, D calc. = 6.00 g/cm 3 ; a 2 b superstructure is present. Main lines of the X-ray diffraction powder pattern [d (in A), I (main hkl)]: 4.02, 33 (12.0.3, 802); 3.480, 64 (803, 604); 3.418, 88 (607, 10.0.2, 314) ; 3.106, 31 (9.1.4); 2.994, 100 (11.1.2); 2.922, 41 (11.1.1); 2.056, 52 (020); 1.764, 41 (627). Electron microprobe analysis gave (wt.%; mean of 4 spot analyses): Cu 0.18(12), Hg 7.90(9), Pb 42.41(7), Sb 29.71(7), S 19.47(18), Cl 0.06(2), sum 99.73(14). The chemical formula (basis: 46 (S + Cl) at.) is Cu 0.21 Hg 2.98 Pb 15.46 Sb 18.44 S 45.87 Cl 0.13 , giving the stoichiometric one Hg 3 Pb 16 Sb 18 S 46 that fulfils the charge balance. X-ray single crystal study (R = 9.56 %) revealed a complex structure, with Hg in two specific distorted octahedral coordinations (2 short distances each, close to 2.36 A). There are 40 other independent positions: 7 Pb, 2 (Pb,Sb), 8 Sb and 23 S. The general architecture of the structure is strongly related to that of hexagonal Ba 12 Bi 24 S 48 , with three types of Me 10 S 14 rods (× 2) around a HgSb 2 Pb 4 S 4 central column. It explains the pseudo-hexagonal symmetry ( a /2 ~ c ; β ~ 120°). A strong topologic relationship exists also between marrucciite and scainiite. Like rouxelite, the other coexisting Hg bearing sulfosalt, marrucciite was formed by hydrothermal process during the Apenninic tectono-metamorphic event.

A current switching effect of several orders of magnitude was observed in the incommensurate misfit layered compound ${(\mathrm{La}\mathrm{S})}_{1.196}\mathrm{V}{\mathrm{S}}_{2}$. This effect involves correlated vanadium ${t}_{2g}$ states in a hexagonal $[\mathrm{V}{\mathrm{S}}_{2}]$ layer. Application of moderate electric fields $(\ensuremath{\sim}50\phantom{\rule{0.3em}{0ex}}\mathrm{V}∕\mathrm{cm})$ induces a dielectric breakdown and restores a metallic state. The large pretransitional nonlinearities are consistent with a Poole-Frenkel mechanism which highlights the role of Coulomb interactions. This behavior and the strong modulation of the vanadium atom positions, revealed by single crystal x-ray structure determination, are in favor of a heterogeneous charge distribution. With respect to recent theoretical works, we suggest that the current switching effect observed in ${(\mathrm{La}\mathrm{S})}_{1.196}\mathrm{V}{\mathrm{S}}_{2}$ is related to the breakdown of a remaining Mott insulator state.

The structure of the title compound, NbSeCl3, was determined by single-crystal X-ray diffraction. The structure consists of NbSeCl3 chains centred on the Nb atoms. These chains, with a zigzag development along the c direction, show a regular alternation of short and long Nb—Nb distances. NbSeCl3 is isostructural with NbSeBr3; it may be described as 2(Nb4+) (Se22−) 6(Cl−), with the presence of both (Nb—Nb)8+ and (Se—Se)2− dimers.

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.

RELATIONSHIPC336 calculated in order to describe the effect of the small guest molecules on the crystal structure.Also the influence of the replacement of the phenyl substituent to naphtyl and the exchange of the carbinol C to Si on the inclusion properties and on the geometry of the host molecules has been studied.

Single crystal X-ray diffraction was used to determine the modulated structure of the misfit layer compound (LaS)(1.196)VS2. This compound crystallizes in the triclinic system with cell parameters: a(s) = 3.410 (1) Angstrom, b(s) = 5.845(1) Angstrom, c(s) = 11.191(2) Angstrom, alpha approximate to 95.15(4), beta approximate to 84.79(2)degrees, and y approximate to 89.98(2)degrees, q = 0.5978(4)a(s)* - 0.002(1)b(s)* + 0.004(2)c(s)*, and V-s = 221.2(1) Angstrom(3). A (3 + 1)D superspace group, X (1) over bar(alpha,beta,gamma), was used to analyze the complete structure (X is referring to a pseudo C centering). The largest modulation amplitudes are observed for La-S (between La (subsystem 2) and S (subsystem 1)), as well as V-V distances. In connection with the large V-V modulation, we observed the formation of "linear vanadium clusters" that may impact on the transport properties. (C) 2004 Elsevier Ltd. All rights reserved.

Fe[(CH3(CH2)(2)PO3)(H2O)] (1) and Fe[(CH3(CH2)(17)PO3)(H2O)] (2) were synthesized by reaction of FeCl2 center dot 6H(2)O and the relevant phosphonic acid in water in presence of area and under inert atmosphere. The compounds were characterized by elemental and thermogravimetric analyses, UV-visible and IR spectroscopy. The crystal structure of (1) was determined from X-ray single crystal diffraction studies at room temperature: monoclinic symmetry, space group P2(1), a = 5.707(1) angstrom, b = 4.811(1) angstrom, c = 11.818(2) angstrom, and beta = 98.62(3)degrees. The compound is lamellar and the structure is hybrid, made of alternating inorganic and organic layers along the c direction. The inorganic layers consist of Fe(II) ions octahedrally coordinated by five phosphonate oxygen atoms and one from the water molecule, separated by bi-layers of propyl groups. A preliminary structure characterization of compound (2) suggests a similar layered structure, but with an interlayer spacing of 40.3 angstrom. The magnetic properties of the compounds were both studied by a dc and ac SQUID magnetometer. Fe[(CH3(CH2)(2)PO3)(H2O)] (1) obeys the Curie-Weiss law at temperatures above 50 K (C = 3.81 cm(3) K mol(-1), theta = -62 K), indicating a Fe +II oxidation state, a high-spin d(6) (S = 2) electronic configuration and an antiferromagnetic exchange couplings between the near-neighbouring Fe(II) ions. Below T = 22 K, Fe[(CH3(CH2)(2)PO3)(H2O)] exhibits a weak ferromagnetism. The critical temperature of T-N = 22 K has been determined by ac magnetic susceptibility measurements. Compound (2) shows the same paramagnetic behaviour of the iron (II) propyl derivative. The values of C and theta were found to be 3.8 cm(3) K mol(-1) and -44 K, respectively, thus suggesting the presence of Fe +II ion in the S = 2 spin state and antiferromagnetic interactions between Fe(II) ions at low temperatures. Zero-field and field cooled magnetic susceptibility vs. T plots do not overlap below T = 30 K, suggesting the presence of an ordered magnetic state. The critical temperature, T-N, has been located by the peaks at T-N = 26 K from the ac susceptibility (chi' and chi '') vs. T plots. Below T-N hysteresis loops recorded in the temperature region 16< T <26 K show an S-shape, while below 15 K assume an ellipsoid form. They reveal that compound (2) is a weak ferromagnet. The critical temperature T-N in these layered Fe(II) alkylphosphonates is independent of the distance between the inorganic layers. (C) 2005 Elsevier Inc. All rights reserved.

A new phase in the quinary system La/Ti/Zr/S/O was obtained from a mixture of La2O3, La2S3, ZrO2, and TiO2 by a solid-state reaction at 1273 K in a sealed fused-silica tube. The structure of this new phase, La5Ti similar to 3.25Zr similar to 0.25S5O9.25, was solved by singlecrystal X-ray diffraction, with R-(obs) = 3.37% for 2764 reflections (I > 3 sigma(I)) and 125 variables. This compound crystallizes with four formula units in the monoclinic space group C2/m with lattice constants a = 18.401(2) angstrom, b = 3.9032(3) angstrom, c = 21.944(3) angstrom, and beta = 106.100(8)degrees. The structure can be viewed as a 2D building constituted from two-atom-thick slabs of rock salt type ( = sulfide part) which are interleaved with double-octahedral chains centered on titanium/zirconium atoms (mixed Ti/Zr sites) and drawing a zigzag arrangement ( = oxide part). In addition, EDXS analyses show that a solid solution Ti/Zr exists with a general formulation La(5)Ti(3.5-x)Z(1x)S(5)O(9.25) (where 0. 1 <= x <= 0.5). (c) 2005 Elsevier Inc. All rights reserved.

The design of inorganic compounds is a challenging task in Material Sciences. True examples are still scarce. Using a novel concept of 2D building blocks we were able to predict the compositions and structures of more than 10 new inorganic compounds and to successfully synthesize them.