P. Gressier

Characterization of the new series of quasi one-dimensional compounds(MX4)nY (M =Nb, Ta; X =S, Se; Y =Br, I)

Abstract A detailed investigation on the new series of compounds(MX4)nY (M =Nb, Ta; X =S, Se; Y =Br, I)is given through structural information and resistivity measurements. All these compounds are built with the same framework which is composed ofMX4chains and halogen atoms between these chains. It is found that the resistivity behavior is closely related to the metal-metal sequence along theMX4chain.

Structural determination of a new one-dimensional niobium chalcogenide : FeNb3Se10

Abstract FeNb 3 Se 10 is obtained by heating the elements at 650°C in silica evacuated tubes. The unit cell dimensions are : a = 9.213(1) A ; b= 3.482(1) A ; c = 10.292(1) A ; β = 114.46(4)° The structural determination on a single crystal shows the pseudo 1D-character of the compound. Two types of chains are running in the structure along the b axis. One of them corresponds to a trigonal prismatic frame of selenium, the other develops an octahedral distribution of selenium atoms. Iron is octahedrally coordinated whereas niobium presents both types of environment. The trigonal prismatic chains corresponds exactly to one of the conducting [NbSe 3 ] chains of niobium triselenide. FeNb 3 Se 10 is metallic at room temperature; it undergoes a metal-insulator transition below 140K.

Preparation and structure of (NbSe4)3.33 I. [I3Nb10Se40]

The structural determination of a novel linear chain compound (NbSe4)3.33 I is reported. The structure was solved by means of Patterson and Fourier syntheses and refined toR = 0.030, RW = 0.040, for 566 independent reflexions [I ≥ 3σ (I)]. The structure is built up of infinite [NbSe4] chains along the c axis (tetragonal symmetry). Iodine atoms are located within the channels between these chains. The iodine atoms do not show the same distribution within all the channels as is the case for related compounds such as (NbSe4)3I, (TaSe4)2I. This new compound undergoes a phase transition at 285 K associated with a change density wave (CDW) origin.

A DFT study of lithium battery materials: application to the β-VOXO4 systems (X = P, As, S)

Abstract VO X O 4 systems have been considered as potential lithium battery electrodes. They mainly present two distinct structural types: the tetragonal “ α ” type with a two-dimensional framework, and the three-dimensional orthorhombic “ β ”. DFT calculations were performed on this latter system for several β -Li x VO X O 4 compounds ( x =0, 1; X =P, As, S). They allowed to propose structural models for VOAsO 4 and LiVOSO 4 , not fully crystallographically well described yet. Based on an experimental model of two-phase processes, these calculations led also to a good simulation of electrochemical potential values. A density of states analysis put in evidence the “inductive effect” and the role played by ( X O 4 ) n − groups inside the host frameworks on these potentials.

Synergetic theoretical and experimental structure determination of nanocrystalline materials: study of LiMoS2

A combined approach is proposed to solve the structure of badly crystallized materials. It couples poor quality powder X-ray diagram (XRD) and XRD simulation deduced from first-principle geometry optimization. It is used to completely solve the LiMoS2 structure.

Structural determination and transport properties of a new phase with approximate composition Sn1.2Ti0.8S3

Abstract A new compound Sn 1.2 Ti 0.8 S 3 has been characterized. The unit cell is orthorhombic, space group Pnma, a = 8.899(4) A , b = 3.605(2) A , c = 13.506(6) A . Its crystal structure has been determined and yielded to reliability R factor of 0.025. This structure is reminiscent of that of Sn 2 S 3 where part of Sn IV has been substituted with Ti. The band gap determined from electrical conductivity is found to be 0.05 eV.

The design of new low-dimensional solids

Abstract There is an ever increasing number of diverse phenomena to be found in low-dimensional solids. There is consequently a need for new materials to support new experiments or growing theories. Unfortunately the synthesis of low-dimensional solids is based on a difficult chemistry that must take into account many factors at the same time, some of them being largely conflicting. After a few general considerations on the relationship between electronic structure and structural arrangements and stoichiometries in layered or one-dimensional compounds, this paper will emphasize different approaches to design low-dimensional solids. They are based on examples and concern the role of the ionicity of bonds, the search of polytypes, the stabilization of chains by counter ions or other chains, the preparation of new materials for intercalation chemistry.

Misfit layer compounds family (MS) n TS2 (M = Sn, Pb, Bi, rare earth element; T = Nb, Ta; n = 1.08–1.19)

Abstract Compounds (MS) n TS2, where M is a rare earth element, tin, lead or bismuth and T is a transition metal, constitute a new family of incommensurate materials. They are built up from a succession of |MS| and |TS2| slabs. Each |MS| slab is a distorted NaCl type double layer, where M surrounding is a distorted square pyramid of S atoms. T coordination is trigonal prismatic in |TS2| sandwich, which is very similar to those of 2H-TS2 structures. X-ray diffraction of each type of slab shows that one intralayer lattice parameter of |MS| slab is incommensurate with the corresponding one of a |TS2| slab. Both layers are then commensurate along the stacking axis and one perpendicular direction, and misfitted in any other direction. This misfit is directly responsible for the formulation, e.g. (LaS)1.14NbS2 or (SnS)1.18NbS2. As is shown for (LaS)1.14NbS2, three different approaches were used for the structural determination of these compounds by X-ray diffraction: composite approach, which separates both sub...

A Unique Tool to Study the Intercalation Process

Abstract We applied X-ray Absorption Spectroscopy, in combination with electronic band structure calculations, to probe the electronic structure before and after lithium intercalation into TiS2, TiSe2 and 2H-NbSe2. We are then able to precisely determine the nature of the charge transfer from intercalated lithium to the host It is shown that lithium is not fully ionized and that chalcogen atoms are deeply involved in the charge transfer process.