Olivier Amiel

Syntheses, crystal structures and ionic conductivities of orthorhombic Ag2HfS3 and cubic Ag4Hf3S8

Abstract The new compounds, orthorhombic Ag 2 HfS 3 and cubic Ag 4 Hf 3 S 8 , have been prepared by solid state reaction. Their crystal structures and transport properties have been studied using X-ray diffraction, ionic conductivity measurement and the EMF method. The conductivities of silver ion of these compounds reach values around 10 −3 Ω −1 cm −1 at ambient temperatures. The transference numbers of silver ion are found to be close to unity.

Preparation of spherical and controlled size particles of silica or tantalum oxide by chemical reaction in aerosols

Abstract Spherical particles of silica or tantalum oxide were prepared by the hydrolysis of aerosols consisting of silicon tetrachloride or tantalum pentaethoxide, respectively, diluted in propanol-2. Silica particles so-obtained were spherical but agglomerated, and of a rather broad size distribution. However, the particles of tantalum oxide prepared were spherical, non-agglomerated and of narrow size distribution; the mean diameter ranged between 0.84 and 1.72 μm, depending on temperature and the gas flow rate. In both cases the particles were amorphous and crystallized after calcination at high temperature.

Insertion of lithium into Ag4Hf3S8 and Ag2HfS3 by n-BuLi and its structural change

Abstract A study has been made of insertion of lithium into silver hafnium sulfides by soft chemical method using n -butyl lithium. As the starting ternary compounds, orthorhombic Ag 2 HfS 3 (S.G Cmca with a =11.458 A, b =6.628 A and c =12.774 A) and cubic Ag 4 Hf 3 S 8 (S.G P 4 3 32 with a =10.9015 A) synthesized from solid state reaction were chosen. Lithiated products were examined with an X-ray powder diffraction, chemical analyses and conductivity measurements. In both cases polycrystalline new phases were derived together with the occurrence of native silver. Within them only the lithiated Ag 4 Hf 3 S 8 phase could be indexed by a cubic cell with a =10.4327(9) A. Its chemical composition has been determined to be Li 5 Ag 2 Hf 3 S 8 by ICP-AES method. Structure model is discussed on the basis of topochemical replacement reaction. The OCV of Li/Li + /sample measured are 2.5 V for Ag 4 Hf 3 S 8 and 2.1 V for Li 5 Ag 2 Hf 3 S 8 respectively.

Crystal Structure and Properties of Ag7-xTaSe6-xIx (0≤x≤1)

A new argyrodite-type compound Ag7-xTaSe6-xIx (0≤x≤1) has been studied in terms of crystal structure and properties. Depending on x value, two types of cubic phases were obtained: one with S.G. P213 is in the range 0≤x≤0.2 and the other one with S.G. F3m is in the range 0.2≥x≤1. Single crystals were prepared by solid state reaction at 900°C for 2 weeks. Crystal structure analyses were performed with CAD-4 four-circle X-ray method using Mo Kα radiation.

Chemical, structural and microstructural characterizations of Ta 2 O 5 particles derived from an aerosol process

Vapor phase hydrolysis of a liquid tantalum pentaethoxide aerosol gives rise to spherical and nonagglomerated Ta2O5 particles of controlled size and of narrow size distribution. The particles are amorphous and their chemical composition can be expressed as Ta2O5.(nH2O, n′OH, n″OEt). From a microstructural point of view, each particle is constituted of a porous core surrounded by a dense shell with a very smooth surface. After a heat treatment at 850° the sponge-like structure transforms into small crystallites whereas the outer shell converts into juxtaposed monocrystalline domains. Increasing the temperature from 850 to 1250° induces sintering between the crystallites, and large intragranular pores can appear inside the particles. As the temperature increases, the internal porosity is eliminated causing some modifications in particle shape. In particular, the smooth surface of freshly prepared particles is not maintained as shown by the emergence of a markedly granular surface state.