Paul Hagenmuller

Structural classification and properties of the layered oxides

Layer oxides with formula AxMO2 where M stands for a transition element with two oxidation states or for a mixture of tetravalent and trivalent (or eventually divalent) elements are obtained for 0.5 ≤ x ≤ 1. The lattice is built up by sheets of edge sharing MO6 octahedra between which the alkali ions are inserted with trigonal prismatic or octahedral environment. Similar structures can be found among A2MO3 oxides, the alkali ions lying between (A13M23)O2 sheets. The influence of the pressure on the stability of the various packings is discussed. Layer structures are also obtained for the compositions Li8MO6, Li7L□O6 and Li6In2□O6. Structures of these pseudo-2D materials are characterized by a packing of octahedral and tetrahedral sheets where the alkali ions and the vacancies are distributed. Transport properties of these materials have been studied.

Electrochemical intercalation of sodium in naxcoo2 bronzes

The chemical study of the NaxCoO2 system (0.5⩽x⩽1) has shown previously the existence of bronze-type phases with layer structure. In each material the lattice is built up by sheets of edge-sharing CoO6 octahedra allowing Na+ ions to be intercalated with trigonal prismatic surrounding (AABBCC or AABB oxygen packing) for small values of x and octahedral environment (ABCABC oxygen packing) for larger ones. As these materials are mixed conductors, they have been used as cathodes in Na batteries at room temperature. Discharge potentials (2.0<V<3.5V) have been measured as a function of the composition. The electrochemical intercalation of sodium in all these materials is reversible within their existence range. During the electrochemical intercalation a reversible charge is observed between phases having AABBCC and ABCABC oxygen packing. This can be explained by the relatively small displacement of the sheets. In contrast, for the material with AABB oxygen packing no transition occurs since a packing change requires breaking of cobalt-oxygen bonds, which is apparently impossible at room temperature.

Clathrate Structure of Silicon Na8Si46 and NaxSi136 (x < 11).

The crystal structure of two new cubic phases in the silicon-sodium system have been solved from their x-ray diffraction patterns. Both structures are of the clathrate type found for gas hydrates, consisting of tetrahedral networks which are combinations of pentagonal dodecahedra with 14-face polyhedra in one case and with 16-face polyhedra in the other case. There is strict correspondence between the silicon positions and the oxygen positions of the hydrate structures. For one compound, Na8Si46, the centers of all polyhedra are occupied by sodium atoms. For the other compound, there occurs only partial occupancy of the polyhedral cages.

Sur quelques nouvelles phases de formule NaxMnO2 (x ⩽ 1)

Abstract Several new ternary oxides have been isolated in the manganese-oxygen-sodium system for Na Mn ⩽ 1 : Na0.20MnO2, Na0.40MnO2, Na0.44MnO2, Na0.70MnO2+y (0 ⩽ y ⩽ 0.25) and NaMnO2, both with two allotropic varieties. All structures are characterized by edge sharing (MnO6) octahedra, forming double or triple chains for small sodium content and bidimensional layers when the Na Mn ratio becomes close to 1. Electrical and magnetic behaviour of the phases has been determined.

Sur de nouveaux bronzes oxygénés de formule NaχCoO2 (χ1). Le système cobalt-oxygène-sodium

An investigation of the sodium-cobalt-oxygen system allows the isolation of four new bronze type phases with the formula Naχ.CoO2 (χ 1). The structure consists of sheets of octahedra (CoO2)n between which are inserted the sodium ions. Their structures differ from one another by the stacking sequence of the oxygen layers, and by the distortions introduced as a result of the ordering of vacancies among the sodium layers. For phases containing high sodium content, the coordination of the sodium is octahedral; for phases containing smaller amounts of sodium, the coordination becomes trigonal-prismatic.

Sur une nouvelle famille de clathrates minéraux isotypes des hydrates de gaz et de liquides. Interprétation des résultats obtenus

Abstract The thermal degradation of the alkali silicides and germanides of formula MeSi and MeGe (Me = Na, K, Rb, Cs) leads to intermediate phases having the clathrate structure of the gas and liquid hydrates. The alkali atoms occupy holes in a distorted silicon or germanium lattice; a radius intermediate between the ionic and metallic radii accounts for the experimental results, involving a certain localization of the peripheral s electron. This conclusion is confirmed by the magnetic and electric properties.

Sur deux nouvelles phases oxygenees du cuivre trivalent: LaCuO3 et La2Li0, 50Cu0, 50O4

Resume Two new copper III + compounds have been prepared under oxygen pressure and investigated. The first phase LaCuO3 has a distorded rhomboedral perovskite structure ( a = 5.431 ± 0.002 A ; α = 60°51′ ± 0°02′) and the second phase La2Li0.50Cu0.50O4 has the K2NiF4 structure ( a = 3.731 ± 0.002 A ; c = 13.20 ± 0.02 A ). Whereas LaCuO3 shows metallic behaviour, La2Li0.50Cu0.50O4 is diamagnetic and the properties suggest a low spin d8 state for the Cu3+.

Amelioration des conditions de synthese de l'hydrure de magnesium a l'aide d'adjuvants

Addition of metals or alloys whose hydrides have a high dissociation tension allows a considerable increase of the hydrogenation rate of magnesium. The influence of the nature of the adjuvant and its specific concentration, of temperature and hydrogen pressure on the reaction rate, have been carefully studied. The pressure-composition isotherms have been determined especially when the adjuvant is LaNi5.

Preparation and ionic conductivity of new B2S3-Li2S-LiI glasses

Glasses obtained in the B2S3-Li2S-LiI system have been investigated. Ionic conductivity is higher than 10−3Ω−1cm−1 at 25°C for LiI-rich glasses. The electrochemical stability range and chemical stability allow their use as solid electrolytes in solid state batteries.

A nasicon-type phase as intercalation electrode: NaTi2(PO4)3

Abstract Reversible intercalation of sodium in NaTi 2 (PO 4 ) 3 at room temperature can be achieved either chemically or electrochemically. Na 3 Ti 2 (PO 4 ) 3 is obtained as final product via a two phase mechanism. The non-existence between both extreme compounds of a Na 1+x Ti 2 (PO 4 ) 3 solid solution seems to result from a topotactic demixtion reaction which requires only Na + and e − transfers without skeleton bond breaking and recombination.