Biomedical subjects

Claude Delmas

Publications and source records attributed to Claude Delmas.

5 recordsLinked to original sources

PubMed2005

First experimental evidence of potassium ordering in layered k4co7o14.

The layered P2-K4Co7O14 oxide has been prepared and characterized by means of X-ray diffraction, electrical conductivity, thermopower, and magnetic measurements. The crystal structure of K4Co7O14 (P6(3)/m space group, Z=2, a=7.5171(1) A, and c=12.371(1) A) consists of a stacking of slabs of edge-shared CoO6 octahedra with K+ ions occupying ordered positions in the interslab space, leading to a a0 radical7xa0 radical7 supercell. Potential energy calculations at 0 K are in good agreement with the ordered distribution of potassium ions in the (ab) plane. This oxide is metallic, and the magnetic susceptibility is of Pauli-type, which contrasts with the Curie-Weiss behavior of the homologous NaxCoO2 (x approximately 0.6) oxide with close alkali content. The thermopower at room temperature is about one-third that of polycrystalline Na0.6CoO2.

Journal Article↗

PubMed2005

6/7Li NMR study of the Li1-zNi1+zO2 phases.

A series of Li1-zNi1+zO2 materials have been synthesised by the coprecipitation route. An X-ray diffraction study was carried out on these materials using the Rietveld method to determine the departure from the ideal stoichiometry z, which ranges from 0 to 0.138. The actual Li/Ni ratio was also checked by chemical analyses using inductively coupled plasma (ICP) for each sample. The stoichiometric sample (z approximately 0) was obtained using a 15% Li excess. (6/7)Li NMR results from LiNiO2 (z approximately 0) show that the asymmetric shape of the NMR signal is due to anisotropy. Calculations give evidence that the paramagnetic dipolar interaction from the electron spins carried by Ni is anisotropic but does not completely explain the experimental anisotropy. (6)Li MAS NMR (magic angle spinning NMR) experiments and temperature standardisation NMR measurements unambiguously assign the isotropic position at +726 ppm. The static-echo NMR spectra of the non-stoichiometric Li1-zNi1+zO2 phases also exhibit an asymmetric shape whose width increases with the departure from the ideal stoichiometry z. (6/7)Li static and MAS NMR show that the 2zNi(2+) ions thus formed modify the dipolar interaction within the materials and also affect the Fermi contact interaction, since a distribution of Li environments is observed using (6)Li NMR for non-stoichiometric samples.

Isotopes↗

PubMed2004

NaRuO2 and NaxRuO2.yH2O: new oxide and oxyhydrate with two dimensional RuO2 layers.

The new oxide and oxyhydrate NaRuO2 and NaxRuO2.yH2O (x = 0.22, y = 0.45) have been characterized. NaRuO2 is isostructural with alpha-NaFeO2. The symmetry is rhombohedral (R3m space group) with lattice parameters of a = 3.018(2) A and c = 16.493(3) A. The structure has been refined by the Rietveld method. The oxyhydrate NaxRuO2.yH2O has been prepared by stirring a sample of NaRuO2 in water at ambient temperature. NaxRuO2.yH2O crystallizes in the space group R3m with lattice parameters of a = 2.930(2) A and c = 21.913(5) A. The structure is related to the CuFeO2 3R polytype structure with the AABBCC sequence of the oxygen close packed layers along the c-axis. Analogies with the related cobalt phases are discussed. The susceptibilities of NaRuO2 and NaxRuO2.yH2O are small and constant in a large temperature range.

Journal Article↗

PubMed2003

59Co, 23Na NMR and electric field gradient calculations in the layered cobalt oxides NaCoO2 and HCoO2.

59Co and 23Na NMR has been applied to the layered cobalt oxides NaCoO(2) and HCoO(2) at three different magnetic field strengths (4.7, 7.1 and 11.7T). The 59Co and 23Na quadrupole and anisotropic shift tensors have been determined by iterative fitting of the NMR line shapes at the three magnetic field strengths. Due to the large 59Co quadrupole interaction in NaCoO(2), a frequency-swept irradiation procedure was used to alleviate the limited bandwidth of the excitation. While the 59Co and 23Na shift and quadrupole coupling tensors in NaCoO(2) are found to be coincident and axially symmetric in agreement with the crystal symmetry requirements, the fits of the 59Co NMR spectra clearly show the presence of structural disorder in HCoO(2). The 23Na chemical shift anisotropy can be reproduced by shift tensor calculations using a point dipole model and considering that the magnetic susceptibility in NaCoO(2) is due to Van Vleck paramagnetism for Co(3+). Electric field gradient calculations using either the empirical point charge model or the ab initio full potential-linearized augmented plane wave method are compared with the experimental NMR data.

Cobalt↗

PubMed2003

Atomic resolution of lithium ions in LiCoO2.

LiCoO2 is the most common lithium storage material for lithium rechargeable batteries, used widely to power portable electronic devices such as laptop computers. Operation of lithium rechargeable batteries is dependent on reversible lithium insertion and extraction processes into and from the host materials of lithium storage. Ordering of lithium and vacancies has a profound effect on the physical properties of the host materials and the electrochemical performance of lithium batteries. However, probing lithium ions has been difficult when using traditional X-ray and neutron powder diffraction techniques due to lithium's relatively low scattering power when compared with those of oxygen and transition metals. In the work presented here, we have succeeded in simultaneously resolving columns of cobalt, oxygen and lithium atoms in layered LiCoO2 battery material, using experimental focal series of LiCoO2 images obtained at sub-ångstrom resolution in a mid-voltage transmission electron microscope. Lithium atoms are the smallest and lightest metal atoms, and scatter electrons only very weakly. We believe our observations of lithium to be the first by electron microscopy, and that they show promise for direct visualization of the ordering of lithium and vacancies in transition metal oxides.

Lithium↗