Jean-Pierre Bonnet

Influence de la pression partielle d'oxygene sur la nature des defauts ponctuels dans Ca2LaFe3O8+x

Abstract The type of point defects in non-stoichiometric Ca2LaFe3O8+x ferrite has been studied by measuring the variation of electrical conductivity with oxygen partial pressure at various temperatures. Several ordering possibilities occur. The oxygen atoms inserted, mostly 1-charged, have a strong tendency to couple at sufficient oxygen pressure and at low temperature. Interstitial oxygen atoms in the lattice vacancies induce structural evolution as non-stoichiometry becomes significant enough.

Etude par mesures electriques des correlations entre defauts de structure et potentiel chimique de l'oxygene dans WO3 non-stoechiometrique

Abstract The variation of the electrical resistivity of non-stoichiometric WO 3 , as a function of oxygen pressure has been studied at 750°C and in the range of 1 atm ⩾ P O 2 ⩾ 10 −16.6 atm, corresponding to 0 ⩽ x ⩽ 0.04. The stair-like log 10 ρ vs log 10 P O 2 curve shows evidence of the existence of seven Magneli type phases in which the conduction mechanism depends on the shear planes rather than on point defects.

Correlations entre la conductivite ionique et la concentration en ions alcalins dans les borates de lithium vitreux

Abstract The electrical transport properties of the B 2 O 3 - xLi 2 O glasses have been investigated. An electrochemical approach allows to give an interpretation of the conductivity based on the carrier concentration in relation with Li 2 O content. The mobility of the Li + ions does not seem to depend on the composition.

The influence of sintering on the electrical conductivity of the Zn0.99Co0.01O solid solution

Abstract The electrical properties of a phase of composition close to Zn 0.99 Co 0.01 O have been studied on pellets sintered at 1300°C under a pure oxygen stream for various periods of time. Plotting of electrical conductivity vs. temperature shows two domains characterized by two different activation energies. The high temperature activation energy depends on sintering time. The authors suggest that this property could be due to non-statistical distribution of cobalt and evaporation of zinc oxide.

Anisotropy in the electrical properties of zirconium doped α -Fe2O3 single crystals

The electrical properties of zirconium doped α -Fe2O3 single crystals have been investigated from 470 up to 1300 K. n nAs for the pure crystal, an anisotropy appears for the conductivity between the [001] direction and the (001) plane, although lowered by the dopant. n nCombining the results of electrical conductivity, thermoelectric power and complex impedance measurements, it was established that there was no significant kinetic contribution of the electrons and that their mobility was lower than a few tenths of cm2V−1s−1.

Existence and role of an amorphous layer at the grain surfaces of YBa2Cu3O7 − δ ceramics obtained by solid state sintering

This paper is dealing with YBa2Cu3O7 − δ ceramics obtained by solid state sintering (TS ≤ 920 °C). The presence of carbonates in the starting powder or the existence of carbon dioxide traces in the gas phase during the heat treatment leads to the formation of a thin amorphous layer at solid-gas interfaces which has been observed by TEM. That layer acts as an oxygen diffusion barrier. Therefore, the reoxidation of the ceramics at low temperature is inhibited, explaining for a part the low values of Jc measured in bulk ceramics. The influence of fluorination treatments is also investigated.

Anisotropy of Electrical Properties in Pure and Doped αFe2O3

The electrical conductivity and the thermoelectric power of pure and nickel-doped α Fe203, studied in the crystallographic plane (001) and along the [001] axis have shown typical anisotropic behaviour.