Caractérisation d'un transect de sols de la station agronomique de Misamfu (Zambie)

Cet article décrit en détail, le long d'un transect de 485 m. situé sur la zone du plateau de la station de recherche de Misamfu, les variations concernant les sols, les horizons indurés associés, la végétation et les termitières. Les auteurs discutent les contraintes physiques des sols pour l'agriculture et, plus particulièrement, la présence et la formation de deux types de croûtes superficielles

CaCu3Ti4O12 ceramics from co-precipitation method: Dielectric properties of pellets and thick films

Dielectric properties of CaCu3Ti4O12 (CCTO)-based ceramics and thick films (e ∼50m) prepared from powders synthesized by a soft chemistry method (co-precipitation) are presented and discussed. The characteristics of pellets and thick films are compared. The pellets exhibit high values of the dielectric permittivity (εr ∼1.4×105) and relatively small dielectric losses (tan δ ∼0.16) at 1 kHz and room temperature. These properties are independent of the nature of the metallization of the electrodes. In addition, the dielectric permittivity decreases when the diameter of the electrodes of the pellets increases, while the losses remain constant. This result, which is strongly related to the nature of the dielectric material in between the electrodes, constitutes a strong indication that the high dielectric permittivity values observed in this material are not related to an interfacial (electrode material) related mechanism but is an internal barrier layer capacitor (IBLC) type. Very high values of the dielectric permittivity of CCTO thick films are measured (εr ∼5×104). The differences in dielectric permittivity between thick films and dense pellets may be attributed to the difference in grain size due to different CuO contents, and to the different reactivity of the materials

Les systèmes transformants d'une couverture ferrallitique de Guyane française : analyse structurale d'une formation supergène et mode de représentation

Les auteurs présentent une étude détaillée d'un interfluve de Guyane française qui apporte une contribution à la connaissance des systèmes transformants dans les formations supergènes des régions tropicales humides