Topotactic Reduction and Reoxidation of Hexagonal RCu0.5Ti0.5O3 (R =Y, Eu-Lu) Phases

Hexagonal AMO₂ and AMO₃ phases have the same basic structure, and intermediate compositions for this structure have been prepared by topotactic oxidation of AMO₂ phases such as RCuO₂, where R is a trivalent rare earth cation. We now find that such intermediate phases can also be prepared by topotactic reduction of hexagonal RCu₀.₅Ti₀.₅O₃ (R = Y, Tb-Lu) phases. Our TGA and magnetic susceptibility studies indicate a formula of RCu₀.₅Ti₀.₅O₂.₇₈ for these reduced phases. Topotactic reoxidation occurs on heating these phases to 400°C in air.Keywords: Magnetic properties, Inorganic compounds, Crystal structure, Electronic properties, Chemical synthesi

Sur le "terrain", dans l'Académie de Nantes

Bolo Bernard A., Romian Hélène. Sur le "terrain", dans l'Académie de Nantes. In: Repères pour la rénovation de l'enseignement du français à l'école élémentaire, n°15, 1972. pp. 84-86

Ley grassland under temperate climate had a legacy effect on soil organic matter quantity, biogeochemical signature and microbial activities

Temporary (ley) grassland introduced into cropping cycles has been advocated as being beneficial for the delivery of ecosystem services by agricultural soils. The management of these temporary grasslands has unknown effects on soil organic matter (SOM) concentrations and biogeochemical properties of the cropland soils following the grassland phase. Here, we investigated the legacy effect of differently managed temporary grasslands, i.e. change of soil properties lasting beyond three years of crop. We assessed soil organic carbon (SOC) quantity and SOM biogeochemical signature (composition of soil neutral carbohydrates and lignin), as well as microbial activities (potential C and N mineralization and denitrification). We used a long-term field experiment on Cambisol with temperate climate in western France, where temporary grassland management practices differed in terms of duration (3 or 6 years) and presence or absence of N fertilisation. Topsoil (10 cm) samples were collected after a 3-yr crop rotation (maize, wheat, barley).Our results showed that N fertilisation during the grassland phase was necessary to maintain soil C and N concentrations beyond three years of crop. Temporary grassland management may affect microbial activities as indicated by contrasting polysaccharide and lignin composition. It had however, no effect on potential CO2 and N2O emissions during laboratory incubations. The biogeochemical signature of SOM was close to continuous grassland only in treatments with 6 yrs of fertilized temporary grassland. We thus, conclude that the legacy effects of a grassland phase on SOC quantity and properties of SOM depend on its management

Effet de la gestion des prairies sur le stockage de la matière organique du sol et les émissions de gaz à effet de serre

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