M. E. Melo Jorge

Effects of synthesis method on stoichiometry, structure and electrical conductivity of CaMnO3−δ

Abstract CaMnO3−δ perovskite samples were synthesised by two different methods: conventional solid-state reaction and the citrate route involving autoignition. The formation of a perovskite phase was significantly influenced by the synthesis and processing conditions: samples obtained by the citrate route have a less distorted structure. These materials are always more oxidised than those prepared by the ceramic route and consequently have a higher Mn+ content. Moreover, they present the highest electrical conductivity values, which is explained by a less distorted structure.

Electron doping of Ca4Mn3O10 induced by vanadium substitution

In this work, electron doping of the anisotropic phase Ca4Mn3O10 was achieved by substitution of manganese by vanadium. No significant structural modifications were detected to the highest substitution ratio of 10% achieved. The introduction of vanadium decreases the electrical resistivity, described as two-dimensional variable range hopping, and induces the appearance of a ferromagnetic behavior. Consistently negative magnetoresistance develops in the magnetic ordered state. These results are characteristic of the presence of double exchange interactions, indicating that vanadium doping induces mixed valence of manganese.

Synthesis and characterisation of CaMn1−xCrxO3−δ phases

Abstract The study of the perovskite manganites CaMn 1− x Cr x O 3− δ had been carried out. These Cr-doped manganites were prepared to study the influence of Mn substitution on the electronic properties. In this paper, we report the results of synthesis and characterisation of these samples. A single phase has been obtained up to x ≤0.20 and the lattice parameters show a linear dependence with Cr content. The XPS and XAS had been performed to get information about the oxidation states of Mn and Cr ions.

Photocatalytic Degradation of Rhodamine 6G using TiO2/WO3 Bilayered Films Produced by Reactive Sputtering

TiO2/WO3 and WO3/TiO2 bilayered films were deposited onto glass substrates by DC reactive magnetron sputtering and their photocatalytic activity was evaluated on the decolorization of Rhodamine 6G (Rh6G) aqueous solutions. The structures, morphologies and optical properties of TiO2 and WO3 layers and also of the bilayered films were studied by X-ray diffraction, field emission scanning electron microscopy and UVVis spectroscopy. It was found that the bilayered films exhibit good adherence to the substrates and high mechanic stability. The structural characterization revealed that in both nanocomposites independently of the above layer, the main phase observed in the X-ray patterns corresponds to WO3 and the optical properties are similar to the WO3 layer. The photocatalytic efficiency of the nanocrystalline bilayered films was further compared with TiO2 and WO3 films also produced by sputtering and the results show that the higher photocatalytic activity was achieved by the bilayered film with WO3 as the upper layer.

Internal Expansive Reactions in Concrete - Prevention of its Occurrence

This work concerns with the study of coatings to inhibit the ingress of water and also the use of lithium nitrate to modify the swelling properties of the ASR reaction products. In order to accomplish these objectives concrete samples extracted from a Portuguese structure affected by internal expansive reactions were treated with six different coatings and subjected to natural and accelerated environments. In order to study the modifications produced by lithium nitrate in the expansive properties of ASR products, different test conditions were used namely the application of lithium by immersion and electrical migration. In this work we present the results of the application of these treatments namely by the evaluation of the mechanical, physical, microstructural and electrical properties.

Electron Doping of Ca4Mn3O10Induced by Vanadium Substitution

In this work, electron doping of the anisotropic phase Ca4Mn3O10 was achieved by substitution of manganese by vanadium. No significant structural modifications were detected to the highest substitution ratio of 10% achieved. The introduction of vanadium decreases the electrical resistivity, described as two-dimensional variable range hopping, and induces the appearance of a ferromagnetic behavior. Consistently negative magnetoresistance develops in the magnetic ordered state. These results are characteristic of the presence of double exchange interactions, indicating that vanadium doping induces mixed valence of manganese.

Electron Doping of Ca 4 Mn 3 O 10 Induced by Vanadium Substitution

In this work, electron doping of the anisotropic phase Ca4Mn3O10 was achieved by substitution of manganese by vanadium. No significant structural modifications were detected to the highest substitution ratio of 10% achieved. The introduction of vanadium decreases the electrical resistivity, described as two-dimensional variable range hopping, and induces the appearance of a ferromagnetic behavior. Consistently negative magnetoresistance develops in the magnetic ordered state. These results are characteristic of the presence of double exchange interactions, indicating that vanadium doping induces mixed valence of manganese.