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First Principles Study of Copper Sulfides (for applications as photoconductors)

J. A. Ferreira; Maria Helena Sousa Soares de Oliveira Braga

The Tetrahedrite’s family constitutes a complete solid-solution series, and is among the most frequent complex sulfides in Nature. This kind of structure can be generically expressed by the composition, Cu12Sb4S13. We have calculated the electronic band structure of Cu12Sb4S13 and Ag6Cu6Sb4S13 (with band gaps of 1.24 and 1.20 eV, respectively) to demonstrate that different elements occupying certain sites...


First Principles Calculations and Experiments to Determine the Hydrogenation Pr...

Maria Helena Sousa Soares de Oliveira Braga; Maria Caçote; J. A. Ferreira; L. L. Daemen

Density Functional Theory (DFT) calculations were performed. They were firstly implemented to optimize the structure and refine the stoichiometry of the only ternary compound, CuLi0.08Mg1.92 of the Cu-Li-Mg system. Furthermore using DFT, several possible structures of CuMg2Hx were optimized. Since most of the hydrides are cubic structures or can be considered as distortions of a cubic structure, we have started...


Neutron Scattering to Characterize Cu/Mg(Li) Destabilized Hydrogen Storage Mate...

Maria Helena Sousa Soares de Oliveira Braga; M. Wolverton; A. Lobet; Luke Daemen


Phase field simulations in miscibility gaps

Maria Helena Sousa Soares de Oliveira Braga; Joana Cassilda Rodrigues Espain de Oliveira; Luís Filipe Malheiros de Freitas Ferreira; J. A. Ferreira

Using phase field simulations, it is possible to simulate the dynamics and morphology of immiscible liquids/solids appearing at the miscibility gap of any system. These simulations may also be used to determine the asymptotic compositions of the fluids for a given Gibbs energy. Even more, it is known that different parameters of the excess Gibbs energy of a certain phase may exhibit different asymptotic morphol...


Thermodynamic assessment of the Bi–Sn–Zn System

J. Vizdal; Maria Helena Sousa Soares de Oliveira Braga; A. Kroupa; K. Richter; Delfim Soares; Luís Filipe Malheiros de Freitas Ferreira; J. Ferreira

A thermodynamic assessment of the Bi–Sn–Zn ternary system was carried out using the CALPHAD approach along with thermodynamic descriptions from new assessments of the Bi–Sn and Bi–Zn systems. Selected experimental data from the literature and our own work were also used. New sets of optimized thermodynamic parameters were obtained that lead to a very good fit between the calculated and e...


A ternary phase in Cu-Li-Mg system

Maria Helena Sousa Soares de Oliveira Braga; J. Ferreira; Luís Filipe Malheiros de Freitas Malheiros

A previous study on Cu–Li–Mg system pointed out the existence of Cu8Li2Mg15, with an orthorhombic structure. The authors of the present paper also detected the existence of a ternary phase similar to the one mentioned. Due to some doubts on the phase’s structure, a study of Cu–Li–Mg was focused in an area near to the composition of that phase. SEM/EDS measurements of the phases&#82...


The behaviour of the lattice parameters in the Bi-Sn-Zn system

Maria Helena Sousa Soares de Oliveira Braga; J. Ferreira; Luís Filipe Malheiros de Freitas Ferreira

Lattice parameters, coefficients of thermal expansion and mass density were determined by means of X-ray powder diffraction between 30 and 180 ºC (or 240 ºC - depending on samples' composition). Rietveld refinement was performed in order to obtain phases' lattice parameters at each temperature. The Panalytical X´Pert Pro MPD was used for room temperature X-ray diffraction experiments (RTXRD) with bulk sam...


HT-XRD in the study of Cu-Li-Mg

Maria Helena Sousa Soares de Oliveira Braga; J. Ferreira; Luís Filipe Malheiros de Freitas Malheiros; Marko Hämäläinen


The experimental study of the Bi-Sn, Bi-Zn and Bi-Sn-Zn systems

Maria Helena Sousa Soares de Oliveira Braga; J. Vizdal; A. Kroupa; Delfim Soares; J. Ferreira; Luís Filipe Malheiros de Freitas Ferreira

The binary BiSn was studied by means of SEM (Scanning Electron Microscopy)/EDS (Energy-Dispersive solid state Spectrometry), DTA(Differential Thermal Analysis)/DSC (Differential Scanning Calorimetry) and RT-XRD (Room Temperature X-Ray Diffraction) in order to clarifydiscrepancies concerning the Bi reported solubility in (Sn). It was found that (Sn) dissolves approximately 10 wt% of Bi at the eutectic temperatur...


CuMg2-yLix alloy for hydrogen storage

Maria Helena Sousa Soares de Oliveira Braga; Luís Filipe Malheiros de F. Ferreira


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    Financiadores do RCAAP

Fundação para a Ciência e a Tecnologia Universidade do Minho   Governo Português Ministério da Educação e Ciência Programa Operacional da Sociedade do Conhecimento União Europeia