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Centre for Nuclear Sciences and Technologies
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In-Depth Inhomogeneities in CIGS Solar Cells: Identifying Regions for Performance Limitations by PIXE and EBS
Publication . Corregidor, V.; Barreiros, M. Alexandra; Salomé, P.M.P.; Alves, L. C.
ABSTRACT: When considering materials to be used as active layers in solar cells, an important required parameter is the proper knowledge of their elemental composition. It should be heavily controlled during growth in order to obtain the desired band gap and to decrease the recombination defects and then increase the solar cell electrical performance. Ion beam analytical (IBA) techniques and, in particular, particle-induced X-ray emission (PIXE) and elastic backscattering spectrometry (EBS) are quite suitable to determine the thickness and composition of such active layers. Furthermore, if these techniques are performed using a nuclear microprobe, lateral and in-depth inhomogeneities can be clearly observed from 2D maps. In many cases, composition variations can be detected from the classical 2D maps obtained from the PIXE spectra. In this work, it is shown how the in-depth variations can also be studied when considering 2D maps reconstructed from the EBS spectra. Such variations are derived from processing conditions and can be related to (i) composition, (ii) thickness, (iii) roughness, and (iv) other nontrivial issues. Examples obtained on Cu(In,Ga)Se-2-based cells are presented and discussed. Furthermore, the combination of IBA techniques such as PIXE and EBS is shown to be a competitive and alternative method to the more used and established techniques such as X-ray fluorescence for checking the average composition of the solar cell active layers or secondary ion mass spectroscopy for determination of the elemental depth profile.
Hybrid molecular dynamic Monte Carlo simulation and experimental production of a multi-component Cu-Fe-Ni-Mo-W alloy
Publication . Dias, Marta; Almeida Carvalho, Patricia; Gonçalves, António Pereira; Alves, E.; Correia, J.B.
ABSTRACT: High-entropy alloys are a class of materials intensely studied in the last years due to their innovative properties. Their unconventional compositions and chemical structures hold promise for achieving unprecedented combinations of mechanical properties. The Cu-Fe-Ni-Mo-W multicomponent alloy was studied using a combination of simulation and experimental production to test the possibility of formation of a simple solid solution. Therefore, Molecular Dynamics and hybrid Molecular Dynamic/Monte Carlo simulations from 10K up to the melting point of the alloy were analyzed together with the experimental production by arc furnace and powder milling. The Molecular Dynamics simulations starting with a bcc type-structure show the formation of a singlephase bcc solid solution type-structure, whereas using Monte Carlo one, generally produced a two-phase mixture. Moreover, the lowest potential energy was obtained when starting from a fcc type-structure and using Monte Carlo simulation giving rise to the formation of a bcc Fe-Mo-W phase and a Cu-Ni fcc type-structure. Dendritic and interdendritic phases were observed in the sample produced by arc furnace while the milled powder evidence an separation of two phases Cu-Fe-Ni phase and W-Mo type-structures. Samples produced by both methods show the formation of bcc and a fcc type-structures. Therefore, the Monte Carlo simulation seems to be closer with the experimental results, which points to a two-phase mixture formation for the Cu-Fe-Ni-Mo-W multicomponent system.
Simulation and study of the milling parameters on CuFeTaTiW multicomponent alloy
Publication . Martins, Ricardo; Gonçalves, António Pereira; Correia, J.B.; Galatanu, Andrei; Alves, E.; Dias, Marta
ABSTRACT: The CuFeTaTiW multicomponent alloy has been devised as an interlayer thermal barrier in nuclear fusion re-actors. In order to predict the phase constitution of this alloy, two different lines of work were performed: (a) simulation using Molecular dynamics and Monte Carlo and (b) study of the influence of mechanical alloying parameters on the structures formed. The simulation results show that the most stable structure is achieved starting from a bcc type-structure and using Monte Carlo simulation. In fact, in these conditions the separation into two bcc phases Fe-Ta-W and Cu-Ti is predicted at room temperature. However, the experimental preparation of the materials with mechanical alloying revealed that from 2 h of milling a single bcc phase is formed. The structure of the milled powder was not much influenced by the amount of the process control agent and the by the size of the W starting particles, but generally there was formation of Ta2H from the reaction between the powders and the process control agent.
Thermoelectric Properties of Tetrahedrites Produced from Mixtures of Natural and Synthetic Materials
Publication . Santos, Beatriz; Esperto, Luís; Figueira Vasques, Isabel; Mascarenhas, João; Lopes, E.B.; Salgueiro, Rute; Silva, Teresa; Correia, Jose B.; de Oliveira, Daniel Pipa Soares; Pereira Gonçalves, Antonio; Neves, Filipe
ABSTRACT: Thermoelectric materials have considerable potential in the mitigation of the global energy crisis, through their ability to convert heat into electricity. This study aims to valorize natural resources, and potentially reduce production costs, by incorporating tetrahedrite-tennantite (td) ores from the Portuguese Iberian Pyrite Belt into synthetic samples. The ore samples were collected in a mine waste at Barrig & atilde;o and as "dirty-copper" pockets of ore from the Neves Corvo mine. Subsequently, high-energy ball milling and hot pressing were employed in the production of thermoelectric materials. These are characterized by XRD, SEM/EDS, and thermoelectrical properties. The complete dissolution of the dump material sulfides with the synthetic tetrahedrite constituents led to an increase in the amount of the tetrahedrite-tennantite phase, which was made up of a tetrahedrite-tennantite-(Fe) solid solution. The thermoelectric characterization of these materials is provided, revealing that most of the combined synthetic ore samples displayed better results than the pristine tetrahedrite, mostly due to higher Seebeck coefficient values. Furthermore, the best thermoelectric performance is achieved with 10% of ore, where a power factor of 268 mu W.K-2.m-1 is reached at room temperature.
Novel fast synthesis route for α-MgAgSb thermoelectric materials
Publication . Santos, Beatriz; Sá, Ana; Luz, Paulo P. da; Neves, Filipe; de Boor, Johannes; Pereira Gonçalves, Antonio
ABSTRACT: Thermoelectric (TE) materials capable of waste heat recovery in the temperature range of 300-525 K remain relatively underdeveloped compared to conventional Bi2Te3-based systems, which present inherent environmental, health, and cost challenges. Recently, MgAgSb-based compounds have garnered significant research interest for applications in this temperature range owing to their intrinsically low thermal conductivity, high figure of merit and higher abundance. However, synthesis of the desired low-temperature alpha-MgAgSb phase typically requires highly controlled production processes-such as multi-step mechanical alloying, followed by extensive, week-long annealing-to mitigate the formation of or transition to undesirable phases. This study proposes an original, rapid, and scalable synthesis strategy combining induction melting for only six minutes with the subsequent classic hot-pressing method. We investigated the effect of nominal stoichiometry on thermoelectric performance by synthesising three distinct compositions: MgAg0.97Sb0.995, MgAg0.965Sb0.985, and MgAg0.955Sb0.985. The MgAg0.955Sb0.985 composition exhibited optimal performance, achieving an average power factor (PF) of 12.8 mu W K-2 cm-1 in the 300-525 K range. By considerably reducing the thermal budget and processing time, this approach significantly improves the energy payback time (EPBT) and reduces the carbon footprint of production, addressing the critical sustainability-performance trade-off that limits large-scale deployment. This result validates the capacity of the proposed fast synthesis route to yield performant MgAgSb-based samples and suggests that the optimal nominal composition is dependent on the specific production technique employed. Fundamentally, this work demonstrates the rapid and successful preparation of the desired alpha-MgAgSb phase using an easily scalable technique that does not require a perpetually inert atmosphere. This process utilises bulky precursor elements directly, significantly reducing production complexity, associated costs, and health hazards. This advancement provides a simpler and more industrially viable pathway for the transition of MgAgSb materials toward commercial availability.
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Entidade financiadora
Fundação para a Ciência e a Tecnologia
Programa de financiamento
6817 - DCRRNI ID
Número da atribuição
UID/Multi/04349/2019