TY - GEN A1 - Morales, Carlos A1 - Leinen, Dietmar A1 - Flores, Eduardo A1 - Muñoz-Cortes, Esmeralda A1 - Leardini, Fabrice A1 - Ares, José Ramón A1 - Flege, Jan Ingo A1 - Soriano, Leonardo A1 - Ferrer, Isabel J. A1 - Sanchez, Carlos T1 - Imaging the Kirkendall effect in pyrite (FeS2) thin films: Cross-sectional microstructure and chemical features T2 - Acta Materialia N2 - This investigation provides novel data on the structure and chemical composition of pyrite thin films and new hints concerning their formation mechanism. From TEM-HAADF data, it has been found that the films are composed of two different layers: one is very compact and the other one is quite porous with many voids separating a few groups of grains. This porous layer is always in direct contact with the substrate, and its thickness is quite similar to that of the original Fe film. The average size of pyrite grains is equal in both layers, what suggests that the same process is responsible for their formation. Concentration profiles of sulfur, iron and some impurities (mainly sodium and oxygen from the glass substrate) through both layers are given in this work, and thus chemical inhomogeneities of the films are proved by the obtained stoichiometric ratios (S/Fe). Moreover, Na from sodalime glass substrates mainly accumulates at the pyrite grain boundaries and barely dopes them. The obtained results support the hypothesis that the iron sulfuration process essentially induces the diffusion of iron atoms, what leads to the porous layer formation as a manifestation of the Kirkendall Effect. Therefore, it seems that the same mechanisms that operate in the synthesis of surface hollow structures at the nanoscale are also active in the formation of pyrite thin films ranging from several tens to hundreds of nanometers. KW - Pyrite KW - Transmission electron microscopy (TEM) KW - Cross-section KW - Kirkendall effect KW - Sodium doping Y1 - 2021 U6 - https://doi.org/10.1016/j.actamat.2020.116582 SN - 1359-6454 SN - 1873-2453 VL - 205 ER - TY - GEN A1 - Morales, Carlos A1 - Pascual, Antonio A1 - Leinen, Dietmar A1 - Flores, Eduardo A1 - Muñoz-Cortes, Esmeralda A1 - Leardini, Fabrice A1 - Ares, José Ramón A1 - Flege, Jan Ingo A1 - Soriano, Leonardo A1 - Ferrer, Isabel J. A1 - Sanchez, Carlos T1 - Reaction Mechanism and Kinetic Model of Fe Thin Film Transformation into Monosulfides (FeS): First Step of the Fe Films Sulfuration Process into Pyrite T2 - The Journal of Physical Chemistry C N2 - The sulfuration of metallic iron layers into pyrite (FeS2) is preceded by an initial stage characterized by the iron transformation into monosulfide, which acts as a precursor of the disulfide. This work presents a comprehensive reaction and kinetic model of the sulfuration reaction of metallic iron thin films into monosulfides when a molecular sulfur (S2) atmosphere is used. By slowing down the sulfuration reaction, we have been able to follow in situ the evolution of the transport properties (electrical resistivity and Seebeck coefficient) of the Fe films during their sulfuration reaction to monosulfides. We show that two different stages characterize this initial sulfuration: (1) the transformation of Fe into hexagonal pyrrhotite (Fe → Fe1–xSH) and (2) a partial crystallographic transformation of this hexagonal pyrrhotite into orthorhombic pyrrhotite (Fe1–xSH → Fe1–xSO). A two-step process can explain the pyrrhotite hexagonal phase formation, being first controlled by the surface adsorption of S2 on the external sample interface (S2/pyrrhotite) and second by the diffusion of Fe atoms through the formed pyrrhotite layer. By deducing the corresponding kinetic equations in terms of the experimental parameters (S2 partial pressure and thicknesses of the layers of present species), we can explain the evolution of the electrical resistance and Seebeck coefficient of the original Fe film during its transformation into monosulfide. At the same time, the appearance of the Kirkendall effect during the monosulfide phase formation is experimental and formally justified. The comprehensive description of this first stage of the complete sulfuration process of the Fe film into pyrite provides a layout to deeply discuss the influence of these intermedium phases on the final iron disulfide film characteristics and the appearance of potential film defects related to the experimental growth conditions. KW - Fe thin films KW - sulfuration KW - kinetics KW - transport properties KW - Kirkendall effect KW - Seebeck coefficient KW - resistivity Y1 - 2022 U6 - https://doi.org/10.1021/acs.jpcc.2c02060 SN - 1932-7455 SN - 1932-7447 VL - 126 IS - 32 SP - 13870 EP - 13883 ER -