Why and how Ag is formed when electron beam irradiation takes place on a-Ag 2 WO 4 in a vacuum transmission electron microscopy chamber? To find an answer, the atomic-scale mechanisms underlying the formation and growth of Ag on a-Ag 2 WO 4 have been investigated by detailed in situ transmission electron microscopy (TEM) and field emission scanning electron microscopy (FE-SEM) studies, density (100) surface, are the most energetically favorable to undergo the diffusion process to form metallic Ag.Ab initio molecular dynamics simulations and the nudged elastic band (NEB) method were used to investigate the minimum energy pathways of these Ag atoms from positions in the first slab layer to outward sites on the (100) surface of a-Ag 2 WO 4 . The results point out that the injection of electrons decreases the activation barrier for this diffusion step and this unusual behavior results from the presence of a lower energy barrier process.

In this work, we investigated the effects of chemical substitution on the structural, electronic, and optical properties of α-Ag2-2xNixWO4 (0 ≤ x ≤ 0.08) solid solutions prepared by a facile microwave-assisted hydrothermal method. The results showed that the increase of Ni concentration in α-Ag2WO4 microcrystals as a host matrix caused a morphological transformation and a shift of the electronic and optical properties. Based on first principles calculations and using Wulff's construction, particle shapes and their transformations in α-Ag2WO4 and α-Ag2-2xNixWO4 can be affected by controlling the ratios of surface energy values between the different facets. In addition, theoretical calculations revealed that Ni substitution in α-Ag2WO4 is more favorable in the Ag2 and Ag4 positions, in which the local coordination of Ag atoms corresponds to clusters with coordination numbers of seven and four, respectively. This behavior could be related to the degree of medium-range structural disorder in α-Ag2-2xNixWO4 crystals. The experimental results were correlated with theoretical simulations to achieve a deeper understanding of the relationship between morphology and properties. These results provide the basis for a rational design for the compositional modulation of structural and optical properties.

In this paper, we investigate the structural and morphological changes caused by the electron-beam irradiation that led to the growth of complex extruded filaments on the surfaces of α-Ag2WO4. To provide a complete description of this phenomenon, both scanning electron microscope (SEM) and transmission electron microscope (TEM) were employed in this study. Our experimental results evidenced that the extruded material was able to exhibit growth on different crystallographic faces, depending on the kind of microscope adopted during the electron-beam irradiation. For a more complete analysis, different electron-beam current densities in TEM were used to investigate all in situ modifications in the microcrystals. For the first time, besides the metallic silver, the presence of silver oxides (Ag2O and Ag3O4) were detected in the composition of extruded material. The diffusion mechanisms related to morphological modifications in the samples irradiated in SEM and TEM were discussed in detail. The coprecipitation reaction in dimethyl sulfoxide was chosen as the synthetic route, which favored the appearance of rectangular rod-like α-Ag2WO4 microcrystals. A growth mechanism was proposed to explain the formation and growth processes of these microcrystals.

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