Complexions and stoichiometry of the 60.8°//[100](011) symmetrical tilt grain boundary in Mg2SiO4 forsterite: A combined empirical potential and first-principles study

Abstract

In this work we explore the low-energy complexions of the symmetrical tilt grain boundary (GB) 60.8°//[100](011) in forsterite through molecular dynamics and first principles calculations. Using a conservative sampling, we find six stoichiometric complexions with energies ranging from 0.66 to 1.25 J/m2. We investigate the segregation of MgO vacancy pairs, and find that in most cases it is more favorable for the vacancies to lie within the GBs than in the surrounding crystals, leading to new atomic structures. From these results we infer that at finite temperature when vacancies are present in the system, GBs are likely to absorb them and to be non-stoichiometric. We find many GB complexions containing a free oxygen ion, which may have profound implications for geological processes.

The Role of Grain Boundaries in Low‐Temperature Plasticity of Olivine Revealed by Nanoindentation

“…Similar subgrain boundaries to the SB sample have been described by Heinemann et al (2005) as arrays of edge dislocations with a periodic spacing of approximately 3 nm and a Burgers vector of [001] (see Figure 4, Heinemann et al, 2005). Further structural descriptions can be found in Adjaoud et al (2012) and Furstoss et al (2022). Schematic illustrations of the sample geometries are presented in Figure 1.…”

“…(2012) and Furstoss et al. (2022). Schematic illustrations of the sample geometries are presented in Figure 1.…”

“…We use pure forsterite bicrystal samples to investigate a subgrain boundary (SB, 13°, [100]/(016)) (e.g., Adjaoud et al., 2012; Gardés et al., 2021) and a high‐angle grain boundary (HAGB, 60°, [100]/(011)) (e.g., Figure 7 of Adjaoud et al., 2012; Furstoss et al., 2022). In our samples, the [100] axis represents the shared axis of rotation between the two crystals and (016) and (011) represent the plane parallel to the boundary plane in the subgrain‐boundary sample and in the high‐angle grain‐boundary sample, respectively.…”

Advancements and opportunities in piezo-(photo)catalytic synthesis of value-added chemicals

“…107 These crystals possess a centrally symmetric hexagonal lattice arranged in a triangular pattern, similar to monolayer crystals, are asymmetrically arranged, lack inversion centers, and exhibit asymmetric charge density distribution, thereby exhibiting piezoelectric effects. 108 Ma et al reported on the synthesis of molybdenum disulfide nanosheets via a hydrothermal method, which were then utilized in the piezocatalytic reduction process of carbon dioxide. 103 The experiment demonstrated that this material independently completes the entire carbon cycle chain from CO 2 capture to conversion, achieving an ultrahigh purity piezocatalytic CO production rate of 543.1 mmol g À1 h À1 .…”