Direct Observation of Oxygen Atoms Taking Tetrahedral Interstitial Sites in Medium‐Entropy Body‐Centered‐Cubic Solutions

Abstract

Interstitial solutes, such as carbon in steels, are effective solid‐solution hardening agents. These alloying elements are believed to occupy the octahedral interstices in body‐centered‐cubic (bcc) metals. Using deep‐sub‐angstrom‐resolution electron ptychography, here the first experimental evidence to directly observe individual oxygen atoms in a highly concentrated bcc solid solution—the (TiNbZr)86O12C1N1 medium‐entropy alloy (MEA)—is provided, whereby the interstitial sites in which the oxygen atoms are located are discerned. In addition to oxygen interstitials residing in octahedral sites, the first unambiguous evidence of a switch in preference to the unusual tetrahedral sites at high oxygen concentrations is shown. This shift away from octahedral occupancy is explained as resulting from the extra cost of strain energy when the requisite displacement of the host atoms is deterred in the presence of nearby octahedral interstitials.

Probing Functional Structures, Defects, and Interfaces of 2D Transition Metal Dichalcogenides by Electron Microscopy

“…[ 106 ] Alternatively, the contrast contributions from the top and bottom sections (the two exposed cross‐sectional surfaces that might be damaged by the ion beam) can be entirely excluded through computational imaging methods. [ 107 ]…”

“…[106] Alternatively, the contrast contributions from the top and bottom sections (the two exposed crosssectional surfaces that might be damaged by the ion beam) can be entirely excluded through computational imaging methods. [107] One notable example utilizing cross-sectional STEM imaging is the identification of Janus MoSSe, a unique type of TMDs with a broken out-of-plane symmetry and vertical dipole (Figure 4a). [108] The design of this Janus TMDs starts from removing the upper layer of S atoms in CVD-grown monolayer MoS 2 via hydrogen plasma treatment, and then replacing the upper layer H atoms with Se atoms.…”

Over‐Stoichiometric Metastabilization of Cation‐Disordered Rock Salts

“…In recent years, outside of the field of battery materials research, it has been reported that over-stoichiometric cations may locate at interstitial sites in various types of fcc lattices, [37][38][39][40][41][42] hinting at the possibility of over-stoichiometric chemical spaces for rock salt structures. Moreover, a number of pioneering works have indicated that interstitial sites (e.g., tetrahedral sites) in the fcc-or near-fcc-type cathodes may be occupied by cations, which also suggests that rock salt structures may host extra cations.…”

Dynamic Homogenization of Internal Strain in Multi‐Principal Element Alloy via High‐Concentration Doping of Oxygen with Large Mobility

“…[27][28][29][30][31] The presence of residual strain, arising from modulus mismatch and atomic size differences, comprises both volumetric and shear components, resulting in significant spreading. [32][33][34] The inherent lattice distortion in MPEAs allows for the accommodation of more interstitial atoms, [35,36] further intensifying the lattice distortion. By capitalizing on the synergistic effects of inherent substitutional solid solution strengthening and extreme interstitial solid solution strengthening, the material strength may be optimized.…”