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Crystallographic defects play a crucial role in cement hydration, with initial dissolution being dominated by the formation of etch pits that rely on the intersection of defects on surfaces. However, the defects present in cement particles have remained a mystery due to the lack of detailed direct observation at the atomic scale. In this study, we used scanning transmission electron microscopy to unravel the defects in alite particles at the single-atom level. Our observations identified different types of defects, including vacancies, doping, dislocations, rough surfaces, and grain boundaries. Atomic ordering in the alite crystal was further examined based on our single-atom recognition method. Our findings indicate that defects in cement particles may serve as reactive sites during the early hydration stage, facilitating the initial dissolution and providing nucleation sites for hydration products. This work provides insights into cement defect formation at the single-atom level and offers new opportunities in tuning the hydration process through defect engineering of cement particles. [ABSTRACT FROM AUTHOR]

Large superelastic deformation in ferroelastic-ferroelectrics (FMs) is a complex phenomenon involving multiple mechanisms operating simultaneously. Understanding how these mechanisms contribute corporately is critical to apply this useful property to the intrinsically brittle FMs, which can therefore display both excellent functional and mechanical performance. Here, we have directly observed and quantitatively analyzed in situ in a transmission electron microscope the three main mechanisms of twinning domain, phase transformation and mobile point defect contributing to extremely large superelastic deformation in single-crystal BaTiO 3 (5.0% strain) and Pb(Mg 1/3 Nb 2/3)O 3 -PbTiO 3 (10.1% strain). Our results reveal the hierarchical origin of large recoverable strain in "brittle" FMs. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Abstract LiNi 0.6 Mn 0.2 Co 0.2 O 2 is a promising cathode material with a high capacity for Li-ion batteries. However, the rapid capacity degradation in the high-voltage cycles constrain their further applications. Accordingly, the performances of LiNi 0.6 Mn 0.2 Co 0.2 O 2 have been systematically investigated using various microstructural characterizations as well as electrochemical analyses to explore its degradation mechanism. Our results indicate that the capacity decay of LiNi 0.6 Mn 0.2 Co 0.2 O 2 strongly depends on the charge cut-off voltage. For the cell that is cycled at 4.2 or 4.5 V, the degradation mechanism is primarily due to transformation from layered to rock salt structure on the particle surface, increasing the charge transfer impedance. For the cell that is cycled at 4.8 V, another two reasons should be considered. The irreversible structural change in the bulk lattice of LiNi 0.6 Mn 0.2 Co 0.2 O 2 during the high-degree delithiation process eventually disintegrates the secondary particles, resulting in the poor electrical contact between particles. Another one is that the insulating surface film which is generated on the surface of particles after cycling at 4.8 V increases the interfacial impedance of LiNi 0.6 Mn 0.2 Co 0.2 O 2. All these factors contribute to the overall capacity degradation at high voltages. Highlights • The capacity degradation of NMC 622 depends on the charge cut-off voltage. • Surface structural transition leads to degradation at 4.5 V or below. • Particle cracking accompanied with phase changes causes degradation at 4.8 V. • An insulating surface film also contributes to the capacity degradation at 4.8 V. [ABSTRACT FROM AUTHOR]