The detailed study of phase transition processes among various calcium sulfates is still insufficient in spite of its importance in artificial and natural processes. Here, the phase transformation γ-CaSO4 → β-CaSO4 → CaO is induced by electron beam irradiation and directly observed inside the transmission electron microscope (TEM). Relying on the real-time atomic-scale observation, the topological transition from γ-CaSO4 (hexagonal) to β-CaSO4 (orthorhombic) is investigated in detail, and the orientation relationship is determined: [0001]H//[001]O and (101̅0)H//(010)O. Furthermore, three β-CaSO4 variants related by 120° rotation are observed, which is theorized to occur during the transformation from hexagonal to orthorhombic structure. The possible transition mechanism is thus discussed. This work offers detailed information on the transition mechanism concerning the calcium sulfates, which might facilitate their industrial applications and possibly further understanding of rock deformation in the earth crust.

Knowledge regarding the phase and valence state evolution of molybdenum (Mo) and its oxides during the redox reaction is essential for advancing their energy applications (e.g., electrocatalysis), which unfortunately remains largely unexplored. Herein, the effects of atomic and electronic structures on the electrocatalytic performance of Mo/oxides core−shell structures are investigated on the basis of the combination of ex situ and in situ experiments. First, a two-step reaction pathway is revealed during the oxidation of nanoscale Mo: the formation of amorphous MoO 3 (A-MoO 3 ) shells followed by the nucleation of crystalline α-MoO 3 . It is shown that the electrocatalytic performance of A-MoO 3 is superior to that of α-MoO 3 , mainly due to more catalytically active sites in the former material. Furthermore, in situ transmission electron microscopy observations show that the A-MoO 3 shell can be rapidly reduced into metallic MoO 2 under reductive environment, which is likely to occur during the hydrogen evolution reaction measurement. Our in-depth characterization may contribute to the thorough and comprehensive understanding of the structural transition in Mo and its oxides during oxidative and reductive environments and thus serves as a reference for understanding the structure−property interplay for real energy applications.

One‐dimensional (1D) core‐shell heterostructures can exhibit novel and flexible properties when two different materials are combined. In this work, Pt nanoparticles are directly deposited onto CuO nanowires (NWs), forming 1D CuO−Pt core‐shell heterostructures with elastic and plastic behaviors dominating in the CuO‐core and Pt‐shell, respectively, under bending deformation. Interestingly, the plastically deformed Pt‐shell leads to a delayed or even terminated elasticity restoration of the CuO‐core NWs after unloading. Moreover, the release of the elasticity in CuO NW can be easily regulated not only via controlling the diameter of the CuO−Pt NWs, but also by thermal heating. The result shows a flexible 1D nanostructure with potential applications in micro/nano electro‐mechanical systems, such as mechanical energy storage and thermal sensors.

Two types of Mg–Al–O structures were successfully synthesized under high temperature (above 1173 K). Transmission electron microscopy and group theory analysis reveal the existence of cubic MgAl2O4 and an unreported monoclinic MgAlxOy phase with four domain variants. The structural relationship between these two phases is discussed in detail. The results shed light on the structural investigation of Mg–Al–O oxides, which are important mineral components of the Earth's lower mantle as well as substrates for the epitaxial growth of semiconductor films. Monoclinic MgAlxOy nanowires with domain boundaries may also provide a possible high‐strength candidate for industrial applications.

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