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The major hurdle of room temperature sodium-ion batteries (NIBs) for large-scale energy storage applications lies in developing new electrode materials with higher energy/power densities and improved durability. This work presents a novel Na-P3/Li 2 MnO 3 layered composite cathode with an alternating heteroepitaxial nanostructure fabricated by an in-situ composition modulation route. XRD structural refinement, synchrotron XAS and aberration-corrected HAADF-/ABF-STEM were employed to understand the structure evolution accompanying Li substitution. It is revealed that the in-situ formation of Li 2 MnO 3 (Li-O’3) changes the crystallographic and chemical features of the neighboring Na-P3 layered matrix significantly and leads to the alternating Na-P3/Li-O’3 heteroepitaxial nanostructure. This alternating heteroepitaxial nanostructure delivers an extremely high reversible capacity of ~ 210 mAh g −1 between 1.5 and 4.5 V vs. Na/Na + , much improved cycling stability and excellent electrode kinetics. Its enhanced electrochemical performance can be ascribed to the effective suppression of the P3-P3’’ phase transition and subsequent amorphization upon cycling to 4.5 V. [ABSTRACT FROM AUTHOR]

U 3 Si 2 nuclear fuel is corroded in deuterated steam with in situ neutron diffraction. Density functional theory is coupled with rigorous thermodynamic description of the hydride including gas/solid entropy contributions. H absorbs in the 2 b interstitial site of U 3 Si 2 H x and moves to 8 j for x ≥ 0.5. Hydriding forces lattice expansion and change in a/c ratio linked to site preference. Rietveld refinement tracks the corrosion reactions at 350–500 °C and preference for the 8 j site. Above 375 °C, formation of UO 2 , U 3 Si 5 and USi 3 take place in the grain boundaries and bulk. Hydriding occurs in bulk and precedes other reactions. [Display omitted] • In situ neutron diffraction measures U 3 Si 2 corrosion in deuterated steam. • Rigorous thermodynamic description of hydride using key entropy contributions. • H absorption at 2 b interstitial site of U 3 Si 2 H x , moves to 8 j site for x ≥ 0.5. • From 350 °C, U 3 Si 2 H x fragmented by 1–2% anisotropic lattice expansion. • From 375 °C, UO 2 , U 3 Si 5 and USi 3 form in bulk and in grain boundaries. [ABSTRACT FROM AUTHOR]