Nanoscale Structural Evolution and Anomalous Mechanical Response of Nanoglasses by Cryogenic Thermal Cycling

One of the central themes in the amorphous materials research is to understand the nanoscale structural responses to mechanical and thermal agitations, the decoding of which is expected to provide new insights into the complex amorphous structural-property relationship. For common metallic glasses, their inherent atomic structural inhomogeneities can be rejuvenated and amplified by cryogenic thermal cycling, thus can be decoded from their responses to mechanical and thermal agitations. Here, we reported an anomalous mechanical response of a new kind of metallic glass (nanoglass) with nanoscale interface structures to cryogenic thermal cycling. As compared to those metallic glasses by liquid quenching, the Sc₇₅Fe₂₅ (at. %) nanoglass exhibits a decrease in the Young’s modulus but a significant increase in the yield strength after cryogenic cycling treatments. The abnormal mechanical property change can be attributed to the complex atomic rearrangements at the short- and medium- range orders due to the intrinsic nonuniformity of the nanoglass architecture. The present work gives a new route for designing high-performance metallic glassy materials by manipulating their atomic structures and helps for understanding the complex atomic structure–property relationship in amorphous materials

X‑ray Absorption Spectroscopy and In-Operando Neutron Diffraction Studies on Local Structure Fading Induced Irreversibility in a 18 650 Cell with P2–Na₂/3Fe₁/3Mn₂/3O₂ Cathode in a Long Cycle Test

P2–Na_2/3[Fe_1/3Mn_2/3]­O₂ (NFMO) crystal with a maximum capacity of ∼150 mAh was synthesized by a solid-state annealing method and used as a cathode in a sodium ion battery. By combining focused-ion beam section scanning electron microscopy, ex-situ X-ray absorption spectroscopy, X-ray photoemission depth profiling, and in-operando neutron diffraction, we found that Na ion intercalation and extraction distort the local structure in NFMO crystal, resulting in irreversibility of the sodium ion battery (SIB). This reaction pathway is controlled by the transformation kinetics of the Fe sites from octahedral (O_h) to tetragonal (T_d) in the charge and discharge processes. For a SIB operated at 2.0 to 3.8 V, steady kinetics between the Na intercalation and chemical state evolution on the Fe sites enable the homogeneous restructuring in both local and global regimes in NFMO crystal. For a SIB operated at 2.0 to 4.5 V, substantially higher kinetics in the Fe chemical state evolution induce a dramatic lattice expansion. This expansion cracks the interface between the P2 and Na intercalated regions, thereby causing substantial irreversibility of NFMO in a SIB