This paper aims to improve the density and thermal shock resistance of Y 2 O 3 ceramics for the preparation of ultra-pure high-temperature alloy crucible materials. The doping effect of MgF 2 content on the densification behavior, physical properties, and thermal shock resistance of Y 2 O 3 ceramics was systematically investigated in this paper. The results suggested that the presence of MgF 2 greatly promoted the growth of Y 2 O 3 grains and the transformation of the pore structure by liquid-phase sintering. And the mechanical properties of the MgF 2 -doped Y 2 O 3 ceramics were significantly improved. Besides, the marked improvement in the thermal shock resistance of MgF 2 -doped Y 2 O 3 ceramics was attributed to the synergistic action resulting from the growth of grain size and the enhancement of the crack deflection effect. In particular, the relative density of Y 2 O 3 ceramics doped with 1.5 wt% MgF 2 reached 96.4% and the residual flexural strength ratio after thermal shock achieved 45.0%, showing an excellent application prospect.
P2-NaxMnO2 has garnered significant attention due to its favorable Na+ conductivity and structural stability for large-scale energy storage fields. However, achieving a balance between high energy density and extended cycling stability remains a challenge due to the Jahn–Teller distortion of Mn3+ and anionic activity above 4.1 V. Herein, we propose a one-step in situ MgF2 strategy to synthesize a P2-Na0.76Ni0.225Mg0.025Mn0.75O1.95F0.05 cathode with improved Na-storage performance and decent water/air stability. By partially substituting cost-effective Mg for Ni and incorporating extra F for O, the optimized material demonstrates both enhanced capacity and structure stability via promoting Ni2+/Ni4+ and oxygen redox activity. It delivers a high capacity of 132.9 mA h g–1 with an elevated working potential of ≈3.48 V and maintains ≈83.0% capacity retention after 150 cycles at 100 mA g–1 within 2–4.3 V, compared to the 114.9 mA h g–1 capacity and 3.32 V discharging potential of the undoped Na0.76Ni0.25Mn0.75O2. While increasing the charging voltage to 4.5 V, 133.1 mA h g–1 capacity and 3.55 V discharging potential (vs Na/Na+) were achieved with 72.8% capacity retention after 100 cycles, far beyond that of the pristine sample (123.7 mA h g–1, 3.45 V, and 43.8%@100 cycles). Moreover, exceptional low-temperature cycling stability is achieved, with 95.0% after 150 cycles. Finally, the Na-storage mechanism of samples employing various doping strategies was investigated using in situ EIS, in situ XRD, and ex situ XPS techniques.
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