[en] Li[Li_1/6Ni_1/4Mn_7/12]O_2−xF_x (x = 0, 0.025, 0.05, 0.075, 0.1) as the cathode materials for rechargeable lithium batteries have been synthesized via the co-precipitation method followed by a high-temperature solid-state reaction. Field emission scanning electron microscopy images exhibit that fluorine substitution catalyzes the growth of the primary particles. Although the initial discharge capacity decreases as the fluorine content increasing, the fluorine substituted materials present significant improvement in the cycling performance. Among the synthesized materials, Li[Li_1/6Ni_1/4Mn_7/12]O_1.95F_0.05 exhibits excellent high temperature (50 °C) cycling performance with a capacity retention of 93.7% after 30 cycles while the bare Li[Li_1/6Ni_1/4Mn_7/12]O₂ cathode exhibited only 73.7%

[en] The interdiffusion behavior of diffusion couples Ti-25Zr/Cu, Ti-50Zr/Cu and Ti-75Zr/Cu (at.%) at 973–1073 K was investigated by using electron probe microanalysis. The results show that the diffusion paths in all diffusion couples deviate away from the faster-diffusing Cu–Ti side. The diffusion paths pass the tie-line, across or parallel to, corresponding to the different diffusion layer structures and phase morphologies. The average effective interdiffusion coefficients and activation energies of Cu in both solid solutions and intermetallic compounds were determined. The diffusion coefficients of Cu in β(Ti, Zr) solid solution increase slightly and then decrease with the increase in Zr content, while the diffusion coefficients of Cu in Cu(Ti,Zr)${}_2$ intermetallic compound decrease with the increase in Zr content. The diffusion coefficients of Cu in Cu${}_{51}$Zr${}_{14}$ are the largest among all the intermetallic compounds in diffusion couples.

[en] Highlights: • 14H LPSO structure has been confirmed to be stable in the Mg–Cu–Y system. • Partial isothermal sections of the Mg–Cu–Y system from 300 to 450 °C have been established. • Reaction L + α-Mg ↔ 14H + Mg₂Cu has been determined in the Mg–Cu–Y system. • The thermal stability of the 14H phase in the Mg–Cu–Y system has been well studied. - Abstract: Phase equilibria in the Mg-rich Mg–Cu–Y system at 300, 400 and 450 °C have been experimentally investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), differential scanning calorimetry (DSC), electron probe micro-analyzer (EPMA) and transmission electron microscope (TEM). The results show that a long-period stacking ordered (LPSO) phase 14H is stable in the Mg–Cu–Y system, which is the only one ternary intermetallic compound that gets a thermodynamic equilibrium with the a-Mg phase. The equilibrium 14H phase has a very limited solid solution range, and can be nearly regarded as a ternary stoichiometric compound with a formulae as Mg₉₁Cu₄Y₅. The thermal stability of the 14H phase in the Mg–Cu–Y system has been well studied, which shows that the 14H phase disappears varying from 442 °C to 490 °C depending on the alloy composition. The isothermal sections of the Mg-rich Mg–Cu–Y system at 300, 400 and 450 °C have been finally established, and moreover, a quasi-peritectic reaction L + α-Mg ↔ 14H + Mg₂Cu has been determined occurring at 442 °C with an estimated liquid composition of Mg₇₇Cu₁₈Y₅

[en] Highlights: • Interdiffusion coefficients within Mg matrix solid solution. • Impurity diffusion coefficients of Y in Mg and Mg in Y. • Interdiffusion coefficients of intermetallic phases. • The vacancy diffusion mechanism plays the dominant role above 723 K. • The grain boundary diffusion mechanism plays the dominant role below 723 K. -- Abstract: The diffusion behavior in binary Mg-Y system was investigated using polycrystalline Mg/Y diffusion couples at temperatures ranging from 573 to 823 K. For all diffusion couples, electron microprobe analysis was utilized for the measurement of concentration profiles. The interdiffusion coefficients in Mg solid solution and intermetallic phases were determined via the Boltzmann-Matano and Heumann-Matano method, respectively. In addition, the Hall method was employed to extrapolate the impurity diffusion coefficients of Y in pure polycrystalline Mg and Mg in pure polycrystalline Y. The results showed that the interdiffusion coefficient in Mg solid solution increased with an increase of Y concentration, and the corresponding pre-exponential factor and activation energy both increased nearly linearly. The pre-exponential factor and activation energy for Y impurity diffusion in Mg were determined to be 2.36×10⁻⁸ (±9.0×10⁻⁹) m²/s and 85.61 (±2.0) kJ/mol, while those for Mg impurity diffusion in Y were determined to be 3.47×10⁻⁷ (±7.6×10⁻⁷) m²/s and 95.90 (±6.7) kJ/mol. Simultaneously, the pre-exponential factor and activation energy for interdiffusion in intermetallic phase Mg₂₄Y₅ were determined to be 9.96×10⁻⁹ (±2.9×10⁻⁹) m²/s and 68.98 (±2.0) kJ/molwhile those for Mg₂Y were determined to be 1.18×10⁻⁹ (±9.0×10⁻¹⁰) m²/s and 64.54 (±3.2) kJ/mol. Additionally, the vacancy diffusion was dominant mechanism above 723 K, while the grain boundary diffusion mechanism dominated below 723 K in polycrystalline Mg-Y binary system.

[en] Highlights: • A diffusional-displacive dominated formation mechanism for the β₁ phase has been uncovered. • A new displacive transformation mechanism of shear coupled with shuffle has been experimentally identified. • A new hcp/fcc transformation mechanism has been confirmed. The β₁ precipitate is a key strengthening-phase in Mg-rare-earth alloys, however, the formation mechanism concerning it has not yet been addressed. Herein, we have uncovered a diffusional-displacive dominated formation mechanism for the β₁ phase, using aberration-corrected scanning transmission electron microscopy observation combined with first-principles calculations, in an aged MgSm model alloy system. Shear of the nucleated {$10\overline{1}0$}_hcp zig-zag monolayers along a direction parallel to _fcc with a shear angle of ~5.26°, followed by atoms shuffling on the non-close-packed {$10\overline{1}0$}_hcp planes, can transform the hexagonal close-packed Mg₃Sm structure (β” or β_H’ intermediate phase) to the face-centered-cubic structure Mg₃Sm (β₁ phase). Besides, the formation of the β₁ phase can also be realized from the other β_S’ or β_L’ intermediate phase (c-bco, Mg₇Sm) via solute diffusion coupled with shuffle transformation manner. A new habit plane of {$10\overline{1}0$}_hcp // {$1\overline{1}0$}_fcc and [0001]_hcp // [110]_fcc on the non-closed packed plane has been identified, which is completely different from the traditional displacive transformation mechanism usually happened on the closed-packed plane. This finding enriches the diffusional-displacive transformations.