[Ca₂₄Al₂₈O₆₄]⁴⁺(4e^–) eletride, as the first room-temperature stable inorganic electride, has attracted intensive attention because of its fascinating chemical, electrical, optical, and magnetic properties. However, it usually needs synthesizing through a complicated multistep process involving high temperature (e.g., 1350 °C), severe reduction (e.g., 700–1300 ℃ for up to 240 h in Ca or Ti metal vapor atmosphere) and post-purification. Owing to the H₂O sensitivity of mayenite, the post-purification is quite troublesome once impurities are introduced. High-density, loosely bound encaged electrons with a low work function make it promise to possess practical applications. Therefore the facile method of massively producing the high-quality C12A7:e^– with high Ne is extremely desired. In this work, C12A7:e^– bulks are for the first time synthesized by simple spark plasma sintering process directly from a mixture of C12A7, CA and Ca powders under milder conditions (e.g., sintered at 1070 ℃ for 10 min in a vacuum). The obtained electride, which exhibits a relative density of 99%, an electron concentration of ~2.3×10²¹ cm^–3 and an obvious absorption peak at 2.5 eV, is obtained via SPS process at 1100 ℃ for 10 min. Electronic structure is also investigated by electron paramagnetic resonance. The occurrence of Dysonian characteristic, a typical feature of good electronic conductors, strongly suggests that the electrons are trapped in mayenite cavities. Furthermore, the obtained C12A7:e^– exhibits good sinterabilty on a crystal scale of 5–40 μm. Thermionic emission test results show that the thermionic emission begins to occur at 700 K and a large current density of 1.75 A/cm² is obtained in the electron thermal emission from a flat surface of the polycrystalline C12A7:e^– with an effective work function of 2.09 eV for a temperature of 1373 K with an applied electric field of ~35000 V/cm in a vacuum. Owing to no external reductant is needed, this developed route exhibits notable superiority over the conventional reduction method for phase-pure C12A7:e^–. Therefore, these results not only suggest a novel precursor for fabricating mayenite electride but also make it possible to produce efficiently the electride in large volume.

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In this paper, the evolution of the cavitation bubbles is researched. A model is developed to describe the cyclic chain-like cavitation cloud and analyze its structure stability in a thin liquid layer. By considering the effect of secondary acoustic radiation of bubbles, the dynamic equations of the bubbles in three zones of the cyclic chain are obtained. The secondary Bjerknes force is selected to explore the interaction between the bubbles in different regions. Numerical results showed that the newborn bubbles inside the pure liquid zone of the thin layer could be attracted by the bubbles at the cyclic chain-like bubble chain. The bubble number density could affect the coupling strength between bubbles, and it is closely related to the driving pressure. Therefore, the structure stability of cyclic chain-like cavitation cloud could be disrupted by the perturbations of the acoustic pressure. To verify our analysis, we observed the structure of cavitation cloud in a thin liquid layer in a strong acoustic field by using high speed camera. It is observed that the simultaneous collapse of local bubbles occurs, and pure liquid-like thin layers are distributed in the bubble cloud randomly. The boundary of the pure liquid-like thin layers is oscillated with the acoustic field, and the life of these liquid zones is about 4 acoustic cycles. The experiments results agree well with theoretical ones.