Abstract A powder of transition alumina nanoparticles (including γ and a so-called δ-type) is compacted at room temperature in a diamond anvil cell (DAC) under pressures ranging from 5 GPa to 20 GPa. Characterization carried out on thin foils prepared by focused ion beam (FIB), from the compacted powder, unambiguously reveals plasticity. High resolution transmission electron microscopy (HRTEM) and electron diffraction also evidence phase transformation of nanoparticles under high pressure and nanoparticles show faceting parallel to the loading direction with a preferential crystallographic orientation of the facets corresponding to {220} planes of γ−Al2O3. It can also be deduced, from the comparison between the DAC experiments and in situ TEM nano-compression tests on single particles performed in a preceding work, that plasticity is driven by slip bands corresponding to {111} slip planes, common for a spinel structure, such as, for instance, γ−Al2O3. We also demonstrate that at ambient temperature the transition alumina phase is also prone to structural change under high pressures with the following sequence γ-Al2O3 → δ* Al2O3, these two phases coexisting, sometimes, in the same nanoparticle after compaction. Plasticity at room temperature in alumina nanoparticles and the subsequent phase transformation under pressure may have strong impacts on the process of alumina nanostructured ceramics.

中文翻译：

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纳米级过渡氧化铝纳米粒子在压力下的室温塑性和相变

摘要 过渡氧化铝纳米颗粒（包括 γ 和所谓的 δ 型）粉末在室温下在金刚石砧座 (DAC) 中在 5 GPa 至 20 GPa 的压力下压实。通过聚焦离子束 (FIB) 从压实粉末制备的薄箔上进行表征，明确地揭示了可塑性。高分辨率透射电子显微镜 (HRTEM) 和电子衍射也证明了纳米粒子在高压下的相变，纳米粒子显示出平行于加载方向的刻面，其中刻面的优先晶体取向对应于 γ-Al2O3 的 {220} 平面。从 DAC 实验与先前工作中对单个粒子进行的原位 TEM 纳米压缩测试之间的比较，也可以推断出，塑性由对应于 {111} 滑移面的滑移带驱动，常见于尖晶石结构，例如，γ-Al2O3。我们还证明，在环境温度下，过渡氧化铝相在高压下也容易发生结构变化，顺序为 γ-Al2O3 → δ* Al2O3，这两个相有时在压实后共存于同一个纳米颗粒中。氧化铝纳米颗粒在室温下的可塑性和随后在压力下的相变可能对氧化铝纳米结构陶瓷的工艺产生强烈影响。我们还证明，在环境温度下，过渡氧化铝相在高压下也容易发生结构变化，顺序为 γ-Al2O3 → δ* Al2O3，这两个相有时在压实后共存于同一个纳米颗粒中。氧化铝纳米颗粒在室温下的可塑性和随后在压力下的相变可能对氧化铝纳米结构陶瓷的工艺产生强烈影响。我们还证明，在环境温度下，过渡氧化铝相在高压下也容易发生结构变化，顺序为 γ-Al2O3 → δ* Al2O3，这两个相在压缩后有时共存于同一个纳米颗粒中。氧化铝纳米颗粒在室温下的可塑性和随后在压力下的相变可能对氧化铝纳米结构陶瓷的工艺产生强烈影响。