The high-pressure temperature phase diagram and transport properties of materials are of broad interest to planetary sciences and high-energy-density sciences and applications. Alumina (Al2⁢O3) or its various forms (e.g., solutions with other oxides or silicates) are important constituents in Earth's and super-Earths' mantles, common window materials in dynamic compression experiments, and standard pressure calibrators in diamond-anvil-cell experiments. Its structures and transport properties are of particular importance but have not been well studied at above 100 GPa pressures. Based on extensive first-principles molecular dynamics calculations, we obtain atomic level insights on structural differences and accurate results on electrical conductivity (𝜎dc), thermal conductivity (𝜅), and reflectivity of Al2⁢O3 in several phases at pressures of ∼130−1300GPa and temperatures of 4000–20 000 K. We find the solid-to-liquid state changes of Al2⁢O3 are accompanied by an insulator-to-semimetal transition with enhanced 𝜎dc and 𝜅, which is similar to other silicates and oxides and can facilitate magnetic field generation in deep interiors of rocky planets. We also find the solid-to-solid transition [from Rh2⁢O3⁡(II) to CaIrO3] is accompanied by negligible changes in 𝜎dc and 𝜅 at 160 GPa, contrary to previous expectations, whereas another higher pressure phase transition (CaIrO3 to U2⁢S3 at 450 GPa) is associated with increases in 𝜎dc and 𝜅. Furthermore, we show the transport properties can be enhanced by oxygen vacancy in Al2⁢O3, but are not significantly affected by forming solutions with MgSiO3, particularly when in the solid states.

中文翻译：

---

Al2O3 在极端条件下的熔融和传输特性


材料的高压温度相图和输运特性是行星科学和高能量密度科学及其应用的广泛兴趣。氧化铝 （Al2O3） 或其各种形式（例如，与其他氧化物或硅酸盐的溶液）是地球和超级地球地幔中的重要成分，是动态压缩实验中的常见窗口材料，也是金刚石-砧-电池实验中的标准压力校准器。它的结构和传输特性特别重要，但在 100 GPa 以上的压力下尚未得到很好的研究。基于广泛的第一性原理分子动力学计算，我们获得了原子级的结构差异见解，并在 ∼130-1300GPa 的压力和 4000-20 000 K 的温度下分几相获得了 Al2O3 的电导率 （σdc）、热导率 （κ） 和反射率的准确结果。我们发现 Al2O3 的固态到液态变化伴随着绝缘体到半金属的转变，σdc 和 κ 增强，这类似于其他硅酸盐和氧化物，可以促进岩石行星深处内部磁场的产生。 我们还发现，与 160 GPa 时 σdc 和 κ 的变化相反，[从 Rh2O3（II） 到 CaIrO3] 的固到固转变可以忽略不计，而另一个更高压力的相变（CaIrO3 在 450 GPa 下从 U2S3 到 U2S3）与 σdc 和 κ 的增加有关.此外，我们表明 Al2O3 中的氧空位可以增强传输性能，但与 MgSiO3 形成溶液不会显着影响，尤其是在固态时。