A deep lower-mantle (DLM) water reservoir depends on availability of hydrous minerals which can store and transport water into the DLM without dehydration. Recent discoveries found hydrous phases AlOOH (Z = 2) with a CaCl₂-type structure and FeOOH (Z = 4) with a cubic pyrite-type structure stable under the high-pressure–temperature (P-T) conditions of the DLM. Our experiments at 107–136 GPa and 2,400 K have further demonstrated that (Fe,Al)OOH is stabilized in a hexagonal lattice. By combining powder X-ray-diffraction techniques with multigrain indexation, we are able to determine this hexagonal hydrous phase with a = 10.5803(6) Å and c = 2.5897(3) Å at 110 GPa. Hexagonal (Fe,Al)OOH can transform to the cubic pyrite structure at low T with the same density. The hexagonal phase can be formed when δ-AlOOH incorporates FeOOH produced by reaction between water and Fe, which may store a substantial quantity of water in the DLM.

下地幔深水库（DLM）取决于含水矿物的可用性，这些含水矿物可以将水存储和输送到DLM中而不会脱水。最近的发现发现，在DLM的高压-高温（PT）条件下，具有CaCl ₂型结构的水相AlOOH（Z = 2）和具有立方黄铁矿型结构的FeOOH（Z = 4）是稳定的。我们在107–136 GPa和2,400 K下的实验进一步证明（Fe，Al）OOH稳定在六边形晶格中。通过将粉末X射线衍射技术与多颗粒索引相结合，我们能够确定a = 10.5803（6）Å和c的六角形水相。= 110 GPa时为2.5897（3）Å。六方（Fe，Al）OOH可以在低T下以相同的密度转变为立方黄铁矿结构。当δ-AlOOH掺入由水和Fe之间的反应产生的FeOOH时，可以形成六方相，这可能会在DLM中存储大量的水。