Impact of Surface Roughness on Recrystallization of an α-Al2O3(001) Single Crystal to α-AlO(OH) Diaspore Microcrystals.

We demonstrate that the surface of an α-Al2O3(001) single crystal recrystallizes to α-AlO(OH) under ultrahigh pressure (8 GPa) at 600 °C. The recrystallization depends on the degree of surface roughness. A polished surface topotaxially recrystallizes to (100)-oriented α-AlO(OH) microcrystals, while unpolished surface recrystallizes to polycrystalline α-AlO(OH). This study demonstrates a new synthetic route to obtain oriented crystals of ultrahigh-pressure-phase materials and paves the way for the investigations of the physical and chemical properties of such materials.