Formation of new alumina by shearing at high pressure

The structures of inorganic solids sheared at high pressure more frequently persist at ambient conditions than those hydrostatically pressurized to high pressure. Accordingly, we can expect to fabricate materials with high-pressure structure to use them for practical purposes at ambient conditions. I, therefore, sheared α-alumina, at gradually heightened pressure up to 18 GPa at room temperature and took transmission X-ray diffraction patterns from the central area of the specimens on imaging plates, one year after the shearing. They showed broad diffused rings. This indicates that the sheared structure is highly disordered. The rings roughly correspond to a highly disordered structure consisting of simple cubic lattices, with the exception of two rings. Alumina with the former structure has not yet been reported. The latter rings correspond to those of alumina above 90 GPa (the structure is unknown). The fact mentioned above suggests the existence of an intermediate state between α-alumina and the alumina above 90 GPa. The above facts also suggest that the transformation mentioned above and the disordering of lattices contributed to plastic deformation of the specimen during the shearing.