Two new long-period structures related to β-alumina

Two new ordered forms of “β-alumina” with rhombohedral symmetry have been discovered and their structures deduced from one-dimensional electron microscope images of thick crystals. Referred to a hexagonal cell, their lattice parameters are a = 5.59Å, c = 169.5Å and a = 5.59Å, c = 339Å. A symbolism for describing structures related to that of β-alumina is proposed.