The High-Temperature and Intermediate Phases of Ferroelectric Aurivillius Compounds in Superspace. A Unified Approach

The recently proposed superspace description of the Aurivillius compounds in their ferroelectric phase is here extended to their high-temperature phases. The probable existence of an intermediate phase between the tetragonal high-symmetry and the ferroelectric phases is stressed. The relevant superspace groups,for both the tetragonal and the intermediate phases are identified. Consequently, the 3D space groups for the intermediate phases as a function of composition are predicted.