Structure of Commensurate and Incommensurate Ordered Phases in the System ZrTiO ₄ –Zr ₅ Ti ₇ O ₂₄

The low‐temperature, Zr–Ti‐ordered, form of zirconium titanate has been investigated using high‐resolution transmission electron microscopy in order to characterize the incommensurate structure of phases with compositions ZrTiO 4 to near Zr 5 Ti 7 O 24 . Electron diffraction reveals that compositions with Zr : Ti between 5 : 7 and 1 : 1 have incommensurate superstructures, and phases close to 1 : 1 are commensurate with an a ‐axis repeat 2X that of the disordered structure. High‐resolution images show that the a ‐doubling in ZrTiO 4 corresponds to a new structure, one that consists of two Zr‐rich, distorted octahedral layers alternated with two Ti‐rich octahedral layers. The incommensurate compositions are composed of blocks of the 1 : 1 structure intercalated with blocks of the commensurate 5 : 7 structure, the latter having a tripled a ‐repeat and a ZTTZTT sequence of cation layers. The intercalation can be described as an “interface‐modulated” structure resulting from the quasiperiodic insertion of (100) faults with displacement vector R =–1/3 a ord in the ordered 5 : 7 phase. Although their spacing is variable, the faults are uniformly distributed in such a way as to produce incommensurate satellite reflections. The findings regarding the structure of ordered compositions in the ZrTiO 4 –Zr 5 Ti 7 O 24 system provide an improved framework for understanding the effects of ordering on the properties of zirconium titanate dielectric ceramics.