Structure of Commensurate and Incommensurate Ordered Phases in the System ZrTiO4–Zr5Ti7O24

Abstract

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 ZrTiO4 to near Zr5Ti7O24. 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 ZrTiO4 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 aord 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 ZrTiO4–Zr5Ti7O24 system provide an improved framework for understanding the effects of ordering on the properties of zirconium titanate dielectric ceramics.