Local orderings in long-range-disordered bismuth-layered intergrowth structure

•The characteristic of the long-range-disordered (Bi3TiNbO9)2(Bi4Ti3O12) (223) structure was statistically analyzed, and the ordered -223- structure was speculated to be the thermodynamic stable state of the system.•The crystals of the -223- structure were successfully prepared for the first time by self-melt method.•The lower limit of the repeating units (L) to uniquely determine an independent intergrowth structure was speculated to be L=4.•The analysis inferred that the kinetic process is the controlling factor to limit the structural continuity and induce the long-range-disordered intergrowth structure.

A series of intergrowth bismuth-layered (Bi3TiNbO9)2(Bi4Ti3O12) (223) ceramics were prepared by conventional solid-state reaction to study the characteristics of the local orderings in long-range-disordered intergrowth structures. High-resolution high-angle annular dark-field (HAADF) imaging reveals the intergrowth structure composed of mixtures of -23-, -223-, -2223- and -22- sequences, while the -223- structure is the thermodynamic stable state of this intergrowth system. It was confirmed by the crystals of recurrent -223- structure prepared by self-flux method and the nature of the local ordering was discussed from their differences in repeating units. The statistics show that when repeating units reach 4 or higher, the independent -223- intergrowth ordering emerges clearly among the competing associated orderings. We infer it is the kinetic factor that induces local compositional variance to result in long-range disordered intergrowth structures.

Graphical abstractThe long-range-disordered intergrowth structure in a (Bi3TiNbO9)2(Bi4Ti3O12) (223) grain, which is composed of various types of local orderings, such as -22-, -23- and -223-.Figure optionsDownload full-size imageDownload as PowerPoint slide