Epitaxial growth and dielectric properties of homologous $Srm−3Bi4TimO3m+3$ $(m=3,4,5,6)$ thin films

The first four members of Bi-layered $Srm−3Bi4TimO3m+3$ homologous series with $m=3,$ 4, 5, and 6, i.e., $Bi4Ti3O12,$ $SrBi4Ti4O15,$ $Sr2Bi4Ti5O18,$ and $Sr3Bi4Ti6O21,$ were grown on $SrTiO3$ (001) single-crystal substrates by pulsed-laser deposition. X-ray diffraction and high-resolution transmission electron microscopy (HRTEM) reveal that the films grew epitaxially with in-plane epitaxial alignment of $[11̄0]Srm−3Bi4TimO3m+3‖[010]SrTiO3.$ HRTEM cross-sectional images show that the films with $m=3,$ 4, and 5 are nearly free of intergrowth, whereas a number of growth defects were observed in the film with $m=6.$ Using an evanescent microwave probe, the room-temperature dielectric constants of these epitaxial films are measured to be $221±13,$ $205±15,$ $261±29,$ and $249±17$ for films with $m=3,$ 4, 5, and 6, respectively.