Growth and local structure of BiFeO3 thin films with giant tetragonality on SrRuO3-buffered SrTiO3(001) substrate by ion beam sputtering

Abstract

Rhombohedral (R-) and tetragonal-like (T-) BiFeO3 (BFO) mixed-phase thin films and single R-phase BFO thin films have been grown on SrRuO3-buffered SrTiO3 (STO) (001) substrate by ion beam sputtering. From X-ray diffraction study, it was found that T-BFO and R-BFO mixed-phase thin films can be grown at a low oxygen partial pressure of 1 mPa, and the lattice parameters of the T-BFO and R-BFO were a = 0.381 nm, c = 0.461 nm (c/a = 1.22), and a = 0.394 nm and c = 0.400 nm (c/a = 1.02), respectively. High-resolution high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) observation and energy dispersive X-ray analysis (EDXA) mappings have revealed a clear T-BFO lattice and a–c domain in the middle of the thin films. However, Bi-rich and Fe-rich secondary phases were also found with the T-BFO phase. Therefore, it can be concluded that secondary phases such as Bi2O3 or Bi-poor phase are needed for T-BFO formation on STO (001) substrate, and the a–c domain formation does not occur by stress relaxation but matching of the growth directions of different domains.