Fig. 2: The distribution of the doped element.

a Deconvolved XPS spectra of Nb 3d. b Fourier-transform curves of EXAFS data of W L3-edge (rW-O: The bond distance of W-O, CNW: The coordination number of W, R: R factor, σ2: Debye-Waller). c The ratio of W/(Ti+Nb) as a function of etching depth based on XPS of Bi3TiNbO9-W. d Atomic-level cross-section HAADF-STEM image of Bi3TiNbO9-W. e The corresponding EDS mapping images of elements (Bi, Ti, Nb, W).