X-ray photoemission spectroscopy characterization of the electrode-ferroelectric interfaces inPt/Bi4

The interaction between Pt electrodes and ferroelectrics in ${\mathrm{P}\mathrm{t}/\mathrm{B}\mathrm{i}}_{4}{\mathrm{Ti}}_{3}{\mathrm{O}}_{12}(\mathrm{BTO})/\mathrm{Pt}$ and ${\mathrm{P}\mathrm{t}/\mathrm{B}\mathrm{i}}_{3.25}{\mathrm{La}}_{0.75}{\mathrm{Ti}}_{3}{\mathrm{O}}_{12}(\mathrm{BLT})/\mathrm{Pt}$ capacitors was investigated by ex situ x-ray photoelectron spectroscopy studies. The bare surface of crystals in BTO thin films consists of the regular Aurivillius structure, whereas that in BLT is composed of the intergrowth defects. At the annealed Pt-BTO and Pt-BLT interfaces,the Pt substitution at the BTO and BLT lattices results in Pt impurity defects, which can combine with oxygen vacancies ${(V}_{\mathrm{O}\ifmmode\ddot\else\textasciidieresis\fi{}})$ resulting in complex metal-impurity-oxygen-vacancy defect pairs. The complex defect pairs at the Pt-BTO interfaces are polar, nonswitchable, and able to pin polarizations of surrounding lattices inducing fatigue. In contrast, the intergrowth defects of BLT crystals behave as an intrinsic diffusion barrier to Pt, and therefore, the harmful defect pairs occurring at the Pt-BTO interfaces are practically absent for the Pt-BLT interfaces, which could be relevant to the reported different fatigue properties of BTO and BLT capacitors.