Fig. 8. XPS and time-of-flight secondary ion mass spectrometry measurements.

XPS spectra at the O 1s edge of Ni-substituted BaTiO₃ ceramics (A) at the as-sintered state and (B) after 4 weeks in ambient air. The red, blue, and black solid lines in (A) and (B) represented the fitted curves of the oxygen in a lattice, the oxygen vacancy, and the chemisorbed oxygen on the surface of the ceramics. The volume fraction of the chemisorbed oxygen peak substantially increased after air exposure. Time-of-flight secondary ion mass spectrometry (TOF-SIMS) 3D rendering maps of H⁺ signals in the (C) pure and (D) Ni-substituted BaTiO₃ ceramics that were treated by air exposure for 6 weeks (scale, 100 μm by 100 μm; sputter time, 0 to 3700 s).