372
T. A. Khalyavka et al.
Fig. 8 XPS a Ti 2p, b O 1s and c La 3d core-level spectra and d XPS valence band spectra
(including some higher core-level lines) of (1) 1La/TiO 2 and (2) 2La/TiO 2
Table 4 Binding energies
(eV) of TiO 2 , 1La/TiO 2, and
2La/TiO 2 (precision of
determination is ±0.1 eV)
Core-level
TiO 2
1La/TiO 2
2La/TiO 2
Ti 2p 3/2
458.6
458.9
458.1
Ti 2p 1/2
464.3
464.6
463.8
O 1s
530.0
530.5
529.9
La 3d 5/2
–
835.1
835.3
La 3d 3/2
–
851.9
852.1
sample the charge state of Ti atoms is intermediate between +4 and +2. Obviously,
titanium atoms can capture part of the electrons and reduce to Ti
3+ or Ti
2+ (Ti
4+
+
e
−
→ Ti
3+ ).
The XPS spectra of O 1 s relevant to O
2− ions in TiO 2 show an intense signal at
530.5 eV for 1La/TiO 2 and 529.9 eV for 2La/TiO 2 (Fig. 8b). This peak is attributed
to Ti-O and OH groups in TiO 2 and the shift of this core-level spectrum is 0.6 eV
[41]. The binding energy of the O 1s core-level spectrum decreases when going from
1La/TiO 2 to 2La/TiO 2 (Table 1), while the charge state of La does not change in this
sequence of compounds (Fig. 8c).
The charge state of La in the samples La/TiO 2 corresponds to +3 (La 2 O 3 ) (Table 4)
[39].